Patent Description:
Secondary batteries represented by lithium ion secondary batteries are widely used in electric vehicles and consumer electronic products due to their advantages of high energy density, high output power, long cycle life and low environmental pollution. However, the secondary batteries, when undergoing abnormal conditions such as nail penetration, are liable to be short circuited. In the case of short circuit, a large current together with a large amount of short circuit heat would be generated in the battery, which is likely to cause smoking, igniting, or even exploding of batteries. This would lead to a big safety risk. In order to reduce the safety risk of batteries, it is necessary to improve the nail penetration safety performance of batteries.

<CIT> discloses a composite current collector comprising a polymer support layer having a thickness of <NUM> to <NUM> microns, wherein the polymer support film is selected from the group consisting of polystyrene, polyethylene terephthalate, polycarbonate, polypropylene and polyamide; conductive metal layers with a thickness of less than <NUM> microns; and protective metal layers with a thickness of <NUM>-<NUM>.

<CIT> discloses a composite current collector comprising a support layer composed of polyethylene terephthalate (PET) or polyimide (PI) with a thickness of <NUM>-<NUM> microns, coated on sides with a first protection layer of nickel or alumina having a thickness of <NUM>-<NUM> nanometers, and further coated with an aluminum layer of <NUM> to <NUM> microns, which is vapor-deposited.

A first aspect of the present invention provides a positive current collector as defined in the independent claims <NUM> or <NUM>.

A second aspect of the present invention provides a positive electrode plate including a positive current collector and a positive active material layer arranged on the positive current collector, wherein the positive current collector is the positive current collector according to the first aspect of the present invention.

A third aspect of the present invention provides a battery including a positive electrode plate, a negative electrode plate, a separator and an electrolyte, wherein the positive electrode plate is the positive electrode plate according to the second aspect of the present invention.

A forth aspect of the present invention provides an apparatus including the battery according the third aspect of the present invention.

The positive current collector provided in the present application includes a conductive layer having a smaller thickness which is arranged on at least one surface of the support layer, which is beneficial to increasing the weight energy density of the battery. Especially, when the battery undergoes abnormal conditions such as nail penetration, burrs generated on the conductive layer would be greatly reduced as compared with the existing metal current collector, thereby reducing the probability that the burrs on the conductive layer pierce separator to contact with the counter electrode. As a result, the risk of internal short circuit in the battery is significantly reduced. Moreover, in the positive current collector, the support layer has a resistivity greater than that of the conductive layer. Accordingly, the battery would have a larger short-circuit resistance when an internal short-circuit occurs. Hence, short-circuit current and thus short-circuit heat generation are reduced, and further, the nail penetration safety performance of the battery is improved. In addition, when the positive current collector has a tensile strain of <NUM>% or more, the conductive layer has a sheet resistance growth rate T ≥ <NUM>%. Therefore, when the battery undergoes abnormal conditions such as nail penetration, the short-circuit resistance of the positive current collector may be further increased, as a result, the safety performance of battery is improved by further increasing the short-circuit resistance, reducing short-circuit current and reducing heat generated from short-circuit and the like. In particular, local conductive network would be cut off when the nail penetration occurs, so as to inhibit short-circuit over large area or even the entire area of battery. Thus, the damage to battery would be limited to the site of nail penetration, forming "Point Break" only without affecting the normal operation of the battery within a certain period of time. Therefore, the battery adopting the positive current collector according to the present application has higher nail penetration safety performance.

When the positive current collector has a tensile strain of <NUM>%, the conductive layer has a sheet resistance growth rate T<NUM> ≤ <NUM>%. In this instance, the resistance resulted from tensile deformation of the conductive layer having a smaller thickness would be prevented from increasing sharply, so that the positive current collector could have good electrical conductivity and current collecting performance. Hence, the battery has low impedance and low polarization, so that the battery additionally has higher electrochemical performance.

The apparatus of the present application includes the battery provided in the present application, and thus has at least advantages identical to those of the battery.

In order to explain the technical solutions of the embodiments of the present application more clearly, the drawings for embodiments of the present application will be briefly described below. A person of ordinary skill in the art can obtain other drawings based on the drawings without a creative work.

In order to explain the object, technical solution, and technical effects of the present application apparent more clearly, hereinbelow the present application will be further described in detail with reference to the embodiments. It should be understood that the embodiments described in the present description are only for explaining the present application, and are not intended to limit the application.

For the sake of brevity, only certain numerical ranges are explicitly disclosed herein. However, any lower limit may be combined with any upper limit to form a range that is not explicitly described; and any lower limit may be combined with other lower limits to form range that is not explicitly described. Likewise, any upper limit may be combined with any other upper limit to form a range that is not explicitly described. Further, although not explicitly specified, each point or single value between the endpoints of the range is included in the range. Thus, each point or single value, as its own lower limit or upper limit, can be combined with any other point or single value or combined with other lower limit or upper limit to form a range that is not explicitly specified.

In the description herein, it should be noted that, unless otherwise stated, the recitation of numerical ranges by "no less than" and "no more than" include all numbers within that range including the endpoints. As used herein, the recitation of "more" in the phrase "one or more" means two or more.

The above-stated summary of the present application is not intended to describe each and every embodiment or implementation disclosed in this application. The following description illustrates exemplary embodiments more specifically. In many places throughout the application, guidance is provided by means of a series of embodiments, which can be applied in various combinations. In each instance, the enumeration is only a representative group and should not be interpreted as exhaustive.

The first aspect of the present application provides a positive current collector, which, compared with the existing positive current collector of metal aluminum foil, has improved nail penetration safety performance.

<FIG> schematically shows a positive current collector <NUM> as an example. As shown in <FIG>, the positive current collector <NUM> may include laminated support layer <NUM> and conductive layer <NUM>, wherein the support layer <NUM> has a first surface 101a and a second surface 101b opposite to each other in its thickness direction, and the conductive layer <NUM> is laminated on the first surface 101a and the second surface 101b of the support layer <NUM>.

<FIG> schematically shows a positive current collector <NUM> as another example. As shown in <FIG>, the positive current collector <NUM> may include laminated support layer <NUM> and conductive layer <NUM>, wherein the support layer <NUM> has a first surface 101a and a second surface 101b opposite to each other in its thickness direction, and the conductive layer <NUM> is laminated on the first surface 101a of the support layer <NUM>. Of course, the conductive layer <NUM> may also be laminated on the second surface 101b of the support layer <NUM>.

In the positive current collector <NUM> of the present application, the conductive layer <NUM> has a thickness D<NUM> satisfying <NUM> ≤ D<NUM> ≤ <NUM>, and when the positive current collector <NUM> has a tensile strain of ≥<NUM>%, the conductive layer <NUM> has a sheet resistance growth rate of T ≥ <NUM>%.

