Negative electrode sheet and preparation method and application thereof

Abstract

The present invention relates to a negative electrode plate and a preparation method and application thereof, wherein the negative electrode plate comprises a negative electrode current collector, and a negative electrode active material layer and a protective layer stacked on the surface of the negative electrode current collector; wherein the protective layer comprises a thermal expansion polymer substrate, and a metal peroxide distributed in the thermal expansion polymer substrate. The negative electrode plate of the present invention can effectively inhibit the formation of lithium dendrites, isolate the contact between positive and negative electrodes, fundamentally solve the internal short circuit problem, and thus realize efficient and safe protection of batteries and electrical equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a negative electrode sheet and a preparation method and application thereof. Background Art

[0002] Traditional lithium-ion batteries have certain safety failure risks during use, for example: (1) Although fast-charging lithium batteries can be charged at high currents to shorten charging time, when the charging current is increased, due to various factors such as temperature, voltage, and current control, increased polarization, etc., lithium ions are not inserted into graphite, but are directly reduced to lithium metal on the surface of the negative electrode, gradually developing into lithium dendrites. As the lithium dendrites grow, they may penetrate the diaphragm and directly contact the positive electrode, thereby causing a short circuit between the positive and negative electrodes and affecting the safety performance of the battery; (2) When due to certain factors When the positive and negative electrodes inside the battery cell are in direct contact and cause a short circuit, a large amount of heat will be released at the short-circuit site, causing the temperature inside the battery cell to rise rapidly. When it reaches a certain temperature threshold, the volume of the diaphragm in the battery will shrink due to thermal shock, making the diaphragm that originally separates the positive and negative electrodes lose its function, thereby causing a larger area of ​​positive and negative electrodes to be short-circuited, continuing to release heat, and the temperature continues to rise. The electrolyte, SEI membrane and other components in the battery decompose at high temperature and produce a large amount of gas, causing the gas pressure in the battery cell to rise rapidly, worsening thermal runaway, and ultimately leading to uncontrolled explosion and fire of the battery cell.

[0003] Although a ceramic powder coating is provided on the surface of the diaphragm, the thermal shrinkage of the diaphragm can be improved to a certain extent, thereby delaying the occurrence of thermal shrinkage and prolonging the time before thermal runaway occurs, the internal short circuit problem still exists, and the risk of thermal runaway caused by internal short circuit cannot be fundamentally avoided. Summary of the invention

[0004] Based on this, it is necessary to provide a negative electrode plate and its preparation method and application to address the above problems; the negative electrode plate can effectively inhibit the formation of lithium dendrites and isolate the contact between the positive and negative electrodes, fundamentally solving the internal short circuit problem, thereby achieving efficient and safe protection of batteries and electrical equipment.

[0005] A negative electrode sheet comprises a negative electrode current collector, and a negative electrode active material layer and a protective layer stacked on the surface of the negative electrode current collector;

[0006] Wherein, the protective layer comprises a heat-expandable high molecular polymer substrate and a metal peroxide distributed in the heat-expandable high molecular polymer substrate.

[0007] In one embodiment, the thickness of the protective layer is 5%-15% of the thickness of the negative electrode active material layer.

[0008] In one embodiment, the thickness of the protective layer is 10 μm-20 μm;

[0009] And / or, the thickness of the negative electrode active material layer is 125 μm-150 μm.

[0010] In one embodiment, the mass fraction of the metal peroxide in the protective layer is 15%-30%;

[0011] And / or, in the composite layer composed of the negative electrode active material layer and the protective layer, the density of the metal peroxide is 15.5 mg / cm 3 -18.5mg / cm 3 .

[0012] In one embodiment, the metal peroxide includes at least one of sodium peroxide and potassium peroxide.

[0013] In one embodiment, the thermal expansion coefficient of the thermally expandable polymer substrate is 40ppm / °C-80ppm / °C;

[0014] And / or, the material of the heat-expandable polymer substrate includes at least one of epoxy resin, polyacrylate, polyimide, polyvinyl acetate, ethylene-propylene rubber, acrylonitrile-butadiene-styrene copolymer, ethylene-vinyl acetate copolymer, and ethylene-ethyl acrylate copolymer.

