Patent Description:
With the rapid development of consumer electronics and electric vehicles, the lithium-ion electronics industry has attracted widespread attention from all walks of life. The requirements for batteries are increasingly strict. As the core part of new energy vehicles, lithium-ion batteries are strictly required to have safety, reliability and stability.

A lithium-ion battery is composed of an electrode assembly and a metal case accommodating the electrode assembly. The case is usually an aluminum case. After the electrode assembly is assembled into the case, a cover plate is welded to the case by laser to realize the structural connection and sealing of the battery. Lithium-ion batteries need to be insulated during use to achieve the safety and reliability of battery module and battery pack. At present, the insulation requirements for lithium-ion batteries are generally implemented in the process of assembling batteries into a battery module or battery pack by sticking an insulating film to the surface. However, the insulating film is easily scratched or damaged by external substances, hard particles, etc. during production or operation, resulting in insulation failure to affect the safety performance of batteries.

<CIT> discloses an insulating powder coating and a battery case comprising the same. The battery case includes a housing, a cover, a first insulating barrier on the inside and a second insulating barrier on the outside surface of the housing.

<CIT> discloses a battery case made of aluminum or an aluminum alloy, and a protective coating layer applied to at least a portion of an outer surface of the battery case, the protective coating layer containing an electrically insulative polymer material.

<CIT> discloses an electrochemical energy storage device with a hard shell cell housing, a method for producing an electrochemical energy storage device with a hard shell cell housing.

Therefore, a new case, secondary battery, battery pack, vehicle, and method for manufacturing a secondary battery are urgently needed.

The present application provides a secondary battery, a battery pack, and a vehicle, aiming to improve the safety performance of the secondary battery.

The first aspect of the present application provides a secondary battery in accordance with claim <NUM>.

Optionally, the coated region has an area of from <NUM>% to <NUM>%, relative to a total area of the outer surface of the side wall; and/or, the coated region has an extension height of from <NUM>% to <NUM>% in the height direction, relative to a total height of the side wall.

Optionally, the non-coated region has an extension height of greater than or equal to <NUM> in the height direction.

The insulating coating includes: relative to a total weight of the insulating coating, <NUM>-<NUM> wt% of insulating film-forming resin, <NUM>-<NUM> wt% of auxiliary agent, and <NUM>-<NUM> wt% of pigment.

Optionally, the pigment is selected from a toner; and/or, the insulating film-forming resin is selected from epoxy resin, polyurethane, acrylic resin, phenolic resin, polyester resin, and combinations thereof; and/or, the auxiliary agent is selected from at least one of a light stabilizer, a heat stabilizer, an antioxidant, a defoamer, a leveling agent, a flame retardant, and a plasticizer.

Optionally, the insulating film-forming resin is obtained by photo-curing an acrylic functionalized prepolymer and an acrylic monomer in the presence of a photoinitiator, wherein the acrylic functionalized prepolymer is selected from at least one of a polyester acrylate prepolymer, epoxy acrylate prepolymer, urethane acrylate prepolymer and pure acrylate prepolymer, and the acrylic monomer is selected from at least one of monoalkyl acrylate, diol diacrylate and triol triacrylate; or, the insulating film-forming resin is obtained by curing reaction of epoxy resin, polyurethane, polyester or acrylic resin with a curing agent.

Optionally, the insulating coating has a thickness of from <NUM> to <NUM>.

Optionally, the bonding segment is bonded to the non-coated region, and the stacking segment extends from the bonding segment to an outer surface of the insulating coating.

The stacking segment has an extension height of from <NUM> to <NUM> in the height direction.

The second aspect of the present application provides a battery pack, including: a box; and the above-mentioned secondary batteries, the secondary batteries being accommodated in the box.

Optionally, the secondary batteries are adhered to an inner wall surface of the box by an adhesive.

The third aspect of the present application provides a vehicle, including the above-mentioned battery pack.