In the positive current collector <NUM> of the present application, a conductive layer <NUM> having a smaller thickness is arranged on at least one surface of the support layer <NUM>, which is conducive to improving the weight energy density. Particularly, when the battery undergoes abnormal conditions such as nail penetration, burrs generated on the conductive layer <NUM> would be greatly reduced as compared with the existing metal aluminum foil, thereby reducing the probability that the burrs on the conductive layer <NUM> pierce separator to contact with the counter electrode. As a result, the risk of internal short circuit in the battery is significantly reduced. Moreover, in the positive current collector <NUM>, the support layer <NUM> has a resistivity greater than that of the conductive layer <NUM>. Accordingly, the battery would have a larger short-circuit resistance when an internal short-circuit occurs. Hence, short-circuit current and thus short-circuit heat generation are reduced, and further, the nail penetration safety performance of the battery is improved. In addition, when the positive current collector <NUM> has a tensile strain of greater than or equal to <NUM>%, the conductive layer has a sheet resistance growth rate T<NUM> ≥ <NUM>%. Therefore, when the battery undergoes abnormal conditions such as nail penetration, the short-circuit resistance of the positive current collector may be further increased, as a result, the safety performance of battery is improved by further increasing the short-circuit resistance, reducing short-circuit current and reducing heat generated from short-circuit and the like. In particular, local conductive network would be cut off when the nail penetration occurs, so as to inhibit short-circuit over large area or even the entire area of battery. Thus, the damage to battery would be limited to the site of nail penetration, forming "Point Break" only without affecting the normal operation of the battery within a certain period of time.

Therefore, the batteries, adopting the positive current collector <NUM> according to the present application, have higher nail penetration performance.

In some embodiments, when the positive current collector <NUM> has a tensile strain ε of <NUM>%, the conductive layer <NUM> has a sheet resistance growth rate T<NUM> of ≤ <NUM>%. The positive current collector <NUM> is often subjected to stretching, for example in the case that the positive electrode plate <NUM> is rolled during the processing of the positive electrode plate <NUM> or expands during application in the battery, thereby resulting in a tensile strain. When the positive current collector <NUM> has a tensile strain of <NUM>%, the conductive layer <NUM> has a sheet resistance growth rate T<NUM> of ≤ <NUM>%. In this instance, the resistance resulted from tensile deformation of the conductive layer <NUM> having a smaller thickness would be effectively prevented from increasing sharply, so that the positive current collector <NUM> could maintain good electrical conductivity and current collecting performance during further processing and application in secondary batteries. By adopting the positive current collector <NUM>, the secondary batteries would have low impedance and low polarization, so that the secondary batteries have higher electrochemical performance together with for example higher rate performance and cycle performance.

Furthermore, when the positive current collector <NUM> has a tensile strain ε of <NUM>%, the conductive layer <NUM> has a sheet resistance growth rate T<NUM> of ≤ <NUM>%. Furthermore, when the positive current collector <NUM> has a tensile strain ε of <NUM>%, the conductive layer <NUM> has a sheet resistance growth rate T<NUM> of ≤ <NUM>%.

In embodiments herein, the tensile strain ε of the positive current collector <NUM> may be calculated according to formula ε=ΔL/L×<NUM>%, where ΔL is the elongation of the positive current collector <NUM> when being subjected to stretching, and L is the original length of the positive current collector <NUM>, i.e. the length of the positive current collector <NUM> before being subjected to stretching.

When the positive current collector <NUM> has a certain tensile strain ε, the sheet resistance growth rate T of the conductive layer <NUM> may be measured by a method well known in the art. As an example, the measurement comprise cutting the positive current collector <NUM> into a sample of <NUM>×<NUM>, measuring the sheet resistance of the central area of the sample by means of a four-probe method, recorded as R<NUM>; then subjecting the central area of the sample to stretching on a tensile tester, where an initial position is set, the center area of the sample with a length of <NUM> is clamped between clamps and is subjected to stretching at a speed of <NUM>/min, and then the stretching stops when the tensile distance is the product of L (<NUM>) and ε, that is, the tensile distance is ΔL; taking off the sample after stretching to measure the sheet resistance of the conductive layer <NUM> in the central area of the stretched sample, recorded as R<NUM>; and calculating the sheet resistance growth rate T of the conductive layer <NUM> when the positive current collector <NUM> has a tensile strain ε according to formula T=(R<NUM>-R<NUM>)/R<NUM>×<NUM>%. The tensile tester may be an Instron <NUM> tensile tester available from Instron, USA.

An exemplary method for measuring the sheet resistance of the sample by means of a four-probe method is as follows: using RTS-<NUM> double-electric four-probe tester, the test is conducted at a temperature of <NUM>±<NUM> under <NUM> MPa, with a relative humidity of ≤ <NUM>%. The test is performed by cleaning the surface of the sample, then placing it horizontally on the test bench; putting down the four probes so that the probes are in good contact with the surface of the sample; then calibrating the current range of the sample under automatic test mode, so as to measure the sheet resistance under a suitable current range; collecting <NUM> to <NUM> data points of the same sample for analyzing the accuracy and error of the measuring data; and taking the average value, which is recorded as the sheet resistance value of the sample.

In some embodiments, the support layer <NUM> has a thickness D<NUM> satisfying <NUM> ≤ D<NUM> ≤ <NUM>. For example, the support layer <NUM> may have a thickness D<NUM> of <NUM> or less, <NUM> or less, <NUM> or less, <NUM> or less, <NUM> or less, or <NUM> or less, and may have a thickness D<NUM> of <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more. Preferably, <NUM> ≤ D<NUM> ≤ <NUM>. Preferably, <NUM> ≤ D2 ≤ <NUM>. Preferably, <NUM> ≤ D<NUM> ≤ <NUM>.

Suitable thickness D<NUM> allows the support layer <NUM> have sufficient mechanical strength so that it is not likely to break during processing and application, and could well protect and support the conductive layer <NUM>, thereby ensuring good mechanical stability and operating stability of the positive current collector <NUM>, and further resulting in relatively long service life of the positive current collector <NUM>. The support layer <NUM> having the appropriate thickness is also advantageous to allowing the battery have smaller volume and weight, so as to increase the energy density of the battery.

In some preferred embodiments, the support layer <NUM> has a volume resistivity of greater than or equal to <NUM>×<NUM> -<NUM> Ω·m. Since the support layer <NUM> has a large volume resistivity, in the case of abnormal conditions such as nail penetration of the battery, the short-circuit resistance would increase when an internal short circuit occurs in the battery. Accordingly, the safety performance of the battery is improved. The support layer <NUM> is preferably a support layer having insulating properties.

In embodiments herein, the volume resistivity of the support layer <NUM> is the volume resistivity at a temperature of <NUM>, which can be measured by methods well known in the art. As an example, the measurement is conducted under conditions of constant temperature, normal pressure and low humidity (20C, <NUM>. 1MPa, RH≤<NUM>%), a sample of support layer <NUM> is prepared to be a round sheet having a diameter of <NUM> (the sample size could be adjusted according to the actual size of the test instrument), and the measurement is conducted by means of a three-electrode surface resistivity method according to GB T <NUM>-<NUM> on an insulation resistance tester with a precision of 10Ω. The measuring method is as follows: placing the sample of round sheet between two electrodes, and applying a potential difference between the two electrodes, wherein the current as generated will distribute in the sample of round sheet and is measured by a picoammeter or electrometer, so as to avoid the measurement error due to including the surface leakage current in the measurement process. The reading is the volume resistivity in Ω•m.

In some embodiments, the support layer <NUM> may have an elongation at break that is greater than or equal to that of the conductive layer <NUM>. In this way, when the secondary batter undergoes abnormal conditions such as nail penetration, the burrs on the support layer <NUM> can cover those on the conductive layer <NUM> and thus cover the surface of the nail so as to prevent the burrs of the conductive layer <NUM> from being in direct contact with the counter electrode. Thus, the internal short circuit in the battery is suppressed. In addition, since the support layer <NUM> has a large volume resistivity, when an internal short circuit occurs in the battery, the short-circuit resistance would be significantly increased, and thus short-circuit current and short-circuit heat generation are significantly reduced. Accordingly, the nail penetration safety performance of the battery is improved.