[0015] In one of the embodiments, the mass ratio of the metal peroxide to the negative electrode active material in the negative electrode active material layer is 1:140-1:160.

[0016] A method for preparing the negative electrode sheet as described above comprises the following steps:

[0017] Prepare negative electrode slurry and place it on the surface of negative electrode current collector to form a negative electrode slurry layer;

[0018] The heat-expandable high molecular polymer powder, metal peroxide powder and conductive glue are mixed and placed on the surface of the negative electrode slurry layer, and the negative electrode plate is obtained after drying and pressing.

[0019] A battery comprises the negative electrode sheet as described above, wherein the protective layer in the negative electrode sheet faces the positive electrode sheet.

[0020] An electrical device comprises the battery as described above.

[0021] The negative electrode plate described in the present invention, by providing a protective layer on the surface of the negative electrode active material layer, utilizes the synergistic effect of the heat-expandable high molecular polymer and the metal peroxide in the protective layer, on the one hand, oxidizes the lithium metal on the surface of the negative electrode to avoid the lithium metal from forming lithium dendrites, thereby achieving intrinsic safety protection, and can also oxidize the strong reducing gas in the early stage of SEI film decomposition, which is beneficial to further enhance the intrinsic safety of the electrode structure; on the other hand, not only the high temperature resistance is improved, but also the volume expansion can be generated at high temperature, effectively avoiding direct contact between the positive and negative electrodes, even if the separator in the battery is heated and the volume shrinks, it will not cause the positive and negative electrodes short circuit problem, at the same time, during the expansion process, air pressure and capillary action are generated inside the heat-expandable high molecular polymer, and free electrolyte can be adsorbed into the expanded heat-expandable high molecular polymer, thereby avoiding electrolyte combustion, reducing the risk of thermal runaway, and improving battery safety.

[0022] Therefore, the negative electrode plate provided by the present invention can effectively inhibit the formation of lithium dendrites and isolate the contact between the positive and negative electrodes, fundamentally solving the internal short circuit problem, thereby achieving efficient and safe protection of batteries and electrical equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 Schematic diagram of the structure of the negative electrode plate in one embodiment of the present invention.

[0025] Reference numerals: 10, negative electrode current collector; 20, negative electrode active material layer; 30, protective layer; 301, thermally expandable high molecular polymer substrate; 302, metal peroxide. DETAILED DESCRIPTION

[0026] For ease of understanding of the present invention, the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific implementation methods or embodiments, and are not intended to limit the present invention. The optional scope of the term "and / or" used herein includes any one of two or more related listed items, and also includes any and all combinations of related listed items, and the combinations include any two related listed items, any more related listed items, or all related listed items.

[0028] Combination Figure 1 As shown, a negative electrode sheet provided by the present invention includes a negative electrode current collector 10 , and a negative electrode active material layer 20 and a protective layer 30 stacked on the surface of the negative electrode current collector 10 .

[0029] The protective layer 30 includes a thermally expandable polymer matrix 301 and a metal peroxide 302 distributed in the thermally expandable polymer matrix 301 .

[0030] The protective layer 30 in the negative electrode plate of the present invention can oxidize the lithium metal precipitated on the surface of the negative electrode due to rapid charging during high-current rapid charging, thereby preventing the lithium metal from forming lithium dendrites, thereby achieving intrinsic safety protection, and can also oxidize the strong reducing gas in the early stage of SEI film decomposition, which is beneficial to further enhance the intrinsic safety of the electrode structure.

[0031] At the same time, the protective layer 30 not only has excellent high temperature resistance, but also can produce volume expansion at high temperature, effectively avoiding direct contact between the positive and negative electrodes. Even if the diaphragm in the battery shrinks in volume due to heat and fails, the thermally expandable polymer substrate 301 can also replace the diaphragm to achieve the effect of blocking the positive and negative electrodes, thereby fundamentally solving the internal short circuit problem.