In the secondary battery according to the present application, the case includes a bottom wall, a side wall, and a coated region and a non-coated region on an outer surface of the side wall, and the coated region is coated with an insulating coating. The bottom wall and the side wall enclose an accommodating cavity with an opening, and an electrode assembly of a secondary battery can be placed into the accommodating cavity from the opening. The coated region extends, in a height direction, from the side of the side wall that is close to the bottom wall to a position near the side of the side wall that is close to the opening, so as to reserve the non-coated region on the outer surface near the edge of the opening. As such, when a cover plate of the secondary battery is welded to the case at the opening, the high temperature caused by welding will not affect the stability of the insulating coating on the coated region. The outer surface of the side wall is coated with the insulating coating, and the adhesive force between the insulating coating and the side wall is relatively large, which can ensure the flatness and good insulation performance of the outer surface of the side wall. Therefore, during the production and use of the case, the insulating coating can be well bonded to the coated region for a long term, achieving better long-term safety and reliability of the case.

The features, advantages, and technical effects of exemplary embodiments of the present application will be described below with reference to the accompanying drawings, and the accompanying drawings are not drawn according to actual scale.

<NUM>, case; <NUM>, bottom wall; <NUM>, side wall; <NUM>, insulating coating; <NUM>, second insulating film; <NUM>, bonding segment; <NUM>, stacking segment; <NUM>, opening; <NUM>, accommodating cavity; <NUM>, cover plate; <NUM>, first insulating film; <NUM>, electrode terminal; Z, height direction.

The features and exemplary embodiments of various aspects of the present application will be described in detail below. In the following detailed description, many specific details are given in order to provide a comprehensive understanding of the present application. However, it will be obvious to those skilled in the art that the present application may be implemented without some of these specific details. The following description of the embodiments is only to provide a better understanding of the present application by showing examples of the present application. In the drawings and the following description, at least part of the well-known structures and technologies are not shown in order to avoid unnecessary blurring of the present application; and, for clarity, the sizes of some structures may be exaggerated. Furthermore, the features, structures or characteristics described hereinafter may be combined in any suitable manner in one or more embodiments.

In the description of the present application, it should be noted that, unless otherwise specified, "plurality of" means two or more; the orientations or positional relationships indicated by the terms "upper", "lower", "left", "right", "inner", "outer", etc. are only for facilitating description of the present application and simplifying the description, but do not indicate or imply that the pointed apparatuses or elements must have specific orientations or be constructed and operated in specific orientations. Therefore, the terms should not be understood to limit the present application.

The orientation terms appearing in the following description all indicate directions shown in the drawings, and are not intended to limit the specific structures of the embodiments of the present application. In the description of the present application, it should also be noted that, unless otherwise clearly specified and defined, the terms "mounted" and "connected" should be understood broadly; for example, the term "connected" may refer to two components that are fixedly connected, detachably connected, integrally connected, directly connected, or indirectly connected. Those of ordinary skill in the art could understand the specific meanings of the above terms in the present application depending on specific circumstances.

In order to better understand the present application, the case, secondary battery, battery pack, vehicle, and method for manufacturing a secondary battery according to the embodiments of the present application will be described in detail below in conjunction with <FIG>.

The present application first provides a vehicle, which is provided with a battery pack. The battery pack includes a box and a secondary battery accommodated in the box.

<FIG> is a schematic structural diagram of a secondary battery according to an embodiment of the application. The secondary battery includes: a case <NUM> including a bottom wall <NUM> and a side wall <NUM>, the bottom wall <NUM> and the side wall <NUM> defining an accommodating cavity <NUM> with an opening <NUM> at one end; an electrode assembly (not shown in the figure) located in the accommodating cavity <NUM>, the electrode assembly being formed by winding a positive electrode plate, a negative electrode plate and a separator, or by stacking a positive electrode plate, a negative electrode plate and a separator, the accommodating cavity <NUM> being filled with an electrolyte; and a cover plate <NUM> covering the opening <NUM> in a sealing manner.

The case <NUM> and the cover plate <NUM> may be connected in various ways. Optionally, the case <NUM> and the cover plate <NUM> are connected to each other by welding to ensure the stability of a relative position and the reliability of connection and sealing between the case <NUM> and the cover plate <NUM>.

In some optional embodiments, the case <NUM> of the secondary battery is made of a metal material, such as aluminum or steel. In order to prevent electrochemical corrosion of the metal case <NUM>, the metal case <NUM> is positively charged under normal circumstances. When the secondary battery is assembled into a battery module or a battery pack, metal particles may fall onto the secondary battery to electrically connect the case <NUM> of the secondary battery with a negative electrode, causing an external short circuit of the secondary battery to affect the safety performance of the secondary battery. Therefore, insulation protection is required for the secondary battery.

