Negative plate and preparation method thereof, battery and electric equipment

Abstract

The invention provides a negative plate and a preparation method thereof, a battery and electric equipment. The negative plate comprises a negative plate substrate, a lithium supplementing layer and a coating positioned between the negative plate substrate and the lithium supplementing layer, the coating includes an inorganic oxide. According to the negative electrode plate provided by the invention, the coating is arranged between the negative electrode plate substrate and the lithium supplementing layer, the coating comprises the inorganic oxide, and the coating can prevent lithium from reacting with the negative electrode active material in the absence of electrolyte, so that the heating temperature of the negative electrode plate is reduced, and the potential safety hazard is reduced. And after the electrolyte is injected, the inorganic oxide can construct a lithium ion path to finish pre-lithiation, so that the consumption of active lithium is reduced, the discharge energy of the battery is improved, and the lithium supplementing efficiency is improved.

Description

Technical Field

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

[0002] Negative electrode pre-lithiation technology can compensate for the loss of active lithium caused by SEI film formation and side reactions in the entire battery, thereby improving the battery's energy density and cycle life. However, after lithium replenishment, the lithium in the negative electrode will continue to diffuse and react with the negative electrode active material, releasing heat, posing a safety hazard, reducing the battery's discharge energy, and lowering the efficiency of lithium replenishment. Summary of the Invention

[0003] The main purpose of the present invention is to provide a negative electrode sheet that can solve the heating problem of the battery, reduce safety hazards, increase the discharge energy of the battery, and improve the lithium replenishment efficiency.

[0004] The present invention also provides a method for preparing a negative electrode sheet, which can prepare the negative electrode sheet and has simple process and low cost.

[0005] The present invention also provides a battery comprising the above-mentioned negative electrode sheet. Therefore, the battery has a lower heating temperature, higher safety, higher discharge energy, and higher lithium replenishment efficiency.

[0006] The present invention also provides an electrical device comprising the above-mentioned battery. Therefore, the performance of the battery associated with the electrical device is relatively excellent.

[0007] In a first aspect, the present invention provides a negative electrode sheet, comprising a negative electrode sheet substrate, a lithium replenishing layer, and a coating located between the negative electrode sheet substrate and the lithium replenishing layer;

[0008] The coating includes an inorganic oxide.

[0009] In the negative electrode sheet as described above, the inorganic oxide has a porous structure.

[0010] In the negative electrode sheet as described above, the inorganic oxide includes at least one of an oxide containing silicon, an oxide containing aluminum, and an oxide containing silicon and aluminum.

[0011] For the negative electrode sheet as described above, the thickness of the coating layer is 100 nm to 5000 nm, preferably 1000 nm to 4000 nm.

[0012] For the negative electrode sheet as described above, the mass proportion of the inorganic oxide in the coating layer is 86%-96%.

[0013] The negative electrode sheet as described above, wherein the silicon-containing oxide comprises silicon dioxide;

[0014] and / or, the aluminum-containing oxide comprises aluminum oxide;

[0015] And / or, the oxide containing silicon and aluminum comprises an aluminosilicate, and the aluminosilicate comprises a zeolite.

[0016] For the negative electrode sheet as described above, the coating layer further includes a binder and a conductive agent.

[0017] The negative electrode sheet as described above, wherein the binder comprises at least one of polyvinylidene fluoride, styrene-butadiene rubber, carboxymethyl cellulose, and polytetrafluoroethylene;

[0018] And / or, the conductive agent includes at least one of carbon nanotubes, carbon black, acetylene black, and graphene.

[0019] In the negative electrode sheet as described above, the binder in the coating accounts for 2%-5% by mass;

[0020] And / or, the conductive agent in the coating accounts for 2%-12% by mass.

[0021] The negative electrode sheet as described above, wherein the negative electrode sheet substrate comprises a graphite negative electrode and / or a silicon negative electrode;

[0022] And / or, the lithium replenishing layer includes lithium powder and / or lithium foil.