[0032] In addition, the air pressure and capillary action generated inside the thermally expandable polymer during the expansion process can also adsorb the free electrolyte into the expanded thermally expandable polymer, thereby avoiding electrolyte combustion, reducing the risk of thermal runaway, and improving battery safety.

[0033] By adjusting the thickness of the protective layer 30 and the negative electrode active material layer 20 , the influence of the protective layer 30 on the negative electrode electrical performance is further reduced while ensuring that the protective layer 30 can effectively oxidize lithium metal and prevent expansion.

[0034] Preferably, the thickness of the protective layer 30 is 5%-15% of the thickness of the negative electrode active material layer 20, specifically, including but not limited to any point value among 5%, 6%, 7%, 8%, 9%, 10%, 12.5%, 15% or any range value between two thereof.

[0035] More preferably, the protective layer 30 has a thickness of 10 μm-20 μm, specifically, including but not limited to any value among 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm or any range between two values.

[0036] More preferably, the thickness of the negative electrode active material layer 20 is 125 μm-150 μm, specifically, including but not limited to any value among 125 μm, 130 μm, 135 μm, 140 μm, 145 μm, 150 μm or any range between two values.

[0037] By regulating the content of the metal peroxide 302 in the protective layer 30 , it is beneficial to further enhance the intrinsic safety of the electrode structure.

[0038] Preferably, the mass fraction of the metal peroxide 302 in the protective layer 30 is 15%-30%, specifically, including but not limited to any point value among 15%, 20%, 25%, 30% or any range value between the two.

[0039] More preferably, in the composite layer composed of the negative electrode active material layer 20 and the protective layer 30, the density of the metal peroxide 302 is 15.5 mg / cm 3 -18.5mg / cm 3 , specifically, including but not limited to 15.5 mg / cm 3 、16.0mg / cm 3 、16.5mg / cm 3 、17.0mg / cm 3 、17.5mg / cm 3 、18.0mg / cm 3 、18.5mg / cm 3 Any point value in or any range of values ​​between them.

[0040] In one embodiment, the metal peroxide 302 includes but is not limited to at least one of sodium peroxide, potassium peroxide, and calcium peroxide, preferably sodium peroxide or potassium peroxide.

[0041] Preferably, the thermal expansion coefficient of the thermally expandable polymer substrate 301 is 40ppm / °C-80ppm / °C, specifically, including but not limited to any point value among 40ppm / °C, 50ppm / °C, 60ppm / °C, 70ppm / °C, 80ppm / °C or a range between any two values.

[0042] In one embodiment, the material of the thermally expandable polymer substrate 301 includes but is not limited to at least one of epoxy resin, polyacrylate, polyimide, polyvinyl acetate, ethylene-propylene rubber, acrylonitrile-butadiene-styrene copolymer, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, biphenyl polyimide, and polycarbonate, and is preferably at least one of epoxy resin, polyacrylate, polyimide, polyvinyl acetate, ethylene-propylene rubber, acrylonitrile-butadiene-styrene copolymer, ethylene-vinyl acetate copolymer, and ethylene-ethyl acrylate copolymer.

[0043] Preferably, the mass ratio of the metal peroxide 302 to the negative electrode active material in the negative electrode active material layer 20 is 1:140-1:160, specifically, including but not limited to any point value among 1:140, 1:145, 1:150, 1:155, 1:160 or any range value between two thereof.

[0044] It should be noted that the present invention does not limit the specific material of the negative electrode active material in the negative electrode active material layer 20 , and existing negative electrode active materials such as graphite, silicon-based materials, silicon-carbon composite materials, etc. may be used.

[0045] In one embodiment, the negative electrode active material layer 20 also includes a binder and a conductive agent. Specifically, the binder includes but is not limited to at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-fluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin; the conductive agent includes but is not limited to at least one of conductive carbon black, carbon nanotubes, graphene and carbon nanofibers.

[0046] The negative electrode plate of the present invention can be prepared by a method commonly used in the art, or by any existing technology.