An outer surface of the cover plate <NUM> away from the accommodating cavity <NUM> is provided with a first insulating film <NUM>. The arrangement of the first insulating film <NUM> is not limited. For example, the cover plate <NUM> is further provided with protruding structures such as electrode terminals <NUM>. The electrode terminals <NUM> may include a positive electrode terminal and a negative electrode terminal. The first insulating film <NUM> is provided with through holes from which the electrode terminals <NUM> extend out. Gaps are prevented between the first insulating film <NUM> and the cover plate <NUM> due to the protruding structures, the contact area between the cover plate <NUM> and the first insulating film <NUM> is increased, and the stability of a relative position and the reliability of connection between the cover plate <NUM> and the first insulating film <NUM> are thus improved.

The first insulating film <NUM> may be configured in various ways. For example, the first insulating film <NUM> includes one or more of polyethylene terephthalate, polyimide, polycarbonate, polyethylene, polyvinylidene fluoride, and polytetrafluoroethylene.

In order to ensure the insulation performance of the case <NUM> of the secondary battery, the case <NUM> may be configured in various ways. For example, the case <NUM> may be covered with an insulating film.

In other optional embodiments, an outer surface of the side wall <NUM> includes a coated region coated with an insulating coating <NUM>, and the coated region extends, in a height direction (Z direction in <FIG>) of the side wall <NUM>, from the side of the side wall <NUM> that is close to the bottom wall <NUM> to a position near an edge of the side of the side wall <NUM> that is close to the opening <NUM>, so as to reserve a non-coated region with a preset height on the outer surface of the side wall <NUM> that is near the edge of the opening <NUM>. The coated region does not extend to the edge of the opening <NUM> in the height direction, the insulating coating <NUM> does not completely cover the outer surface of the side wall <NUM>, and the coated region is close to the edge of the opening <NUM> in the height direction but separated from the edge of the opening <NUM> by a predetermined distance, defining the non-coated region on the outer surface of the side wall <NUM>, which is not covered by the insulating coating <NUM>. That is, the outer surface of the side wall <NUM> includes a coated region and a non-coated region successively arranged in the height direction, the coated region is closer to the bottom wall <NUM> than the non-coated region, and the non-coated region is closer to the opening <NUM> than the coated region. The outer surface of the side wall <NUM> refers to the surface of the side wall <NUM> away from the accommodating cavity <NUM>. In some optional embodiments, the side of the side wall <NUM> that is close to the bottom wall <NUM> is specifically a junction between the side wall <NUM> and the bottom wall <NUM>.

The insulating coating <NUM> may be configured in various ways, and the insulating coating <NUM> is usually formed by applying an organic coating to the coated region. The coating is sensitive to temperature. If the ambient temperature of the insulating coating <NUM> is too high and higher than the melting point of the coating, the insulating coating <NUM> is likely to melt, which will affect the stability and insulation protection performance of the insulating coating <NUM>.

In the case <NUM> of the embodiment of the present application, the coated region extends, in the height direction, from the side of the side wall <NUM> that is close to the bottom wall <NUM> to a position near the side of the side wall <NUM> that is close to the opening <NUM>, so as to reserve the non-coated region on the outer surface of the side wall <NUM> that is near the edge of the opening <NUM>. As such, when the cover plate <NUM> of the secondary battery is welded to the case <NUM> at the opening <NUM>, the high temperature caused by welding will not affect the stability of the insulating coating <NUM> on the coated region. The outer surface of the side wall <NUM> is coated with an insulating coating <NUM>, the adhesion of the insulating coating <NUM> is relatively strong, and the adhesive force between the insulating coating <NUM> and the side wall <NUM> is relatively large, which can ensure the flatness of the outer surface of the side wall <NUM> and good insulation performance. Therefore, during the production and use of the case <NUM>, the insulating coating <NUM> can be well bonded to the coated region for a long term, achieving a better long-term safety and reliability of the case <NUM>.

Further, in other optional embodiments, the outer surface of the bottom wall <NUM> away from the accommodating cavity <NUM> is also coated with the insulating coating <NUM>. As such, when the secondary battery is disposed in the box of the battery pack, the insulation performance between the bottom wall <NUM> of the secondary battery and a bottom plate of the box can be ensured. Further, the insulating coating <NUM> coated on the outer surface of the side wall <NUM> and the insulating coating <NUM> coated on the outer surface of the bottom wall <NUM> are configured integrally.

