Lithium battery and electrode plate structure

A lithium battery is provided. The lithium battery comprises an positive electrode plate having a first surface, a negative electrode plate having a second surface, a first thermal insulating layer and a separator. The first surface is opposite to the second surface. The thermal insulating layer is disposed on one of the first surface and the second surface. The thermal insulating layer is comprised of an inorganic material, a thermal activation material and a binder. The separator is disposed between the positive electrode plate and the negative electrode plate.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan application serial no. 99146137, filed Dec. 27, 2010. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND OF THE APPLICATION

1. Field of the Invention

The application relates to a battery, and particularly to a lithium battery.

2. Description of Related Art

Since one-time used battery does not full fill the requirement of the environmental protection, the battery system capable of being recharged is getting a lot of interests. With the rapid development and popularization of the portable electronic products, the lithium batteries which can repeat the cycle of discharging-and-recharging have the advantages of light weight, high voltage and high energy density so that the market demands on the lithium batteries increase. Comparing with the nickel-metal-hydride battery, the nickel-zinc battery and the nickel-cadmium battery, the lithium battery has the advantages of high working voltage, large energy density, light weight, long lifetime and good environmental protection and the lithium battery is one of the best batteries for being applied in the flexible battery in the future.

The lithium batteries are widely used in the so-called 3C products including computers (i.e. the information products), the communication products and the consumer electronics so that the demands on the performance of the lithium batteries, such as light weight, durability, high voltage, high energy density and safety, become high. Further, the developmental potential and the application of the lithium batteries in the light-weighted electromobile industry, electric motor car industry and large-sized electronic storage industry are high. However, the organic solvents (most of these organic solvents include the organic molecules having ester groups) with high-voltage endurance which is used in the lithium battery system is flammable. Also, the positive electrode/negative electrode activity substance with high capacitance would decompose to generate a great amount of heat while the temperature of the battery increases so that the heat generated while the lithium battery is not properly used can ignite the organic solvent and even lead to the explosion. Moreover, during the discharge process of the lithium battery, since the oxygen is expelled from the positive electrode material structure, the expelled oxygen reacts with the electrolyte, which leads to the increasing of the internal temperature and induces safety problem of the lithium battery.

SUMMARY OF THE INVENTION

The application provides a lithium battery capable of decreasing the conductivity while the temperature of the lithium battery increases.

The application provides a electrode plate structure capable of enhancing the safety for using the lithium battery.

The application provides a lithium battery comprising a positive electrode plate, a negative electrode plate, a first thermal insulating layer and a separator. The positive electrode plate has a first surface. The negative electrode plate has a second surface and the second surface is opposite to the first surface of the positive electrode plate. The first thermal insulating layer is located on one of the first surface and the second surface, wherein the first thermal insulating layer is comprised of an inorganic material, a thermal activation material and a binder. The separator is located between the positive electrode plate and the negative electrode plate.

The application further provides an electrode plate structure comprising an electrode plate and a thermal insulating layer. The electrode plate has a charging-discharging surface. The thermal insulating layer is located on the charging-discharging surface, wherein the thermal insulating layer is comprised of an inorganic material, a thermal activation material and a binder.

In order to make the aforementioned features and advantages of the application more comprehensible, embodiments accompanying figures are described in detail below.

DESCRIPTION OF EMBODIMENTS

FIG. 1is a schematic cross-sectional view of a portion of a lithium battery according to one embodiment of the present application. As shown inFIG. 1, a lithium battery100of the present embodiment comprises several positive electrode plates102, several negative electrode plates104, several separators108and an electrolyte110. The positive electrode plates102and the negative electrode plates104are alternatively arranged and are stacked on one another. Further, for a pair of one positive electrode plate102and one negative electrode plate104, there is one separator108disposed between the positive electrode plate102and the negative electrode plate104. Each of the separators108can be formed of, for example but not limited to, a porous structure and the porosity of the porous structure is about 40˜55%. Moreover, the holes of the porous structure uniformly distribute in the whole separator108. The positive electrode plates102, the separators108, the negative electrode plates104which are stacked on one another are soaked in the electrolyte110. On other words, the whole body of the battery is flood with the electrolyte110.

The material of the positive electrode plates102includes lithium mixed metal oxide, such as one selected from a group comprised of LiMnO2, LiMn2O4, LiCoO2, Li2Cr2O7, Li2CrO4, LiNiO2, LiFeO2, LiNixCo1-xO2(0<x<1), LiMPO4(M=transition metal), LiMn0.5Ni0.5O2, LiNixCoyMnzO2(x+y+z=1), LiNixCoyAlzO2(x+y+z=1), LiMc0.5Mn1.5O4and the combination thereof, wherein Mc is divalent metal.