[0047] In one embodiment, the present invention provides a method for preparing the negative electrode sheet as described above, comprising the following steps:

[0048] S1, preparing negative electrode slurry and placing it on the surface of negative electrode current collector to form a negative electrode slurry layer;

[0049] S2, mixing heat-expandable high molecular polymer powder, metal peroxide powder and conductive glue and placing them on the surface of the negative electrode slurry layer, and obtaining the negative electrode plate after drying and pressing.

[0050] In step S1 , the specific steps of preparing the negative electrode slurry include: dispersing the negative electrode active material, the binder, the conductive agent or any other components in a solvent to form the negative electrode slurry.

[0051] Preferably, the mass ratio of the negative electrode active material, the binder and the conductive agent is (91-92.6):(6.0-6.6):(1.5-1.8).

[0052] Specifically, the negative electrode active material includes but is not limited to at least one of graphite, silicon-based materials, and silicon-carbon composite materials; the binder includes but is not limited to at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-fluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin; the conductive agent includes but is not limited to at least one of conductive carbon black (SP), carbon nanotubes, graphene and carbon nanofibers.

[0053] The negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil or aluminum foil may be used. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material on a polymer material substrate. Optionally, the metal material may include but is not limited to one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. Optionally, the polymer material substrate may include but is not limited to one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0054] Preferably, the negative electrode slurry is placed on the surface of the negative electrode current collector by coating. More preferably, the coating thickness of the negative electrode slurry is 125 μm-150 μm.

[0055] In step S2, preferably, the heat-expandable polymer powder and the metal peroxide powder are prepared according to a mass ratio of the metal peroxide powder to the negative electrode active material of 1:140-1:160 and a mass ratio of the metal peroxide powder to the heat-expandable polymer powder of 1:2.5-1:3.5.

[0056] Preferably, the mixed slurry is placed on the surface of the negative electrode slurry layer by coating. More preferably, the coating thickness of the mixed slurry is 10 μm-20 μm.

[0057] Preferably, the drying temperature is 55° C.-65° C., and the drying time is 7 h-9 h. It is understood that during the drying process, as the conductive glue in the mixed slurry evaporates, a protective layer is formed on the surface of the negative electrode current collector.

[0058] The present invention provides a battery, comprising the negative electrode plate as described above, wherein the protective layer in the negative electrode plate faces the positive electrode plate.

[0059] It can be understood that the battery is mainly composed of the above-mentioned negative electrode plate, positive electrode plate, separator and electrolyte.

[0060] Among them, the positive electrode plate, separator and electrolyte can be made of any commonly used materials in the field, or materials that can be obtained according to the prior art, and the present invention is not limited to this. For example, the positive electrode plate preferably includes a positive electrode collector and a positive electrode active material stacked on the surface of the positive electrode collector, wherein the positive electrode active material includes but is not limited to lithium iron phosphate.

[0061] The present invention also provides an electrical device, comprising the battery as described above.

[0062] The above-mentioned electrical equipment includes any equipment that uses the above-mentioned battery, such as electric vehicles, energy storage systems, electronic products, etc., but is not limited thereto.

[0063] The negative electrode sheet, preparation method and application thereof will be further described by the following specific examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. If no specific conditions are specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are followed. The reagents or instruments used without indicating the manufacturer are all conventional products that can be purchased commercially.

[0064] Example 1

[0065] 92.0 g of artificial graphite, 6.6 g of PVDF, 1.8 g of SP and 100 g of N-methylpyrrolidone (NMP) were evenly mixed to prepare a negative electrode slurry. The coating thickness was adjusted to about 125 μm and coated on the surface of the copper foil to form a negative electrode slurry layer.

[0066] 1.8g of epoxy resin (thermal expansion coefficient is 50ppm / ℃) and 0.6g of sodium peroxide are ball-milled into powder, mixed evenly with 2g of conductive glue to form a mixed slurry, and the coating thickness is adjusted to about 10μm. It is coated on the surface of the negative electrode slurry layer, and then placed in a vacuum oven at 60℃ for 8 hours. Then, a roller press is used for multiple rolling to obtain a negative electrode sheet.