When the outer surface of the case <NUM> of the secondary battery is coated with the insulating coating <NUM>, the secondary battery is adhered to an inner wall surface of the box by an adhesive. Since the outer surface of the case <NUM> is provided with the insulating coating <NUM>, the relative position between the insulating coating <NUM> and the bottom wall <NUM> or the side wall <NUM> is more stable. When the secondary battery is adhered to the inner wall surface of the box, the stability of the relative position between the secondary battery and the case will not be affected due to the relative movement of the insulating coating <NUM> with respect to the case <NUM>.

The inner wall surface of the box is not limited. In some optional embodiments, the box includes a bottom plate, a plurality of side plates connected to a peripheral side of the bottom plate, an accommodating space enclosed by the bottom plate and the plurality of side plates, a box opening communicated with the accommodating space, and an upper cover covering the box opening, the upper cover and the bottom plate being disposed oppositely in the height direction of the box. The inner wall surface of the box may be the surface of the bottom plate facing the accommodating space, or the surface of the side plates or the upper cover facing the accommodating space.

Optionally, the inner wall surface of the box is the surface of the bottom plate facing the accommodating space, and the secondary battery is adhered to the bottom plate by an adhesive, so that the secondary battery is fixed to the bottom plate of the box.

The area and shape of the coated region are not limited here. In order to ensure good insulation performance on the outer surface of the case <NUM> and good adhesion between the insulating coating <NUM> and the case <NUM>, the coated region has an area of from <NUM>% to <NUM>%, relative to a total area of the outer surface of the side wall <NUM>. Further, the coated region has an area of <NUM>%, relative to a total area of the outer surface of the side wall <NUM>.

The case <NUM> is usually prismatic or cylindrical. In order to ensure good adhesion between the insulating coating <NUM> and the case <NUM>, an extension height h of the coated region in the height direction and a total height H of the side wall <NUM> should satisfy the following relation: <MAT>.

That is, the coated region has an extension height of from <NUM>% to <NUM>% in the height direction, relative to a total height of the side wall <NUM>. It can also ensure that the insulating coating <NUM> occupies a large area on the outer surface of the side wall <NUM>, and ensure good adhesion performance between the insulating coating <NUM> and the side wall <NUM>.

In other optional embodiments, in order to ensure that the insulating coating <NUM> is not affected during the welding of the cover plate <NUM> and the case <NUM>, the extension height m of the non-coated region in the height direction is greater than or equal to <NUM>. When the cover plate <NUM> is welded to the opening <NUM> of the case <NUM>, the high temperature region caused by welding is limited. The height m of the non-coated region near the opening <NUM> is greater than or equal to <NUM>, which can effectively ensure that the high temperature produced during the welding will not be spread to the coated region to affect the stability of the insulating coating <NUM>.

In some optional embodiments, the edge of the coated region that is close to the opening <NUM> and the edge of the side wall <NUM> that is close to the opening <NUM> are disposed in parallel. As such, the non-coated region has the same height at different positions in the circumferential direction of the case <NUM>, and the stability of the insulating coating <NUM> will not be affected on the circumferential side of the opening <NUM> during the welding of the cover plate <NUM> and the case <NUM>.

In order to ensure good insulation performance, the insulating coating <NUM> needs to have a certain thickness. In some optional embodiments, the insulating coating <NUM> has a thickness of from <NUM> to <NUM>. Further, the insulating coating <NUM> has a thickness of from <NUM> to <NUM>. When the thickness of the insulating coating <NUM> is within said thickness range, it can not only ensure that the insulation performance of the insulating coating <NUM> meets the requirements, but also can prevent too large size of the case <NUM> due to excessive thickness of the insulating coating <NUM>. The excessive thickness of the insulating coating <NUM> will also lead to waste of the coating for the insulating coating <NUM> and reduce the energy density of the secondary battery.