Preferably, the support layer <NUM> has an elongation at break that is higher than that of the conductive layer <NUM>. Since the conductive layer <NUM> has a relatively small ductility and the support layer <NUM> has a relatively large ductility, when the battery undergoes abnormal conditions such as nail penetration, the conductive layer <NUM> is stretched, and at the same time the support layer <NUM> covers the surface of the nail so that the nail is isolated from the conductive layer <NUM>. As a result, the local conductive network is cut-off well, thereby inhibiting short-circuit on a large area of the battery or even on the entire battery. As such, damages of the battery caused by nail penetration could be limited to the penetration site well, for example, resulting in "Point Break" only, without affecting the normal operation of the battery within a certain period of time.

Optionally, the support layer <NUM> has an elongation at break of greater than or equal to <NUM>%. Preferably, the support layer <NUM> has an elongation at break of greater than or equal to <NUM>%.

The elongation at break may be determined using methods well known in the art. As an example, the method comprises cutting the support layer <NUM> into a sample of <NUM>×<NUM>; conducting a tensile test on a tensile tester under normal temperature and pressure (<NUM>, <NUM>. 1MPa), where an initial position is set so that the sample length between the clamps is <NUM>, and the tensile speed is <NUM>/min; recording the displacement y (mm) of the instrument at the time of breaking due to stretching; and finally calculating the elongation at break according to (y/<NUM>)×<NUM>%. The tensile tester may be an Instron <NUM> tensile tester available from Instron, USA. The elongation at break of the conductive layer <NUM> may be measured in the same manner conveniently.

In some embodiments, the support layer <NUM> may have a Young's modulus E of ≥ <NUM> GPa. The support layer <NUM> has rigidity, and thus could support the conductive layer <NUM>, thereby ensuring the overall strength of the positive current collector <NUM>. During the processing of the positive current collector <NUM>, the support layer <NUM> would not be excessively stretched or deformed, and thus the support layer <NUM> and the conductive layer <NUM> are prevented from breakage; at the same time, it would be helpful to increase of binding strength between the support layer <NUM> and the conductive layer <NUM> without detaching from each other. Therefore, the positive current collector <NUM> could have higher mechanical stability and operating stability, so that the battery could have higher electrochemical performance, such as longer cycle life.

Preferably, the support layer <NUM> has a Young's modulus E satisfying 4GPa ≤ E ≤ 20GPa. This allows the support layer <NUM> have rigidity together with a certain ability to withstand deformation. As a result, the positive current collector <NUM> have a flexibility during winding and application, and is prevented from breakage.

The Young's modulus E of the support layer <NUM> may be measured by a method well known in the art. As an example, the method comprises cutting the support layer <NUM> into a sample of <NUM>×<NUM> and measuring the thickness h (µm) of the sample with a high-qualified micrometer; conducting a tensile test on a tensile test under normal temperature and pressure (<NUM>, <NUM>. 1MPa), where an initial position is set so that the sample length between the clamps is <NUM>, and the tensile speed is <NUM>/min; recording the load L(N) at which break occurs due to stretching, and the displacement y(mm) of the instrument; plotting a stress-strain curve on the basis of stress ε(GPa)=L/(<NUM>×h) and strain η=y/<NUM>, and taking the curve of the initial linear region to determine the slope of this curve, i.e. Young's modulus E. The tensile tester may be an Instron <NUM> tensile tester available from Instron, USA.

In some embodiments, preferably, the binding force between the support layer <NUM> and the conductive layer <NUM> may be F ≥ <NUM> N/m, more preferably F ≥ <NUM> N/m. The support layer <NUM> and the conductive layer <NUM> are firmly bonded, so that the support layer <NUM> may effectively support the conductive layer <NUM>, and that the burrs of the support layer <NUM> could cover the burrs of the conductive layer <NUM> more comprehensively during nail penetration. As a result, the nail penetration safety performance of the battery is improved.

The binding force F between the support layer <NUM> and the conductive layer <NUM> can be tested by a method known in the art. For example, the method comprises taking a positive current collector <NUM> where a conductive layer <NUM> is arranged on one side of the support layer <NUM> as a test sample with a width d of <NUM>; sticking a <NUM> double-sided tape evenly on a stainless steel plate, and then sticking the test sample evenly on the double-sided tape, with the positive current collector <NUM> being bonded to the double-sided tape; peeling the conductive layer <NUM> from the support layer <NUM> of the test sample continuously at a speed of <NUM>/ min under normal temperature and pressure (<NUM>, <NUM>. 1MPa) at an angle of <NUM>°; reading the maximum tensile force x (N) on the data diagram of tensile force vs. displacement, and calculating the binding force F (N/m) between the conductive layer <NUM> and the support layer <NUM> according to the formula F = x/d. The test may be carried out with an Instron <NUM> tensile tester available from Instron, USA.

In some embodiments, the support layer <NUM> may adopt one or more of polymer materials and polymer-based composite materials. Since polymers and polymer-based composites have a density that is significantly lower than that of metals, the positive current collector <NUM> could have a significantly reduced weight as compared with the existing metal current collectors. As a result, the weight energy density of the battery is increased.

In some embodiments, the polymers are, for example, one or more selected from polyamides, polyimides, polyesters, polyolefins, polyalkynes, siloxane polymers, polyethers, polyols, polysulfones, polysaccharide polymers, amino acid polymers, poly(sulphur nitride), aromatic ring polymers, aromatic heterocyclic polymers, epoxy resins, phenolic resins, and the derivatives, cross-linked products and copolymers of the above mentioned materials.

In some embodiments, polyamide polymers are for example polycaprolactam (commonly known as nylon <NUM>), polyhexamethylene adipamide (commonly known as nylon <NUM>), poly-p-phenylene terephthamide (PPTA), and poly-m-phenylene isophthalamide (PMIA); polyester polymers are for example polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), and polycarbonate (PC); polyolefin polymers are for example polyethylene (PE), polypropylene (PP), poly-propylene-ethylene (PPE); derivatives of polyolefin polymers are such as polyvinyl alcohol (PVA), polystyrene (PS), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTEE), and poly(sodium-p-styrenesulfonate) (PSS); polyalkyne polymers are for example polyacetylene (PA); the siloxane polymers are for example silicone rubber; polyether polymers are for example polyoxymethylene (POM), polyphenylene oxide (PPO), and polyphenylene sulfide (PPS); polyol polymers are for example polyethylene glycol (PEG); polysaccharide polymers are for example cellulose and starch; amino acid polymers are for example proteins; aromatic ring polymers are for example polyphenyl and polyparaphenylene; aromatic heterocyclic polymers are for example polypyrrole (PPy), polyaniline (PAN), polythiophene (PT), and polypyridine (PPY); a copolymer of polyolefin polymers and the derivatives thereof is for example acrylonitrile-butadiene-styrene copolymer (ABS).

The polymer-based composites may include one or more of the above-mentioned polymers and additives. The additives can adjust the volume resistivity, elongation at break, and Young's modulus of the polymers.

In some embodiments, the additives may include one or more of metallic materials and inorganic non-metallic materials. The metal materials are, for example, one or more selected from aluminum, aluminum alloy, copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, iron, iron alloy, silver, and silver alloy. The inorganic non-metallic materials are, for example, one or more selected from carbon-based materials, aluminum oxide, silicon dioxide, silicon nitride, silicon carbide, boron nitride, silicates, and titanium oxide, and are for example one or more selected from glass materials, ceramic materials and ceramic composites. The aforementioned carbon-based materials are, for example, one or more selected from graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the additives may be a metal-coated carbon-based materials, for example, one or more selected from nickel-coated graphite powder and nickel-coated carbon fiber.