[0067] Example 2

[0068] 91.5 g of artificial graphite, 6.5 g of PVDF, 1.6 g of SP and 10 g of N-methyl-2-pyrrolidone (NMP) were evenly mixed to prepare a negative electrode slurry. The coating thickness was adjusted to about 135 μm and coated on the surface of the copper foil to form a negative electrode slurry layer.

[0069] 1.5g of polyimide (thermal expansion coefficient is 40ppm / ℃) and 0.6g of potassium peroxide are ball-milled into powder, mixed evenly with 2g of conductive glue to form a mixed slurry, and the coating thickness is adjusted to about 15μm. It is coated on the surface of the negative electrode slurry layer, and then placed in a vacuum oven at 50℃ for 7 hours. Then, it is rolled several times using a roller press to obtain a negative electrode sheet.

[0070] Example 3

[0071] 91.0 g of artificial graphite, 6.0 g of PVDF, 1.5 g of SP and 10 g of N-methyl-2-pyrrolidone (NMP) were mixed evenly to prepare a negative electrode slurry. The coating thickness was adjusted to about 150 μm and coated on the surface of the copper foil to form a negative electrode slurry layer.

[0072] 2.1g of polyacrylate (thermal expansion coefficient is 80ppm / ℃) and 0.6g of sodium peroxide are ball-milled into powder, mixed evenly with 2g of conductive glue to form a mixed slurry, and the coating thickness is adjusted to about 20μm. It is coated on the surface of the negative electrode slurry layer, and then placed in a vacuum oven at 55℃ for 9 hours. Then, it is rolled several times using a roller press to obtain a negative electrode sheet.

[0073] Example 4

[0074] The negative electrode slurry layer was prepared in the same manner as in Example 1.

[0075] 1.8g of epoxy resin (thermal expansion coefficient is 50ppm / ℃) and 0.6g of sodium peroxide are ball-milled into powder, mixed evenly with 2g of conductive glue to form a mixed slurry, the coating thickness is adjusted to about 5μm, coated on the surface of the negative electrode slurry layer, and then placed in a vacuum oven at 60℃ for 8 hours, and then rolled several times using a roller press to obtain a negative electrode sheet.

[0076] Example 5

[0077] The negative electrode slurry layer was prepared in the same manner as in Example 1.

[0078] 1.8g of epoxy resin (thermal expansion coefficient is 50ppm / ℃) and 0.6g of sodium peroxide are ball-milled into powder, mixed evenly with 2g of conductive glue to prepare a mixed slurry, and the coating thickness is adjusted to about 25μm. It is coated on the surface of the negative electrode slurry layer, and then placed in a vacuum oven at 60℃ for 8 hours. Then, a roller press is used for multiple rolling to obtain a negative electrode sheet.

[0079] Example 6

[0080] The negative electrode slurry layer was prepared in the same manner as in Example 1.

[0081] 1.8g of epoxy resin (thermal expansion coefficient is 50ppm / ℃) and 0.3g of sodium peroxide are ball-milled into powder, mixed evenly with 2g of conductive glue to form a mixed slurry, the coating thickness is adjusted to about 10μm, coated on the surface of the negative electrode slurry layer, and then placed in a vacuum oven at 60℃ for 8 hours, and then rolled several times using a roller press to obtain a negative electrode sheet.

[0082] Example 7

[0083] The negative electrode slurry layer was prepared in the same manner as in Example 1.

[0084] 1.8g of epoxy resin (thermal expansion coefficient is 50ppm / ℃) and 0.9g of sodium peroxide are ball-milled into powder, mixed evenly with 2g of conductive glue to form a mixed slurry, the coating thickness is adjusted to about 10μm, coated on the surface of the negative electrode slurry layer, and then placed in a vacuum oven at 60℃ for 8 hours, and then rolled several times using a roller press to obtain a negative electrode sheet.

[0085] Example 8

[0086] The negative electrode slurry layer was prepared in the same manner as in Example 1.