The material of the negative electrode plates includes carbide and lithium alloy. The carbide can be selected from a group comprised of carbon powder, graphite, carbon fiber, carbon nanotubes and the combination thereof. In one embodiment of the present application, the carbide is carbon powder and the particle diameter of the carbon powder is about 1˜30 microns. In another embodiment, the material of the negative electrode plates104includes metal, such as LiAl, LiZn, Li3Bi, Li3Cd, Li3Sb, Li4Si, Li4.4Pb, Li4.4Sn, LiC6, Li3FeN2, Li2.6Co0.4N, Li2.6Cu0.4N and the combination thereof. Moreover, In another embodiment, the negative electrode plates104include metal-containing oxide, such as SnO, SnO2, GeO, GeO2, In2O, In2O3, PbO, PbO2, Pb2O3, Pb3O4, Ag2O, AgO, Ag2O3, Sb2O3, Sb2O4, Sb2O5, SiO, ZnO, CoO, NiO, FeO, TiO2, Li3Ti5O12or the combination thereof.

FIG. 1Ais a partial enlargement view of the cross-section of the lithium battery shownFIG. 1. More specifically, as shown inFIG. 1A, the lithium battery of the present embodiment further comprises a first thermal insulating layer106. That is, the positive electrode plate102is disposed to be opposite to the negative electrode plate104and the positive electrode plate102has a first surface102aopposite to the negative electrode plate104and the negative electrode plate104has a second surface104aopposite to the positive electrode plate102. On other words, the second surface104ais opposite to the first surface102aof the positive electrode plate102. Each of the first surface102aand the second surface104ais a charging-discharging surface of the electrode plate which the lithium ions diffuse into or out during the charging process and discharging process of the lithium battery.

The first thermal insulating layer106is located on one of the first surface102aand the second surface104a. The thickness of the first thermal insulating layer106is about 0.1˜20 microns. In the present embodiment, the first thermal insulating layer106is located on the first surface102aof the positive electrode plate102. However, the aforementioned arrangement does not limit the scope of the present application. As shown inFIG. 1B, a partial enlargement view of a cross-section of a lithium battery200according to another embodiment of the present application, the first thermal insulating layer106is disposed on the negative electrode plate104. That is, the first thermal insulating layer106can be disposed on either the first surface102aor the second surface104a.

Moreover,FIG. 1Cis a partial enlargement view of a cross-section of a lithium battery according to the other embodiment of the present application. As shown inFIG. 1C, the lithium battery300of the present embodiment further comprises a second thermal insulating layer306. The material of the second thermal insulating layer306is as same as the material of the first thermal insulating layer106. That is, the first thermal insulating layer106and the second thermal insulating layer306are disposed on the first surface102aof the positive electrode plate102and the second surface104aof the negative electrode plate104respectively. The thickness of the second thermal insulating layer306is about 0.1˜20 microns. In another embodiment (not shown), the first thermal insulating layer106is located at the second surface104aof the negative electrode plate104and the second thermal insulating layer306is located at the first surface102aof the positive electrode plate102. That is, for the charging-discharging surface of each of the positive electrode plate102and the negative electrode plate104, there is a layer of thermal insulating layer coated thereon.

FIG. 2is a schematic cross-sectional view showing a thermal insulating layer in a lithium battery according to one embodiment of the present application. As shown inFIG. 2, the thermal insulating layer400is comprised of, for example, an inorganic material402, a thermal activation material404and a binder406. The inorganic material402includes Al, Mg, Si, Zr, Ti, Zn, Li, Co or oxide thereof, hydroxide thereof, sulfide thereof, nitride thereof, halide thereof or the combination thereof. Preferably, the inorganic material includes silicon oxide (SiO2), aluminum oxide (Al2O3), zirconium oxide (ZrO2), magnesium oxide (MgO), titanium oxide (TiO2), lithium titanium oxide (LiTiO2) or zeolite. The binder406includes polyvinylidene fluoride (PVdF), styrene-butadiene rubber (SBR), polyamide, melamine resin or the combination thereof.

Moreover, the thermal activation material404includes a nitrogen-containing polymer. It should be noticed that the nitrogen-containing polymer includes the nitrogen-containing compound with the number average molecular weight at least 1500 or the nitrogen-containing oligomer with the number average molecular weight about 200˜2999. In one embodiment, the thermal activation material404includes the nitrogen-containing polymer which can be the hyper branched polymers formed by the reaction between diones and one selected from a group comprising amines, amides, imides, maleimides and imines. More specifically, the diones includes barbituric acid, derivatives of barbituric acid, acetylactone or derivatives of acetylactone. In another embodiment, the thermal activation material404includes the nitrogen-containing polymer which can be formed by, for example, the reaction between the bismaleimide and the barbituric acid.