[0023] In a second aspect, the present invention provides a method for preparing the negative electrode sheet as described above, comprising the following steps:

[0024] Providing the negative electrode substrate;

[0025] Disposing a coating slurry comprising the inorganic oxide on the negative electrode substrate;

[0026] The lithium supplement layer is compounded to obtain the negative electrode sheet.

[0027] In the above-mentioned method for preparing the negative electrode sheet, the coating slurry further includes a binder and a conductive agent.

[0028] In a third aspect, the present invention provides a battery comprising the negative electrode sheet as described above or the negative electrode sheet prepared by the negative electrode sheet preparation method as described above.

[0029] In a fourth aspect, the present invention provides an electrical device comprising the battery as described above.

[0030] The negative electrode sheet provided by the present invention has a coating layer disposed between the negative electrode substrate and the lithium replenishment layer. The coating comprises an inorganic oxide. In the absence of an electrolyte, the coating prevents lithium from reacting with the negative electrode active material, reducing the negative electrode sheet's heat generation temperature and mitigating safety risks. After the electrolyte is injected, the inorganic oxide creates a lithium ion pathway, completing pre-lithiation, reducing active lithium consumption, increasing the battery's discharge energy, and improving lithium replenishment efficiency. DETAILED DESCRIPTION

[0031] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0032] With the rapid development of portable electronic devices and electric vehicles, the use of lithium-ion batteries in mobile power sources has become increasingly common. However, to meet user demands for longer battery life and higher energy density, improving the energy density of lithium-ion batteries has become a major technical challenge. During the battery manufacturing process, the solid electrolyte interface (SEI) film formed during the initial charge and discharge cycle and other side reactions consume some active lithium, resulting in a decrease in the battery's initial coulombic efficiency and energy density.

[0033] Anode pre-lithiation technology is considered one of the effective methods to address this problem. By pre-introducing lithium into the anode material, lithium loss caused by SEI film formation and side reactions can be compensated, thereby improving the battery's initial coulombic efficiency and energy density. Among the various pre-lithiation methods, directly compounding metallic lithium on the anode is the most direct and effective. Commonly used lithium sources include lithium powder and lithium foil, which can provide sufficient lithium for pre-lithiation.

[0034] However, a key issue in the anode pre-lithiation process is thermal management. During the pre-lithiation process, lithium continuously diffuses and reacts with the anode active material, releasing heat. If this heat cannot be effectively dissipated, heat may accumulate during the winding of the lithium-replenished anode sheet, leading to "sheet burn." This not only results in significant loss of active lithium but can also cause more serious safety issues such as fire and explosion. This has significantly hindered the commercial application of anode pre-lithiation technology.

[0035] Based on this, in a first aspect, the present invention provides a negative electrode sheet, comprising a negative electrode sheet substrate and a lithium replenishing layer, and a coating located between the negative electrode sheet substrate and the lithium replenishing layer; the coating comprises an inorganic oxide.

[0036] It can be understood that the negative electrode substrate includes a negative electrode current collector and a negative electrode active material layer, and the lithium replenishing layer can be provided on one side or both sides of the negative electrode substrate. The coating is provided between the negative electrode substrate and the lithium replenishing layer.

[0037] The negative electrode sheet provided by the present invention has a coating disposed between the negative electrode sheet substrate and the lithium replenishment layer, and the coating includes an inorganic oxide. This negative electrode sheet can solve the problem of battery heating, reduce safety risks, and increase the battery's discharge energy and enhance lithium replenishment efficiency. This is because the inorganic oxide does not conduct lithium in the absence of an electrolyte. Therefore, after the negative electrode sheet substrate is replenished with lithium (i.e., the lithium replenishment layer is added), the coating prevents the lithium in the lithium replenishment layer from reacting with the negative electrode active material in the negative electrode sheet substrate, thereby reducing the temperature of the negative electrode sheet. After lithium replenishment, the negative electrode sheet does not have heating safety issues. After the electrolyte is injected, the inorganic oxide absorbs the electrolyte and can quickly conduct lithium ions. It forms a lithium ion path between the lithium replenishment layer and the negative electrode sheet substrate, so that lithium is gradually embedded in the negative electrode sheet substrate, completing pre-lithiation. In addition, the inorganic oxide promotes lithium ion desolvation, which can reduce battery polarization and improve battery performance.