The thickness of the insulating coating <NUM> refers to a distance between the outer surface of the insulating coating <NUM> away from the accommodating cavity <NUM> and the outer surface of the side wall <NUM>. There may be a certain variation in the thickness of the insulating coating <NUM> everywhere in the coated region. The thickness of the insulating coating <NUM> may be an average thickness of the insulating coating <NUM> everywhere in the coated region, or the thickness of the insulating coating <NUM> may be a minimum thickness of the insulating coating <NUM> everywhere in the coated region.

As described above, in order to improve the adhesion of the insulating coating <NUM>, the insulating coating <NUM> is formed by applying an organic coating to the coated region. The insulating coating <NUM> includes: relative to a total weight of the insulating coating, <NUM>-<NUM> wt% of insulating film-forming resin, <NUM>-<NUM> wt% of auxiliary agent, and <NUM>-<NUM> wt% of pigment.

Optionally, the insulating coating <NUM> includes <NUM>-<NUM> wt% of pigment. The pigment may be selected to have a designated color, such as blue, yellow, or red color. The pigment is added to the insulating coating <NUM>. When the insulating coating <NUM> is coated on the outer surface of the side wall <NUM>, it is easy to distinguish one from another, so that the user can determine the coated area of the insulating coating <NUM> according to the color of the insulating coating <NUM>.

In some optional embodiments, the pigment is selected from toners. For example, the toners include blue powder and titanium dioxide. The blue powder may be, for example, phthalocyanine blue powder. The ratio of the blue powder to the titanium dioxide is not limited here. For example, the ratio of the blue powder to the titanium dioxide is <NUM>: <NUM>.

In other optional embodiments, pigment powders in the pigment have a particle size of less than or equal to <NUM>. This can prevent the too large particle size of the pigment powders from affecting the performance of the insulating coating <NUM>.

The insulating film-forming resin may be configured in various ways. For example, the insulating film-forming resin is selected from epoxy resin, polyurethane resin, acrylic resin, phenolic resin, polyester resin, and combinations thereof. It can not only ensure that the insulating coating <NUM> has good insulation performance, but also can ensure that the insulating coating <NUM> has good adhesion, resistivity, etc..

The auxiliary agent may be configured in various ways. For example, the auxiliary agent is selected from at least one of a light stabilizer, a heat stabilizer, an antioxidant, a defoamer, a leveling agent, a flame retardant, and a plasticizer. This is beneficial to the curing and molding of the insulating coating <NUM> later.

The insulating coating <NUM> may be photo-cured or thermo-cured. For example, the insulating film-forming resin is obtained by photo-curing an acrylic functionalized prepolymer and an acrylic monomer in the presence of a photoinitiator, wherein the acrylic functionalized prepolymer is selected from at least one of a polyester acrylate prepolymer, epoxy acrylate prepolymer, urethane acrylate prepolymer and pure acrylate prepolymer, and the acrylic monomer is selected from at least one of monoalkyl acrylate, diol diacrylate and triol triacrylate.

Alternatively, in other optional embodiments, the insulating film-forming resin is obtained by curing reaction of epoxy resin, polyurethane, polyester or acrylic resin with a curing agent.

As an embodiment of the present application, when the insulating coating <NUM> is formed by photo-curing, the insulating coating <NUM> includes, for example, <NUM>-<NUM> wt% of pigment, <NUM>-<NUM> wt% of prepolymer, <NUM>-<NUM> wt% of monomer, <NUM>-<NUM> wt% of photoinitiator, and <NUM>-<NUM> wt% of auxiliary agent.

The prepolymer includes, for example, a polyester acrylate prepolymer, which has fast curing speed, high gloss and good adhesion; or the prepolymer includes an epoxy acrylate prepolymer, which has good chemical resistance, heat resistance, fullness and adhesion; or, the prepolymer includes a urethane acrylate prepolymer, which has the advantages of low energy, low shrinkage, good leveling, and improved toughness; or the prepolymer includes a pure acrylate prepolymer, which has the advantages of low viscosity and good leveling appearance.

The monomer is an organic small molecule including a polymerizable functional group, is easy to dissolve and dilute, and can adjust the viscosity of the system. The monomer includes, for example, alkyl acrylate, which has the characteristics of low viscosity, strong diluting ability, low photo-curing speed, low cross-linking density, low volume shrinkage, etc. Alternatively, the monomer includes dipropylene glycol diacrylate, which can effectively improve the adhesion of the insulating coating. Alternatively, the monomer includes trihydroxymethylpropane triacrylate, which has the characteristics of fast photo-curing speed, high cross-linking density, high film hardness and brittleness, good resistance, large molecular weight, high viscosity, etc..