The chemical structure of the aforementioned amine is shown as following:

Wherein, R1, R2and R3can be as same as or different from each other; each of R1, R2and R3can be hydrogen, aliphatic group or aromatic group. More specifically, the amine can be the primary amine in which R2and R3are both hydrogen. In one embodiment, the aforementioned amines include 1,1′-bis(methoxycarbonyl)divinylamine (BDA), N-methyl-N,N-divinylamine or divinylphenylamine.

The chemical structure of the aforementioned amide is shown as following:

Wherein, R, R′ and R″ can be as same as or different from each other; each of R, R′ and R″ can be hydrogen, aliphatic group or aromatic group. More specifically, the amide can be the primary amide in which R′ and R″ are both hydrogen. In one embodiment, the aforementioned amides include N-Vinylamide, divinylamide, Silyl(vinyl)amides or glyoxylated-vinyl amide.

The chemical structure of the aforementioned imide is shown as following:

Wherein, R1, R2and R3can be as same as or different from each other; each of R1, R2and R3can be hydrogen, aliphatic group or aromatic group. In one embodiment, the aforementioned imides include divinylimide such as N-Vinylimide, N-Vinylphthalimide and vinylacetamide.

The maleimides includes monomaleimide, bis-maleimide, tris-maleimide and polymaleimide. The monomer of the aforementioned bis-maleimide comprises chemical structure (I) and chemical structure (II) shown as followings:

The chemical structure of the aforementioned imine is shown as following:

Wherein, R1, R2and R3can be as same as or different from each other; each of R1, R2and R3can be hydrogen, aliphatic group or aromatic group. The aforementioned imines include divinylimine or allylic imine.

The chemical structures of the barbituric acid and derivatives of barbituric acid are shown as following:

The chemical structures of the acetylactone and derivatives of acetylactone are shown as following:

Wherein, each of R and R′ can be aliphatic group, aromatic group or heterocyclic group. Also, while both of R and R′ are methyl groups, the compound is acetylactone.

The mole ratio of the required amount of diones to the monomer of amines, amides, imides, maleimides or imines is about 1:20˜4:1. Preferably, the mole ratio is about 1:5˜2:1. More preferably, the mole ratio is about 1:3˜1:1.

It should be noticed that the thermal activation material404is micromolecule material which uniformly distributes in the binder406before the thermal activation. Therefore, the diffusion of the lithium ions in the lithium battery does not affected by the thermal activation material404. Once the temperature of the lithium battery increases, a cross-linking reaction of the thermal activation material404is initiated and the thermal activation material404is converted into the polymer so that the diffusion of the lithium ions is retarded and the conductivity of the electrolyte decreases. On other words, when the temperature of the lithium battery increases, the terminal groups of the thermal activation material404perform the cross-linking reaction to block the diffusion of the lithium ions. The temperature of the cross-linking reaction of the thermal activation material404is the onset temperature. For instance, when the nitrogen-containing polymer is formed by the reaction between bismaleimide and barbituric acid, the terminal groups of the thermal activation material404comprises ethenyl group (from bismaleimide) and amino group (from barbituric acid). When the temperature of the battery increases, the temperature of the cross-linking reaction of the ethenyl group with the amino group is the thermal activation temperature. In the present application, the thermal activation temperature is about 80˜280° C. Preferably, the thermal activation temperature is about 100˜220° C. More preferably, the thermal activation temperature is about 130˜200° C.

Table 1 shows the conductivities of the electrolytes before and after the thermal activation of the thermal activation material on the electrode plate initiates.

As shown in Table 1, the weight percentage of the thermal activation material in the thermal insulating layer is about 10 wt % and the thermal activation material is the nitrogen-containing polymer formed by the reaction between bismaleimide and barbituric acid. The ratio of ethenyl group (from bismaleimide) to amino group (from barbituric acid) is about 2 to 1. It should be noticed that, before the thermal activation of the thermal activation material initiates, the conductivity of the electrolyte of the lithium battery increases with the increasing of the temperature. However, after the thermal activation of the thermal activation material initiates, the conductivity of the electrolyte of the lithium battery decreases. Apparently, under the circumstance that a thermal insulating layer comprising the thermal activation material is disposed on the electrode plate of the lithium battery, the conductivity of the electrolyte can be effectively decreased after the thermal activation of the thermal activation material initiates.