Preferably, the support layer <NUM> adopts one or more selected from insulating polymer materials and insulating polymer-based composite materials. The support layer <NUM> has a relatively high volume resistivity that may be up to <NUM>×<NUM><NUM> Ω•m or more. Thus, the safety performance of the battery is further improved.

More preferably, the support layer <NUM> may include one or more selected from polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), poly(sodium-p-styrenesulfonate) (PSS), and polyimide (PI).

By adjusting the chemical composition, molecular weight and distribution thereof, chain structure and chain construction, aggregation structure, phase structure, additives, and the like of the polymer materials, the support layer <NUM> may have a predetermined volume resistivity, elongation at break and Young's modulus, so as to improve the safety performance and electrochemical performance of the battery.

In some embodiments, the support layer <NUM> may be a single-layer structure as shown in <FIG>, or may be a composite layer structure having two or more layers, such as two layers, three layers, and four layers.

The positive current collector <NUM> shown in <FIG> is an example of positive current collector in which the support layer <NUM> has a composite layer structure. Referring to <FIG>, the support layer <NUM> is a composite layer structure formed by stacking a first sub-layer <NUM>, a second sub-layer <NUM>, and a third sub-layer <NUM>. The support layer <NUM> having the composite layer structure has a first surface 101a and a second surface 101b opposite to each other, and the conductive layer <NUM> is laminated on the first surface 101a and the second surface 101b of the support layer <NUM>. Of course, the conductive layer <NUM> may be arranged only on the first surface 101a of the support layer <NUM>, or only on the second surface 101b of the support layer <NUM>.

Under the circumstance that the support layer <NUM> is a composite layer structure having two or more layers, each sub-layer has the same or different materials.

In the positive current collector <NUM> of the present application, the conductive layer <NUM> has a thickness D<NUM> satisfying <NUM> ≤ D<NUM> ≤ <NUM>. For example, the conductive layer <NUM> may have a thickness D<NUM> of <NUM> or less, <NUM> or less, <NUM> or less, <NUM> or less, <NUM> or less, or <NUM> or less, and a thickness D<NUM> of <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, or <NUM> or more. Preferably, <NUM> ≤ D<NUM> ≤ <NUM>.

The conductive layer <NUM> has a small thickness, and thus when the battery undergoes abnormal conditions such as nail penetration, the conductive layer <NUM> would generate significantly reduced burrs as compared with the existing metal current collectors. In addition, since a support layer <NUM> is disposed and the conductive layer <NUM> has a larger tensile sheet resistance growth rate during nail penetration, the positive current collector <NUM> and the positive electrode plate may have a large short-circuit resistance. Accordingly, the nail penetration safety performance of the battery is improved.

The conductive layer <NUM> having an appropriate thickness may ensure good electrical conductivity and current collecting performance of the positive current collector <NUM>, thereby rendering the battery to have good electrochemical performance, and at the same time, may ensure lower weight of the positive current collector <NUM>, thereby rendering the battery to have higher weight energy density. The conductive layer <NUM>, owing to the thickness D<NUM> thereof, is difficult to be damaged during the processing of the positive current collector <NUM> and its use in the battery, so that the positive current collector <NUM> has good mechanical stability and operating stability together with relatively long service life.

In some embodiments, the conductive layer <NUM> has a volume resistivity of from <NUM>×<NUM>-<NUM> Ω·m to <NUM>×<NUM>-<NUM> Ω·m. Under the condition that the conductive layer <NUM> has a volume resistivity falling within the appropriate range, the battery would have a relatively large short-circuit resistance when undergoing abnormal conditions such as nail penetration, meanwhile, the battery would have low impedance and reduced polarization because the positive current collector <NUM> would have good conductivity and current collecting performance. As a result, the battery would have higher safety performance together with higher electrochemical performance.

Further, the conductive layer <NUM> has a volume resistivity of preferably from <NUM>×<NUM>-<NUM> Ω·m to <NUM>×<NUM>-<NUM> Ω·m.

The conductive layer <NUM> has a volume resistivity ρ of ρ=RS × d, where ρ is in Ω•m, RS is the sheet resistance of the conductive layer <NUM> in Q, and d is the thickness of the conductive layer <NUM> in m. The sheet resistance RS of the conductive layer <NUM> is detected by means of a four-probe method. The exemplary method is conducted on a RTS-<NUM> double-electric four-probe tester with the test environment of <NUM>±<NUM>, <NUM>. 1MPa, and relative humidity ≤ <NUM>%. The test is performed by cleaning the surface of the positive electrode collector <NUM> as a sample, then placing it horizontally on the test bench; putting down the four probes so that the probes are in good contact with the surface of the conductive layer <NUM> of the sample; and then calibrating the current range of the sample under automatic test mode, so as to measure the sheet resistance under an appropriate current measuring range; collecting <NUM> to <NUM> data points of the same sample for data measurement accuracy and error analysis; and taking the average value as the sheet resistance of the conductive layer <NUM>.

The conductive layer <NUM> includes a metal material. The metal material is, preferably, one or more selected from aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, more preferably one or more selected from aluminum, aluminum alloy, nickel, nickel alloy, titanium and silver. Aluminum alloy may be an aluminum-zirconium alloy. Element aluminum is present in the aluminum alloy in a weight percentage content of preferably <NUM> wt% or more. Nickel alloy may be a nickel-copper alloy.

The conductive layer <NUM> may also include one or more selected from a carbon-based conductive material and a conductive polymer material. The one or more of the carbon-based conductive material and the conductive polymer material are present in the conductive layer <NUM> in a weight percentage of preferably <NUM> wt% or less.

The carbon-based conductive material may comprise one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

The conductive polymer material may comprise one or more of poly(sulphur nitride), aliphatic conjugated polymers, aromatic ring conjugated polymers, and aromatic heterocyclic conjugated polymers. The aliphatic conjugated polymer is, for example, polyacetylene. The aromatic ring conjugated polymer is, for example, polyphenyl, polynaphthalene, and polyphenyl is for example polyparaphenylene. The aromatic heterocyclic conjugated polymer is, for example, polypyrrole, polyaniline, polythiophene, and polypyridine. The conductivity of the conductive polymer material may also be improved by modification of doping.

<FIG> schematically show a positive current collector <NUM> respectively. Referring to <FIG>, the positive current collector <NUM> may optionally further include a protective layer <NUM>. Specifically, the protective layer <NUM> may be arranged between the conductive layer <NUM> and the support layer <NUM>. Alternatively, the protective layer <NUM> may be arranged on the surface of the conductive layer <NUM> facing away from the support layer <NUM>. Alternatively, a protective layer <NUM> may be arranged either between the conductive layer <NUM> and the support layer <NUM> or on the surface of the conductive layer <NUM> facing away from the support layer <NUM>.

The protective layer <NUM> can protect the conductive layer <NUM> from damages such as chemical corrosion or mechanical damage, and can ensure the operating stability and service life of the positive current collector <NUM> so as to be helpful to the safety performance and electrochemical performance of the battery. In addition, the protective layer <NUM> can also enhance the mechanical strength of the positive current collector <NUM>.

In some embodiments, the protective layer <NUM> may include one or more selected from metal, metal oxide, and conductive carbon.