After the photoinitiator absorbs light energy, it can jump to an excited singlet state, and then jump to an excited triplet state through intersystem crossing, and its molecular structure is unstable in the excited singlet or triplet state. The weak bond in the photoinitiator undergoes homolysis to generate active free radicals, which initiate the polymerization and cross-linking of oligomers and monomers. An absorption spectrum of the photoinitiator matches an emission spectrum of a light source. The photoinitiator may be, for example, an ITX photoinitiator or TPO photoinitiator suitable for colored systems. Alternatively, the photoinitiator is a <NUM> photoinitiator or <NUM> photoinitiator which can be dried quickly.

The auxiliary agent may be, for example, a chain transfer agent, a light or heat stabilizer, a plasticizer, an oxygen inhibitor, or a free radical trapping agent.

As another embodiment of the present application, when the insulating coating <NUM> is formed by thermo-curing, the insulating coating <NUM> includes, for example, <NUM>-<NUM> wt% of pigment, <NUM>-<NUM> wt% of matrix resin, <NUM>-<NUM> wt% of curing agent, and <NUM>-<NUM> wt% of auxiliary agent.

The matrix resin may include, for example, epoxy resin, which has the characteristics of strong adhesion, strong mechanical properties, low curing shrinkage, good chemical stability, etc..

The curing agent may include, for example, phenolic resin, which has the characteristics of good wear resistance, high strength, good corrosion resistance, etc. The curing agent may also include dicyandiamide and the like.

The auxiliary agent may include, for example, a defoamer, a leveling agent, a flame retardant, a plasticizer, etc..

In order to ensure the overall insulation of the case <NUM>, in some optional embodiments, the secondary battery further includes a second insulating film <NUM>, which covers at least the non-coated region to ensure insulation of the non-coated region.

Referring to <FIG> together, the second insulating film <NUM> may be configured in various ways. For example, the second insulating film <NUM> covers only the non-coated region. In other optional embodiments, the bonding segment <NUM> is bonded to the non-coated region, and the stacking segment <NUM> extends from the bonding segment <NUM> to the outer surface of the insulating coating <NUM>. In these optional embodiments, the second insulating film <NUM> and the insulating coating <NUM> can be stacked on each other through the stacking segment <NUM>, which prevents a gap between the second insulating film <NUM> and the insulating coating <NUM> affecting the insulation performance of the outer surface of the case <NUM>.

The stacking height of the second insulating film <NUM> and the insulating coating <NUM> is not limited, that is, the extension height of the stacking segment <NUM> in the height direction is not limited. The stacking segment <NUM> has an extension height of from <NUM> to <NUM> in the height direction. Further, optionally, the stacking segment <NUM> has an extension height of from <NUM> to <NUM> in the height direction. When the extension height of the stacking segment <NUM> is within the above range, it can prevent a gap between the second insulating film <NUM> and the insulating coating <NUM> affecting the insulation performance of the outer surface of the case <NUM>, and can also prevent waste of materials due to excessive extension height of the stacking segment <NUM>.

In some optional embodiments, the second insulating film <NUM> has a thickness of from <NUM> to <NUM>. Optionally, the second insulating film <NUM> has a thickness of <NUM>. When the thickness of the second insulating film <NUM> is within the above numerical range, it can prevent the increase in the size of the secondary battery due to the too thick second insulating film <NUM>, and can also ensure certain wear resistance of the second insulating film <NUM>, prolong the service life of the second insulating film <NUM> and improve the insulation performance of the case <NUM>.

The second insulating film <NUM> and the first insulating film <NUM> are disposed integrally, which can improve the assembly efficiency of the secondary battery.

In some optional embodiments, the material of the second insulating film <NUM> is the same as that of the first insulating film <NUM>, so details are not described herein again.

Referring to <FIG>, the fourth aspect of the present application further provides a method for manufacturing a secondary battery, including:
Step S001: providing a case.

The case may be the case in any of the above embodiments.

Step S002: placing an electrode assembly into the accommodating cavity from the opening.

Step S003: covering the opening by a cover plate, and welding the cover plate and the side wall to each other.