[0038] At the same time, since the coating can prevent the lithium in the lithium replenishment layer from reacting with the negative electrode active material, the lithium replenishment layer can effectively compensate for the irreversible lithium loss during the first charge and discharge of the battery, reduce the loss of active lithium, increase the discharge energy of the battery, and improve the lithium replenishment efficiency.

[0039] The negative electrode sheet provided by the present invention comprises a coating between the negative electrode substrate and the lithium replenishment layer. The coating comprises an inorganic oxide. In the absence of an electrolyte, the coating prevents lithium from reacting with the negative electrode active material, reducing the negative electrode sheet's heat generation temperature and mitigating safety risks. After the electrolyte is injected, the inorganic oxide creates a lithium ion pathway, completing pre-lithiation, reducing active lithium loss, increasing the battery's discharge energy, and improving lithium replenishment efficiency.

[0040] In some embodiments of the present invention, the inorganic oxide has a porous structure. While isolating the negative electrode substrate from the lithium replenishment layer, it can also effectively absorb electrolyte, creating a lithium ion pathway between the lithium replenishment layer and the negative electrode substrate, achieving pre-lithiation. This reduces the negative electrode's heating temperature, reduces active lithium loss, increases the battery's discharge energy, and improves lithium replenishment efficiency.

[0041] Specifically, the inorganic oxide includes at least one of an oxide containing silicon, an oxide containing aluminum, and an oxide containing silicon and aluminum.

[0042] In some embodiments of the present invention, the thickness of the coating is 100 nm-5000 nm, for example, it can be 100 nm, 500 nm, 1000 nm, 2000 nm, 3000 nm, 4000 nm, 5000 nm or any two thereof, preferably 1000 nm-4000 nm.

[0043] The thickness of the coating in the present invention is within the above range, which can effectively isolate the negative electrode substrate and the lithium replenishment layer, further reduce the heating temperature of the negative electrode, reduce the loss of active lithium, increase the discharge energy of the battery, and improve the lithium replenishment efficiency.

[0044] In some embodiments of the present invention, the inorganic oxide content of the coating ranges from 86% to 96% by weight, for example, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, or any combination thereof. This can further reduce the heating temperature of the negative electrode sheet, reduce active lithium loss, increase the battery's discharge energy, and enhance lithium replenishment efficiency.

[0045] In some embodiments of the present invention, the silicon-containing oxide comprises silicon dioxide.

[0046] In some embodiments, the aluminum-containing oxide includes aluminum oxide.

[0047] In some embodiments, the silicon and aluminum containing oxide comprises an aluminosilicate, and the aluminosilicate comprises a zeolite.

[0048] The zeolite in the present invention can be Li-X zeolite, and the silica can be porous silica. The porous structure of alumina, aluminosilicate, and silica effectively absorbs electrolyte while isolating the negative electrode substrate from the lithium replenishment layer, creating a lithium ion pathway between the lithium replenishment layer and the negative electrode substrate, thereby achieving pre-lithiation. This can further reduce the heating temperature of the negative electrode, reduce active lithium loss, increase the battery's discharge energy, and enhance lithium replenishment efficiency.

[0049] The preparation method of Li-X zeolite comprises the following steps:

[0050] Immerse Na-X zeolite with a particle size of 30nm-1000nm in a 0.2mol / L-5mol / L lithium hydroxide solution for 2h-72h, filter it, and then immerse it in a 0.2mol / L-5mol / L aluminum hydroxide solution for 6h-72h, repeatedly 2-5 times; after the final filtration, rinse it with deionized water and dry it in a 40℃-110℃ drying oven for 6h-72h.

[0051] In some embodiments of the present invention, the coating further comprises a binder and a conductive agent. The binder helps maintain the integrity of the coating during the battery's charge-discharge cycle, preventing material shedding or separation. The conductive agent can enhance electronic conductivity between the lithium-supplementing layer and the negative electrode substrate, improving the battery's rate performance.