[0087] 1.8g of biphenyl polyimide (thermal expansion coefficient is 5ppm / ℃) and 0.6g of sodium peroxide are ball-milled into powder, mixed evenly with 2g of conductive glue to form a mixed slurry, and the coating thickness is adjusted to about 10μm. It is coated on the surface of the negative electrode slurry layer, and then placed in a vacuum oven at 60℃ for 8 hours. Then, a roller press is used for multiple rolling to obtain a negative electrode sheet.

[0088] Example 9

[0089] The negative electrode slurry layer was prepared in the same manner as in Example 1.

[0090] 1.8g of polycarbonate (thermal expansion coefficient is 150ppm / ℃) and 0.6g of sodium peroxide are ball-milled into powder, mixed evenly with 2g of conductive glue to form a mixed slurry, the coating thickness is adjusted to about 10μm, coated on the surface of the negative electrode slurry layer, and then placed in a vacuum oven at 60℃ for 8 hours, and then rolled several times using a roller press to obtain a negative electrode sheet.

[0091] Example 10

[0092] The negative electrode slurry layer was prepared in the same manner as in Example 1.

[0093] 1.8g of epoxy resin (thermal expansion coefficient is 50ppm / ℃) and 0.6g of calcium peroxide are ball-ground into powder, mixed evenly with 2g of conductive glue to form a mixed slurry, the coating thickness is adjusted to about 10μm, coated on the surface of the negative electrode slurry layer, and then placed in a vacuum oven at 60℃ for 8 hours, and then rolled several times using a roller press to obtain a negative electrode sheet.

[0094] Comparative Example 1

[0095] The difference between Comparative Example 1 and Example 1 is that after the negative electrode slurry layer is formed, it is directly dried and roll-pressed to obtain a negative electrode sheet.

[0096] Comparative Example 2

[0097] The difference between Comparative Example 2 and Example 1 is that an equal amount of aluminum oxide is used instead of sodium peroxide.

[0098] Comparative Example 3

[0099] The difference between Comparative Example 3 and Example 1 is that an equal amount of silicon dioxide is used instead of sodium peroxide.

[0100] Comparative Example 4

[0101] The difference between Comparative Example 4 and Example 1 is that an equal amount of sodium hypochlorite is used instead of sodium peroxide.

[0102] Comparative Example 5

[0103] The difference between Comparative Example 5 and Example 1 is that an equal amount of sodium persulfate is used instead of sodium peroxide.

[0104] The negative electrode sheets prepared in Examples 1 to 10 were tested, and the results are shown in Table 1.

[0105] Table 1

[0106]

[0107] The negative electrode sheets prepared in Examples 1 to 10 and Comparative Examples 1 to 5 were assembled with the positive electrode sheets (lithium iron phosphate), a 12 μm PE separator, and a commercially purchased electrolyte into soft-pack cells: the positive electrode sheets, the negative electrode sheets, and the separator were made into bare cells by winding, packaged with aluminum-plastic film, injected with electrolyte, and packaged into soft-pack cells after formation, and safety tests and DC internal resistance tests were carried out. The results are shown in Table 2.

[0108] (1) Safety test: 10 soft-pack batteries were prepared, 5 of which were subjected to needle puncture test and 5 were subjected to interface lithium deposition analysis after 100 cycles of 3C charging.

[0109] (2) DC internal resistance test: Measure the DC internal resistance of 10 battery cells and take the average value.

[0110] Table 2

[0111]

[0112] In combination with Table 1 and Table 2, by comparing Examples 1 to 5, it can be seen that when the thickness of the coating protective layer is low, when a short circuit occurs, the effect of the protective layer in isolating the positive and negative electrodes is weakened; when the thickness of the coating protective layer is high, it can play a better role in preventing internal short circuits, but at the same time it will increase the DC internal resistance of the battery cell and reduce the fast charging performance of the battery cell. Therefore, by adjusting the coating thickness so that the thickness of the protective layer is 5%-15% of the thickness of the negative electrode active material layer, it can not only achieve the protection of preventing direct contact between the positive and negative electrodes, but also ensure that the DC internal resistance is low, so that the battery has a large current fast charging capability.