Step S004: bonding an insulating film to the outside of the side wall, the insulating film covering at least the non-coated region.

In the method of the embodiment of the present application, before step S002 and step S003, that is, before the cover plate <NUM> and the case <NUM> are welded, the electrode assembly is placed and the cover plate <NUM> is closed, the insulating coating <NUM> is coated because the case at this time is relatively light and simple in structure, facilitating the application of the insulating coating <NUM>. In step S003, the non-coated region can prevent the high temperature caused by welding from affecting the stability of the insulating coating <NUM>. Through step S004, the insulation performance of the outer surface of the side wall <NUM> can be further improved, and safety accidents caused by electrification of the non-coated region can be prevented.

In some optional embodiments, step S001 includes:
Step S011: providing a case body.

<FIG> shows a case body according to an embodiment of the present application. The case body includes a side wall <NUM>, a bottom wall <NUM>, an accommodating cavity <NUM>, and an opening <NUM>.

The cleaning method includes but is not limited to: ethanol cleaning, acetone cleaning, butanone cleaning, isoacetone cleaning, laser cleaning, plasma cleaning, etc. After cleaning, the case body has a surface energy of greater than <NUM> N/m.

As shown in <FIG>, after the case body is cleaned, the outer surface of the side wall <NUM> of the case body is divided into a coated region and a non-coated region. In order to highlight the coated region and the non-coated region, the boundary between the coated region and the non-coated region is shown by a dotted line in <FIG>. It can be understood that the dotted line does not constitute a limitation on the structure of the case body. In <FIG>, the portion with an extension size m in the height direction is the non-coated region, the portion with an extension size h in the height direction is the coated region, and the non-coated region is located on the side of the coated region that is close to the opening <NUM>.

Step S013: coating the coated region with the insulating coating <NUM> to form the case as described in any of the above embodiments.

As shown in <FIG>, the coated region of the side wall <NUM> is coated with the insulating coating <NUM>.

Then, the electrode assembly is placed in the case according to step S002. Next, as shown in <FIG>, the opening <NUM> is covered by the cover plate <NUM> in step S003. Finally, the cover plate <NUM> and the side wall <NUM> are welded to each other in the non-coated region, the second insulating film <NUM> is bonded to the non-coated region of the side wall <NUM> so that the second insulating film <NUM> covers at least part of the insulating coating <NUM>, and the first insulating film <NUM> is bonded to the top of the cover plate <NUM> to form the secondary battery described in any of the above embodiments.

The coated region is coated with the insulating coating by, but not limited to, an adhesive.

Claim 1:
A secondary battery, comprising:
a case (<NUM>) for a secondary battery, the case (<NUM>) comprising a bottom wall (<NUM>) and a side wall (<NUM>), the bottom wall (<NUM>) and the side wall (<NUM>) defining an accommodating cavity (<NUM>) with an opening (<NUM>) at one end for accommodating an electrode assembly of the secondary battery;
an electrode assembly placed in the accommodating cavity (<NUM>);
a cover plate (<NUM>) covering the opening (<NUM>); and
a second insulating film (<NUM>) covering at least the non-coated region,
wherein, an outer surface of the side wall (<NUM>) comprises a coated region coated with an insulating coating (<NUM>), and the coated region extends, in a height direction of the side wall (<NUM>), from a side of the side wall (<NUM>) that is close to the bottom wall (<NUM>) to a position near an edge of a side of the side wall (<NUM>) that is close to the opening (<NUM>), so as to reserve a non-coated region with a preset height on the outer surface of the side wall (<NUM>) that is near an edge of the opening (<NUM>), and
the insulating coating (<NUM>) comprises: relative to a total weight of the insulating coating (<NUM>), <NUM>-<NUM> wt% of insulating film-forming resin, <NUM>-<NUM> wt% of auxiliary agent, and <NUM>-<NUM> wt% of pigment, and
the second insulating film (<NUM>) comprises a bonding segment (<NUM>) and a stacking segment (<NUM>) successively arranged in the height direction, and the stacking segment <NUM> has an extension height of from <NUM> to <NUM> in the height direction, and
wherein an outer surface of the cover plate (<NUM>) away from the accommodating cavity (<NUM>) is provided with a first insulating film (<NUM>), and the second insulating film (<NUM>) and the first insulating film (<NUM>) are disposed integrally.