The metal may include one or more selected from nickel, chromium, nickel-based alloys, and copper-based alloys. The nickel-based alloy is an alloy formed by adding one or more other elements to pure nickel base, and preferably is a nickel-chromium alloy. Nickel-chromium alloy is an alloy formed from metallic nickel and metallic chromium. Optionally, the weight ratio of nickel to chromium in the nickel-chromium alloy is from <NUM>:<NUM> to <NUM>:<NUM>, such as <NUM>:<NUM>. The copper-based alloy is an alloy formed by adding one or more other elements to pure copper base, and preferably is a nickel-copper alloy. Optionally, the weight ratio of nickel to copper in the nickel-copper alloy is from <NUM>:<NUM> to <NUM>:<NUM>, such as <NUM>: <NUM>.

The metal oxide may include one or more selected from aluminum oxide, cobalt oxide, chromium oxide, and nickel oxide.

The conductive carbon may include one or more selected from graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, and preferably includes one or more selected from carbon black, carbon nanotubes, acetylene black, and graphene.

In some embodiments, the protective layer <NUM> may include one or more selected from nickel, chromium, nickel-based alloys, copper-based alloys, aluminium oxide, cobalt oxide, chromium oxide, nickel oxide, graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some preferred embodiments, the protective layer <NUM> may adopt metal and/or metal oxide. That is, a metal protective layer, or a metal oxide protective layer, or a metal and metal oxide composite protective layer is/are arranged on the conductive layer <NUM>. The protective layer <NUM> has high corrosion resistance, high hardness, and large specific surface area, and thus have high comprehensive performance.

As some examples, referring to <FIG> and <FIG>, the positive current collector <NUM> includes a support layer <NUM>, a conductive layer <NUM> and a protective layer <NUM> that are laminated, wherein the support layer <NUM> has a first surface 101a and a second surface 101b opposite to each other in its thickness direction, the conductive layer <NUM> is laminated on at least one of the first surface 101a and the second surface 101b of the support layer <NUM>, and the protective layer <NUM> is laminated on the surface of the conductive layer <NUM> facing away from the support layer <NUM>.

The protective layer <NUM> arranged on the surface of the conductive layer <NUM> facing away from the support layer <NUM> (hereinafter referred to as an upper protective layer) protects the conductive layer <NUM> from chemical corrosion and mechanical damage. In particular, the metal protective layer or metal oxide protective layer can not only protect the conductive layer <NUM>, but also improve the interface between the positive current collector <NUM> and the positive active material layer, reduce the interface resistance, and increase the binding force between the positive current collector <NUM> and the positive active material layer. As a result, the polarization of the plates is reduced and the electrochemical performance of the battery is improved.

As another example, referring to <FIG>, the positive current collector <NUM> includes a support layer <NUM>, a conductive layer <NUM> and a protective layer <NUM> that are laminated, wherein the support layer <NUM> has a first surface 101a and a second surface 101b opposite to each other in its thickness direction, the conductive layer <NUM> is laminated on at least one of the first surface 101a and the second surface 101b of the support layer <NUM>, and the protective layer <NUM> is laminated between the conductive layer <NUM> and the support layer <NUM>.

The protective layer <NUM> arranged between the conductive layer <NUM> and the support layer <NUM> (hereinafter referred to as a lower protective layer) has the two opposite surfaces attached to the conductive layer <NUM> and the support layer <NUM> respectively. The lower protective layer can improve the support and protection effect on the conductive layer <NUM>. At the same time, it can also serve as protection against chemical corrosion and mechanical damage. The lower protective layer also improves the binding force between the conductive layer <NUM> and the support layer <NUM> and prevents the conductive layer <NUM> from separating from the support layer <NUM>. In particular, the lower protective layer of metal oxide or metal has high hardness and large specific surface area, and thus can have better protection effects as mentioned above. More preferably, the lower protective layer is a metal oxide protective layer. Because the metal oxide protective layer has a larger specific surface area and higher hardness, the interface binding force between the support layer <NUM> and the conductive layer <NUM> is further improved.

As still another example, referring to <FIG> and <FIG>, the positive current collector <NUM> includes a support layer <NUM>, a conductive layer <NUM> and a protective layer <NUM> that are laminated, wherein the support layer <NUM> has a first surface 101a and a second surface 101b opposite to each other in its thickness direction, the conductive layer <NUM> is laminated on at least one of the first surface 101a and the second surface 101b of the support layer <NUM>, and the protective layer <NUM> is arranged either between the conductive layer <NUM> and the support layer <NUM> or on the surface of the conductive layer <NUM> facing away from the support layer <NUM>.

Arranging the protective layer <NUM> on both surfaces of the conductive layer <NUM> can protect the conductive layer <NUM> more sufficiently. It can be understood that the protective layers <NUM> on the two surfaces of the conductive layer <NUM> may have the same or different material(s), and may have the same or different thickness(es).

In some embodiments, the protective layer <NUM> has a thickness D<NUM> satisfying <NUM> ≤ D<NUM> ≤ <NUM>, and D<NUM> ≤ <NUM>. For example, the protective layer <NUM> may have a thickness D<NUM> preferably of <NUM> or less, <NUM> or less, <NUM> or less, <NUM> or less, <NUM> or less, <NUM> or less, <NUM> or less, <NUM> or less, <NUM> or less, <NUM> or less, <NUM> or less, <NUM> or less, and <NUM> or less, and of <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, and <NUM> or more. Preferably, <NUM> ≤ D<NUM> ≤ <NUM>. Preferably, <NUM> ≤ D<NUM> ≤ <NUM>.

The protective layer <NUM>, due to the thickness thereof, is suitable for effectively protecting the conductive layer <NUM>, and at the same time, can ensure the higher energy density of the battery.

In some embodiments, when protective layers <NUM> are arranged on both surfaces of the conductive layer <NUM>, the protective layer <NUM> on the surface of the conductive layer <NUM> facing away from the support layer <NUM> (upper protective layer) has a thickness of Da, <NUM> ≤ Da ≤ <NUM> and Da ≤ <NUM>. 1D<NUM>; the protective layer <NUM> between the conductive layer <NUM> and the support layer <NUM> (lower protective layer) has a thickness of Db, <NUM> ≤ Db ≤ <NUM>, and Db ≤ <NUM>. Preferably, Da > Db. Thus, the protective layer <NUM> has a good protection effect on the conductive layer <NUM> against chemical corrosion and mechanical damage, and can enable the battery to have higher energy density. More preferably, <NUM>. 5Da ≤ Db ≤ <NUM>. The protective layer <NUM> has better protection effects as mentioned above.

The conductive layer <NUM> may be formed on the support layer <NUM> by at least one means selected from mechanical rolling, bonding, vapor deposition, chemical plating, and electroplating, with vapor deposition or electroplating being preferred. In this way, the conductive layer <NUM> and the support layer <NUM> may bind tightly.

For example, the conductive layer <NUM> is formed on the support layer <NUM> by a vapor deposition method. The conductive layer <NUM> and the support layer <NUM> have a higher binding force, which is beneficial to improving the mechanical stability, operating stability and safety performance of the positive current collector <NUM>. By reasonably adjusting the conditions of the vapor deposition process, such as the deposition temperature, the deposition rate, and the atmosphere conditions of the deposition chamber, the conductive layer <NUM> may have a sheet resistance growth rate satisfying the above mentioned requirement when the positive current collector <NUM> is stretched, so as to improve the safety performance and electrochemical performance of the positive current collector <NUM>.

The vapor deposition method is preferably a physical vapor deposition method. The physical vapor deposition method is preferably at least one of an evaporation method and a sputtering method. The evaporation method is preferably at least one of a vacuum evaporation method, a thermal evaporation method, and an electron beam evaporation method, and the sputtering method is preferably a magnetron sputtering method.