As shown inFIG. 2, the inorganic material402and the thermal activation material404respectively in forms of a plurality of particles distribute in the binder406. The weight percentage of the thermal activation material404in the thermal insulating layer400is about 0.1˜40 wt %. Preferably, the weight percentage of the thermal activation material404in the thermal insulating layer400is about 1˜30 wt % or 2˜15 wt %. In the present embodiment, the particle of the inorganic material402is in round shape. However, the present application is not limited thereto. That is, the present application is not limited to that the inorganic material402is in a single particle form distributing in the binder406and that the shape of the particle of the inorganic material is round as shown inFIG. 2. On the other words, the particle of the inorganic material402can be in any shape, the inorganic material402distributing in the binder can be in single particle form or in cluster form which includes a plurality of particle of inorganic material. Similarly, as shown inFIG. 2, the particle of thermal activation material404is in polygon shape. However, the application is not limited thereto. That is, the application is not limited to that the thermal activation material404is in a single particle form distributing in the binder406and that the shape of the particle of the thermal activation material is polygon as shown inFIG. 2. On the other words, the particle of the thermal activation material404can be in any shape, the thermal activation material404distributing in the binder can be in single particle form or in cluster form which includes a plurality of particle of thermal activation material404.

FIG. 3is a schematic cross-sectional view showing a thermal insulating layer in a lithium battery according to another embodiment of the present application. As shown inFIG. 3, in another embodiment, the surface of each particle of the thermal activation material504in the thermal insulating layer500has a polymer thin film508coated thereon. That is, the polymer thin film508completely encloses each particle of the thermal activation material504distributing in the binder506. The material of the polymer thin film508includes polyolefine or polyethylene. In the present embodiment, when the temperature of the lithium battery increases, the polymer thin film508cracks due to the heat and the thermal activation material504enclosed by the polymer thin film508is released. Thus, the cross-linking reaction of the terminal groups of the released thermal activation material504initiates and the diffusion of the lithium ions is blocked.

Then, as shown inFIG. 1A, the separator108of the lithium battery100is located between the positive electrode plate102and the negative electrode plate104. It should be noticed that the positive electrode plate102, the negative electrode plate104, the thermal insulating layer106and the separator108are soaked in the electrolyte110. That is, the space between the positive electrode plate102, the negative electrode plate104, the thermal insulating layer106and the separator108are flooded with the electrolyte110. More specifically, the holes114of the separator108are flooded with the electrolyte110. The separator108includes insulating material such as polyethylene (PE), polypropylene (PP), Teflon film, polyamide film, polyvinyl chloride film, polyvinylidene fluoride film, polyaniline film, polyimide film, nonwoven fabric, polyethylene terephthalate, polystyrene (PS), cellulose or the multi-layered complex structure thereof such as PE/PP/PE. The main composition of the electrolyte110includes organic solvent, lithium salt and additive. The organic solvent can be, for example, γ-butyrolactone (GBL), ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), propyl acetate (PA), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC) or the combination thereof. The lithium salt can be, for example, LiPF6, LiBF4, LiAsF6, LiSbF6, LiClO4, LiAlCl4, LiGaCl4, LiNO3, LiC(SO2CF3)3, LiN(SO2CF3)2, LiSCN, LiO3SCF2CF3, LiC6F5SO3, LiO2CCF3, LiSO3F, LiB(C6H5)4, LiCF3SO3, LiB(C2O4)2or the combination thereof.

FIG. 4is a plot diagram showing the inner resistance varied with the change of the temperature. As shown inFIG. 4, the variation of the inner resistance with the change of the temperature is measured while the lithium battery is heated up. The dotted curve represents the variation of the inner resistance when an aluminum oxide layer is coated on the positive electrode plate of the lithium battery and the solid curve represents the variation of the inner resistance when an aluminum oxide layer containing 3% thermal activation material is coated on the positive electrode plate of the lithium battery. According to the curves shown inFIG. 4, the increasing amount of the inner resistance of the positive electrode plate having the thermal activation material coated thereon is larger than the increasing amount of the inner resistance of the positive electrode plate without any thermal activation material thereon. Apparently, the thermal activation material effectively blocks the diffusion of the lithium ions.

In the present application, the thermal insulating layer is disposed on one of or both of the positive electrode plate and the negative electrode plate. Since the thermal insulating layer comprises the inorganic material capable of increasing the hardness and the thermal activation material capable of initiating the thermal activation while the temperature of the lithium battery increases, the cross-linking reaction of the thermal activation material initiates and the thermal activation material is converted into the polymer. Thus, the diffusion of the lithium ions is blocked by the polymer and the conductivity of the electrolyte decreased.