[0113] By comparing Examples 1 to 3 and Examples 6 and 7, it can be seen that when the content of sodium peroxide in the protective layer is low, the inhibitory effect on fast charging and lithium deposition is weakened; when the content of sodium peroxide in the protective layer is high, the inhibitory effect on fast charging and lithium deposition is better, but at the same time, excessive sodium peroxide will increase the DC internal resistance of the battery cell and reduce the fast charging performance of the battery cell. Therefore, by adjusting the sodium peroxide content in the protective layer to 15%-30%, both the inhibition of fast charging and lithium deposition can be achieved and a lower DC internal resistance of the battery cell can be achieved.

[0114] According to Table 2, the negative electrode plates prepared in Examples 1 to 10 have good effects in preventing the internal short circuit from developing into thermal runaway and fast charging and lithium precipitation, and improve the safety performance of the battery. However, in Comparative Example 1, the protective layer was not coated, and 100% of the battery cells failed the safety test, and the lithium precipitation rate was as high as about 80%; the protective layers of Comparative Examples 2 and 3 used ceramic materials, and the ceramic materials could not achieve the function of isolating the positive and negative electrodes under the condition of acupuncture, and 100% of the battery cells failed the safety test; the protective layers of Comparative Examples 4 and 5 used different oxides, and different metal peroxides had different effects on the inhibition of fast charging and lithium precipitation, and also affected the DC internal resistance of the battery cells, and thus affected the fast charging performance, among which sodium peroxide had a better inhibitory effect on fast charging and lithium precipitation than sodium hypochlorite and sodium persulfate, and the DC internal resistance of the battery cells using sodium peroxide was less than the DC internal resistance of the battery cells using sodium persulfate and sodium hypochlorite. In summary, the present invention has the best effect in terms of inhibition of fast charging and lithium precipitation and low DC internal resistance.

[0115] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0116] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A negative electrode plate, characterized in that: The negative electrode sheet includes a negative electrode current collector, and a negative electrode active material layer and a protective layer stacked on the surface of the negative electrode current collector; Wherein, the protective layer includes a thermally expandable high molecular polymer substrate and a metal peroxide distributed in the thermally expandable high molecular polymer substrate. The thickness of the protective layer is 5%-15% of the thickness of the negative electrode active material layer. The metal peroxide includes at least one of sodium peroxide and potassium peroxide. The material of the thermally expandable high molecular polymer substrate includes at least one of epoxy resin, polyacrylate, polyimide, polyvinyl acetate, ethylene-propylene rubber, acrylonitrile-butadiene-styrene copolymer, ethylene-vinyl acetate copolymer, and ethylene-ethyl acrylate copolymer.

2. The negative electrode sheet according to claim 1, characterized in that: The thickness of the protective layer is 10 μm-20 μm; And / or, the thickness of the negative electrode active material layer is 125 μm-150 μm.

3. The negative electrode sheet according to claim 1, characterized in that: The mass fraction of the metal peroxide in the protective layer is 15%-30%; And / or, in the composite layer composed of the negative electrode active material layer and the protective layer, the density of the metal peroxide is 15.5 mg / cm 3 -18.5mg / cm 3 .

4. The negative electrode sheet according to claim 1, characterized in that: The thermal expansion coefficient of the thermal expansion macromolecular polymer substrate is 40ppm / °C-80ppm / °C.

5. The negative electrode sheet according to claim 1, characterized in that: The mass ratio of the metal peroxide to the negative electrode active material in the negative electrode active material layer is 1:140-1:

160.

6. A method for preparing a negative electrode sheet according to any one of claims 1 to 5, characterized in that: The steps include: Prepare negative electrode slurry and place it on the surface of negative electrode current collector to form a negative electrode slurry layer; The heat-expandable high molecular polymer powder, metal peroxide powder and conductive glue are mixed and placed on the surface of the negative electrode slurry layer, and the negative electrode plate is obtained after drying and pressing.

7. A battery, characterized in that: It comprises the negative electrode sheet as claimed in any one of claims 1 to 5, and the protective layer in the negative electrode sheet faces the positive electrode sheet.

8. An electrical device, characterized in that: Comprising the battery as claimed in claim 7.

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