As an example, the conductive layer <NUM> can be formed by a vacuum evaporation method, including placing the support layer <NUM>, having being subjected to surface cleaning treatment, in a vacuum coating chamber; and melting and evaporating a high-purity metal wire in the metal evaporation chamber at a high temperature of from <NUM> to <NUM>, wherein the evaporated metal passes through a cooling system in the vacuum coating chamber, and is finally deposited on the support layer <NUM> to form a conductive layer <NUM>.

The protective layer <NUM> may be formed on the conductive layer <NUM> by at least one means selected from a vapor deposition method, an in-situ forming method, and a coating method. The vapor deposition method may be one as described above. The in-situ forming method is preferably an in-situ passivation method, a method of forming a metal oxide passivation layer in situ on the metal surface. The coating method is preferably at least one of roll coating, extrusion coating, knife coating, and gravure coating.

Preferably, the protective layer <NUM> is formed on the conductive layer <NUM> by means of at least one selected from a vapor deposition method and an in-situ forming method, which is beneficial to making the conductive layer <NUM> and the protective layer <NUM> have a higher binding force, so that the protective layer <NUM> may better protect the positive current collector <NUM> and ensure the higher operating performance of the positive current collector <NUM>.

When a protective layer <NUM> (i.e. a lower protective layer) is arranged between the conductive layer <NUM> and the support layer <NUM>, the lower protective layer <NUM> may be formed on the support layer <NUM> first, and then the conductive layer <NUM> is formed on the lower protective layer. The lower protective layer may be formed on the support layer <NUM> by at least one means selected from a vapor deposition method and a coating method. The vapor deposition is preferred for it is beneficial to obtaining a higher binding force between the lower protective layer and the support layer <NUM>. The conductive layer <NUM> can be formed on the lower protective layer by at least one means selected from mechanical rolling, bonding, vapor deposition, chemical plating, and electroplating. At least one of vapor deposition and electroplating is preferred for they are beneficial to obtaining a higher binding force between the lower protective layer and the conductive layer <NUM>. The vapor deposition method and the coating method may respectively be the vapor deposition method and the coating method as described above.

In some embodiments, the binding force F<NUM> between the conductive layer <NUM> and the protective layer <NUM> satisfies F<NUM> ≥ <NUM> N/m, preferably F<NUM> ≥ <NUM> N/m.

In some embodiments, when the protective layer is disposed between the conductive layer <NUM> and the support layer <NUM>, the binding force between the protective layer <NUM> and the support layer <NUM> satisfies F<NUM> ≥ 100N/m, preferably F<NUM> ≥ 400N/m.

The binding force F<NUM> between the conductive layer <NUM> and the protective layer <NUM> and the binding force F<NUM> between the protective layer <NUM> and the support layer <NUM> may be measured with reference to the above-mentioned method for testing the binding force F between the support layer and the conductive layer.

A second aspect of the application provides a positive electrode plate, including a positive current collector <NUM> and a positive active material layer that are laminated, wherein the positive current collector <NUM> is any one of the positive current collectors 10according to the first aspect of the application.

Since the positive electrode plate <NUM> of the present application adopts the positive current collector <NUM> of the first aspect of the present application, it has a higher weight energy density and better nail penetration safety performance and electrochemical performance as compared with the existing positive electrode plate.

<FIG> shows an example of positive electrode plate <NUM>. As shown in <FIG>, the positive electrode plate <NUM> includes a support layer <NUM>, a conductive layer <NUM>, and a positive active material layer <NUM> that are laminated, wherein the support layer <NUM> includes two opposite surfaces, the conductive layer <NUM> is laminated on both surfaces of the support layer <NUM>, and the positive active material layer <NUM> is laminated on the surface of the conductive layer <NUM> facing away from the support layer <NUM>.

<FIG> shows another example of positive electrode plate <NUM>. As shown in <FIG>, the positive electrode plate <NUM> includes a support layer <NUM>, a conductive layer <NUM>, and a positive active material layer <NUM> that are laminated, wherein the support layer <NUM> includes two opposite surfaces, the conductive layer <NUM> is laminated either one of the two surfaces of the support layer <NUM>, and the positive active material layer <NUM> is laminated on the surface of the conductive layer <NUM> facing away from the support layer <NUM>.

The positive active material layer <NUM> may comprise a positive electrode active material known in the art, which allows reversible intercalation/deintercalation of ions.

For example, the positive active material for lithium ion secondary batteries may comprise lithium transition metal composite oxides, where the transition metal may be one or more selected from Mn, Fe, Ni, Co, Cr, Ti, Zn, V, Al, Zr, Ce, and Mg. The lithium transition metal composite oxide may also be doped with elements having high electronegativity, such as one or more of S, F, Cl, and I. This enables the positive active material to have higher structural stability and electrochemical performance. As an example, the lithium transition metal composite oxide is, for example, one or more selected from LiMn<NUM>O<NUM>, LiNiO<NUM>, LiCoO<NUM>, LiNi<NUM>-yCoyO<NUM> (<NUM><y<<NUM>), LiNiaCobAl<NUM>-a-bO<NUM> (<NUM><a<<NUM>, <NUM><b<<NUM>, and <NUM><a+b<<NUM>), LiMn<NUM>-m-nNimConO2 (<NUM><m<<NUM>, <NUM><n<<NUM>, and <NUM><m+n<<NUM>), LiMPO<NUM> (M may be one or more of Fe, Mn, Co), and Li<NUM>V<NUM>(PO<NUM>)<NUM>.

In some embodiments, the positive active material layer <NUM> may further include a conductive agent. As an example, the conductive agent may be one or more selected from graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the positive active material layer <NUM> may further include a binder. As an example, the binder may be one or more selected from styrene butadiene rubber (SBR), water-based acrylic resin, carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

The positive electrode plate <NUM> may be prepared according to conventional methods in the art. Usually the positive active material, an optional conductive agent, and a binder are dispersed in a solvent (such as N-methylpyrrolidone, referred to as NMP) to form a uniform positive electrode slurry; then the positive current collector <NUM> is coated with the positive electrode slurry, and after drying, the positive electrode plate <NUM> is obtained.

A third aspect of the present application provides a battery, including a positive electrode plate, a negative electrode plate, a separator and an electrolyte, wherein the positive electrode plate is any one of the positive electrode plates according to the second aspect of the application.

Examples of batteries may be a primary battery or a secondary battery. Particular examples may include, but are not limited to, lithium ion secondary batteries, lithium primary batteries, sodium ion batteries, magnesium ion batteries, and the like.

The battery of the present application adopts the positive electrode plate according to the second aspect of the present application, and thus can have higher weight energy density, good nail penetration safety performance, and electrochemical performance.

The negative electrode plate may include a negative current collector and a negative active material layer arranged on the negative current collector.

The negative electrode current collector may be metal foil, carbon-coated metal foil and porous metal foil. The negative electrode current collector may comprise one or more selected from copper, copper alloy, nickel, nickel alloy, iron, iron alloy, titanium, titanium alloy, silver, and silver alloy.

The negative electrode active material layer may adopt a negative electrode active material known in the art, which allows reversible intercalation/deintercalation of ions. For example, the negative active material for lithium ion secondary batteries may include one or more selected from metallic lithium, natural graphite, artificial graphite, mesophase micro-carbon spheres (abbreviated as MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO<NUM>, lithium titanate of spinel structure, and Li-Al alloy.

Optionally, the negative active material layer may further include a binder. As an example, the binder may be one or more selected from styrene-butadiene rubber (SBR), water-based acrylic resin, carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

Optionally, the negative active material layer may further include a conductive agent. As an example, the conductive agent may be one or more selected from of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

The negative electrode may be prepared according to conventional methods in the art. Generally, the negative electrode active material, an optional conductive agent, a binder, a thickening agent, and a dispersing agent are dispersed in a solvent to form a uniform negative electrode slurry, wherein the solvent may be NMP or deionized water; then a negative current collector was coated with the negative electrode slurry, and after drying, the negative electrode plate is obtained.

The separator is not specifically limited, and may be any well-known porous separator having electrochemical and chemical stability. For example, it may be single-layer or multi-layer films, which is one or more selected from glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

The electrolyte may be selected from solid electrolytes and electrolyte solutions. The electrolyte solutions includes an organic solvent and an electrolyte salt. The organic solvent, as a medium for transporting ions in an electrochemical reaction, may be organic solvents used for battery electrolytes well-known in the art. The electrolyte salt, as a source donating ions, may be an electrolyte salt used for the electrolyte of a battery well-known in the art.

For example, the organic solvent used in lithium ion secondary batteries may comprise one or more, and preferably more than two, selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethylene propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF ), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), <NUM>,<NUM>-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

For example, the electrolyte salt used for lithium ion secondary batteries may comprise one or more selected from LiPF<NUM> (lithium hexafluorophosphate), LiBF<NUM> (lithium tetrafluoroborate), LiClO<NUM> (lithium perchlorate), LiAsF<NUM> (lithium hexafluoroarsenate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethane sulfonimide)), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluoro (oxalato)borate), LiBOB (lithium bis(oxalate)borate), LiPO<NUM>F<NUM> (lithium difluorophosphate), LiDFOP (lithium difluorodi(oxalato)phosphate) and LiTFOP (lithium tetrafluoro(oxalato)phosphate).

In some embodiments, the battery may include an outer package for encapsulating the positive electrode plate, the negative electrode plate, and the electrolyte. As an example, the positive electrode plate, the negative electrode plate and the separator may form an electrode assembly of laminated structure or wound structure by laminating or winding, and the electrode assembly is encapsulated in an outer package. The electrolyte may be an electrolyte solution, in which the electrode assembly is immersed. The number of electrode assemblies in the battery may be one or several, and may be adjusted according to requirements.

In some embodiments, the outer packaging of the battery may be a soft bag, such as a pouch-type soft bag. The soft bag may be made of plastic including for example one or more selected from polypropylene PP, polybutylene terephthalate PBT, polybutylene succinate PBS and the like. The outer packaging of the battery may also be a hard case, such as an aluminum case.

The present application has no particular limitation to the shape of the battery, which thus may be cylindrical, square or other arbitrary shapes. <FIG> shows an example of the battery <NUM> having a square structure.

In some embodiments, the battery can be assembled into a battery module. The number of secondary batteries included in the battery module may be more than one, and the particular number may be adjusted according to the application and capacity of the battery module.

<FIG> shows an example of the battery module <NUM>. Referring to <FIG>, in the battery module <NUM>, a plurality of secondary batteries <NUM> may be arranged in sequence along the length direction of the battery module <NUM>. Of course, they may be arranged in any other manner. Furthermore, a plurality of secondary batteries <NUM> can be fixed by fasteners.

The battery module <NUM> may optionally include a housing having an accommodating space, in which a plurality of secondary batteries <NUM> are accommodated.

In some embodiments, the above-mentioned battery modules may also be assembled into a battery pack, and the number of battery modules included in the battery pack may be adjusted according to the application and capacity of the battery pack.

<FIG> and <FIG> show an example of the battery pack <NUM>. Referring to <FIG> and <FIG>, the battery pack <NUM> may include a battery case and a plurality of battery modules <NUM> provided in the battery case. The battery case includes an upper case body <NUM> and a lower case body <NUM>. The upper case body <NUM> may cover the lower case body <NUM> to form a closed space for accommodating the battery module <NUM>. A plurality of battery modules <NUM> may be arranged in the battery case in arbitrary manner.

A fourth aspect of the present application provides an apparatus including the battery according to the third aspect of the present application, wherein the battery provides power for the apparatus. The apparatus may be, but is not limited to, mobile apparatuses (such as mobile phones, notebook computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf vehicles, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc..

The apparatus, according to its using requirements, may include a battery, a battery module, or a battery pack.

<FIG> shows an example of the apparatus. The apparatus is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the apparatus for high power and high energy density of the battery, a battery pack or a battery module can be used.

As another example, the apparatus may be a mobile phone, a tablet computer, a notebook computer etc. The apparatus is generally required to be thin and light, and may include the battery as a power source.

The disclosure is described in more details through the following examples, which are only for illustrative purpose.

Unless otherwise stated, all parts, percentages, and ratios reported in the examples below are based on weight, all the reagents used in the examples are commercially available or synthesized according to conventional methods and can be directly used without further treatment, and all the instruments used in the examples are commercially available.

A support layer having a predetermined thickness was selected to be subjected to surface cleaning treatment. The support layer after the surface cleaning treatment was placed in a vacuum plating chamber. The high-purity aluminum wire in the metal evaporation chamber was melted to evaporate under a high temperature of from <NUM> to <NUM>. The evaporated metal passed through the cooling system of the vacuum plating chamber, and was finally deposited on the two surfaces of the support layer to form a conductive layer.

A positive electrode active material LiNi<NUM>/<NUM>Co<NUM>/<NUM>Mn<NUM>/<NUM>O<NUM> (referred to as NCM333), a conductive carbon black, and a binder polyvinylidene fluoride (PVDF) at a weight ratio of <NUM>:<NUM>:<NUM> were stirred to mix in an appropriate amount of N-methylpyrrolidone (NMP), so as to form a uniform positive electrode slurry; the positive current collector was coated with the positive electrode slurry; and after processes of drying etc., the positive electrode plate was obtained.

The preparation of the conventional positive electrode plate was the same as that of the positive electrode plate of the present application with the exception that an aluminum foil of <NUM> was used.

A copper foil having a thickness of <NUM> was used.

Graphite as a negative active material, conductive carbon black, sodium carboxymethyl cellulose (CMC) as a thickener, and styrene butadiene rubber emulsion (SBR) as a binder at a weight ratio of <NUM>:<NUM>:<NUM>:<NUM> were stirred to mix in an appropriate amount of deionized water, so as to form a uniform negative electrode slurry; the negative current collector was coated with the negative electrode slurry, and after processes of drying etc., a negative electrode plate was obtained.

Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of <NUM>:<NUM> were uniformly mixed to obtain an organic solvent, and then <NUM> mol/L of LiPF<NUM> was uniformly dissolved in organic solvent as prepared above.

The positive electrode plate, a separator, and the negative electrode plate were laminated in sequence, and then were wound into an electrode assembly, which was placed into an outer package, wherein the separator, as a composite film of PP/PE/PP, was arranged between the positive and the negative electrode plate to isolate them; the electrolyte solution as prepared above was injected into the electrode assembly; and after being subjected to the processes of sealing, standing, hot-cold pressing, forming, etc., a lithium-ion battery was obtained.

The volume resistivity of the support layer, the sheet resistance growth rate T<NUM> of the conductive layer when the tensile strain ε of the positive current collector is <NUM>%, the sheet resistance growth rate T<NUM> of the conductive layer when the tensile strain ε of the positive current collector is <NUM>%, and the Young's modulus E of the support layer were respectively tested by test methods as described above.

At <NUM>, the lithium ion secondary battery was charged to <NUM>. 2V at a constant current rate of 1C, next charged to a current less than or equal to <NUM>. 05C at a constant voltage, and then was discharged to <NUM>. 8V at a constant current rate of 1C, which was a charge-discharge cycle. The discharge capacity as above was the discharge capacity of the first cycle. The battery was subjected to <NUM> charge-discharge cycles according to the above method, and the discharge capacity of the 1000th cycle was recorded.

The capacity retention rate of the battery for <NUM> cycles of 1C/1C at <NUM> was measured with reference to the above method.

At <NUM>, the lithium ion battery was charged to <NUM>. 2V at a constant current rate of 1C, and then was charged to a current less than or equal to <NUM>. 05C at a constant voltage. Afterwards, the lithium ion battery was penetrated through with a steel nail having a diameter of <NUM> at a speed of <NUM>/s, and was monitored for its temperature and voltage change with the steel nail being retained in the lithium ion battery.

Test of the battery temperature: the test was performed by attaching sensing wires to the front and back surfaces through which the nail penetrated at their geometric centers by means of a Multi-Channel Thermometer. After nail penetration, a battery temperature tracking test was conducted for five minutes, and then the battery temperature at the end of five minutes was recorded as the value of temperature rise of battery.

Test of battery voltage: The positive and negative electrodes of the battery to be nail-penetrated were connected to the measuring terminal of an Internal Resistance Meter. After nail penetration, a battery voltage tracking test was conducted for five minutes, and then the battery voltage at the end of five minutes was recorded.

Electrochemical performance of the positive current collectors according to the present application and effect thereof on the nail penetration safety performance of batteries.

In Table <NUM>, "*" denotes those electrode plates in which the protective layer(s) was arranged on the positive electrode plate <NUM>; and "**" denotes those electrode plates in which the protective layer(s) was arranged on the positive electrode plate <NUM>.

The batteries adopting the positive current collectors according to the present application had good cycle life, which were equivalent to those batteries adopting conventional positive current collectors in terms of cycle performance. This indicated that the positive current collectors according to the present application would not bring about a significantly adverse effect on the electrochemical performance of the positive electrode plates and the batteries. Especially, the batteries adopting positive current collectors provided with a protective layer, had further improved capacity retention rate for <NUM> cycles of 1C/1C, indicating that the batteries exhibited better reliability.

In addition, by adopting the positive current collector according to the present application, the lithium ion batteries had greatly improved nail penetration safety performance. From the data shown in Table <NUM>, it could be seen that, at the moment of nail penetration, the battery adopting conventional positive current collector would undergo a sudden temperature rise of <NUM> and a sudden voltage drop to zero. This indicates that, at the moment of nail penetration, the battery would undergo an internal short circuit, which generates a lot of heat, and in turn the battery would undergo instant thermal runaway destruction, resulting in failure. In the test of nail penetration, the batteries adopting the positive current collectors according to the present application had a temperature rise that was controlled at around <NUM> or below <NUM>, and were kept at basically stable battery voltage, so that the batteries could operate in a normal way.

As can be seen, under the circumstances that the batteries undergone an internal short circuit, the positive current collectors according to the present application could greatly reduce the heat generated from short-circuit, and thus could improve the safety performance of the batteries. In addition, the positive current collectors according to the present application could limit the impact of the short-circuit damage to the batteries in a "point" area, forming "Point Break" only, without affect the normal operation of the battery in a short time.

From the data shown in Tables <NUM> and <NUM>, it can be seen that since the comparative positive current collectors <NUM> and <NUM> had the sheet resistance growth rates of the conductive layers of T<NUM><<NUM>% when having a tensile strain of greater than or equal to <NUM>%, the batteries adopting the comparative positive current collectors <NUM> or <NUM>, when undergoing abnormal conditions such as nail penetration, had a sharp temperature rise of higher than <NUM> and a sharp voltage drop to zero. This showed that at the moment of nail penetration, the battery had an internal short circuit and thus generated a lot of heat. As a result, the battery undergone an instantly thermal runaway and damage, leading to failure.

In contrast, the positive current collectors according to the present application had the sheet resistance growth rate of the conductive layers of T<NUM> ≥ <NUM>% when having a tensile strain of greater than or equal to <NUM>%, the batteries adopting the positive current collectors according to the present application, when undergoing abnormal conditions such as nail penetration, had a temperature rise that may be controlled basically below <NUM>; and the battery had basically stable voltages, and thus could operate in a normal way.

It can be seen that under the condition that an internal short circuit in the battery occurs, the positive current collectors according to the examples of the present application could greatly reduce the heat generated from short-circuit, so as to improve the safety performance of the batteries. In addition, they could limit damage on the battery caused by short circuit to "points" area and thus formed "Point Break" only, without affecting the normal operation of the battery in a short time.

In Table <NUM>, the aluminum alloy had a composition of <NUM> wt% of aluminum and the balance of <NUM> wt% of zirconium.

The positive current collectors in Table <NUM> were subjected to an overcurrent test and samples for the overcurrent test were prepared by cutting the positive current collectors into a sheet of <NUM> in width; applying an active material layer of <NUM> width at the center of the sheet in the width direction and rolling it to obtain plates; cutting the rolled plates into strips of <NUM> × <NUM> along the width direction, <NUM> strips for each plate sample. During the test, the uncoated conductive areas on both sides of the plate sample were respectively connected to the positive and negative terminals of the Charging and Discharging Machine, and then by setting the Charging and Discharging Machine, a <NUM> A current flowed through the plate and the plate was kept at the current for <NUM>. If there was no fusing, it meant that the plate passed the test, otherwise, it means fail. Five samples as a group were tested, and the results of overcurrent test were shown in Table <NUM> below.

When the tensile strain of the positive current collectors was <NUM>%, the sheet resistance growth rate T<NUM> of the conductive layers was not more than <NUM>%, thus the positive electrode plates adopting such positive current collectors could have better conductivity after rolling. Otherwise, the conductivity of the positive electrode plates was poor, resulting in little practical value in battery products. Preferably, when the tensile strain of the positive current collector was <NUM>%, the sheet resistance growth rate of the conductive layer satisfied T<NUM>≤<NUM>%, more preferably T<NUM>≤<NUM>%.

In Table <NUM>, the weight percentage of the positive current collector referred to the weight percentage obtained by dividing the weight per unit area of the positive current collectors by the weight per unit area of the conventional positive current collectors.

As compared with the traditional positive collector of aluminum foil, the weight of the positive current collectors according to the present application were reduced to some extents, so that the weight energy density of the batteries could be improved.

Above described are only specific implementations of the present invention, but the protection scope of the present invention is not intended to be limited thereto.

Claim 1:
A positive current collector (<NUM>) comprising
a support layer (<NUM>) having two surfaces opposite to each other in a thickness direction of the support layer (<NUM>);
a conductive layer (<NUM>) arranged on at least one of the two surfaces of the support layer(<NUM>);
wherein the conductive layer (<NUM>) has a thickness D<NUM> satisfying <NUM> ≤ D<NUM> ≤ <NUM>, preferably <NUM> ≤ D<NUM> ≤ <NUM>; and
wherein the positive current collector (<NUM>) has a tensile strain of <NUM>% or more, and the conductive layer (<NUM>) has a sheet resistance growth rate of T<NUM> ≥<NUM>%, as determined according to the description,
the conductive layer (<NUM>) comprises one or more of selected from aluminum, aluminum alloy, nickel, nickel alloy, titanium, and silver.