[0052] In some embodiments of the present invention, the binder includes at least one of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and polytetrafluoroethylene (PTFE), which can firmly combine the inorganic oxide and the conductive agent to form a stable coating, which is beneficial to maintaining the integrity of the coating during the battery charge and discharge cycle and preventing the material from falling off or separating.

[0053] In some embodiments of the present invention, the conductive agent includes at least one of carbon nanotubes, carbon black, acetylene black, and graphene, which can improve the electronic conductivity between the lithium supplement layer and the negative electrode substrate, promote the transmission of electrons in the electrode, improve the rate performance of the battery, and enable the battery to be quickly charged and discharged at high current density without significantly reducing the capacity.

[0054] In some embodiments of the present invention, the binder in the coating comprises 2% to 5% by weight, for example, 2%, 3%, 4%, 5%, or any combination thereof. An appropriate amount of binder can ensure the mechanical strength and structural integrity of the electrode and minimize the impact on electrical conductivity and ion transport.

[0055] In some embodiments, the conductive agent in the coating comprises 2% to 12% by weight, for example, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, or any combination thereof. An appropriate amount of conductive agent can improve the conductivity of the electrode, ensuring rapid electron transport and allowing lithium to be rapidly embedded in the negative electrode substrate after injection, completing pre-lithiation.

[0056] In some embodiments of the present invention, the negative electrode substrate includes a graphite negative electrode and / or a silicon negative electrode.

[0057] In some embodiments, the lithium replenishing layer includes lithium powder and / or lithium foil.

[0058] The negative electrode substrate in the present invention includes a graphite negative electrode and / or a silicon negative electrode. Under the action of the coating, the heating temperature of the negative electrode sheet can be further reduced, the loss of active lithium can be reduced, the discharge energy of the battery can be increased, and the lithium replenishment efficiency can be improved.

[0059] The lithium replenishing layer in the present invention includes lithium powder and / or lithium foil, which can provide a lithium source and effectively compensate for lithium loss during battery cycling, thereby increasing the discharge energy of the battery and improving the lithium replenishing efficiency.

[0060] In a second aspect, the present invention provides a method for preparing the negative electrode sheet as described above, comprising the following steps:

[0061] Providing a negative electrode substrate;

[0062] Disposing a coating slurry including an inorganic oxide on a negative electrode substrate;

[0063] The composite lithium supplement layer is formed to obtain a negative electrode sheet.

[0064] In the present invention, a coating slurry comprising an inorganic oxide is applied to a negative electrode substrate, and then a lithium replenishing layer is added to obtain the negative electrode sheet provided by the first aspect of the present invention. Specifically, the negative electrode sheet comprises a negative electrode substrate, a lithium replenishing layer, and a coating layer disposed between the negative electrode substrate and the lithium replenishing layer; the coating layer comprises an inorganic oxide. Furthermore, the negative electrode sheet exhibits a low heat generation temperature, which can reduce active lithium loss, increase battery discharge energy, and enhance lithium replenishment efficiency.

[0065] Specifically, the negative electrode active material, conductive agent and binder can be mixed in a certain mass ratio, a certain amount of deionized water can be added, and the mixture can be stirred evenly under the action of a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry is then coated on the negative electrode current collector and dried to obtain a negative electrode sheet substrate.

[0066] The negative electrode current collector of the present invention can be made of copper foil, and the thickness of the negative electrode current collector can be 4 μm-10 μm.

[0067] The inorganic oxide is then added to a certain amount of N-methylpyrrolidone (NMP) and stirred evenly in a vacuum mixer to obtain a coating slurry. This coating slurry is evenly coated on the surface of the negative electrode substrate, away from the negative electrode current collector, and dried. Finally, the electrode is roller-pressed, coated with a lithium supplement layer, and wound to obtain the negative electrode sheet.

[0068] In some embodiments of the present invention, the coating slurry further comprises a binder and a conductive agent. The mass ratio of the inorganic oxide, the binder, and the conductive agent may be (86-96):(2-5):(2-12), for example, 86:2:2, 86:2:12, 90:2:8, 94:2:4, 96:2:2, or any combination thereof.

[0069] In the negative electrode sheet preparation method of the present invention, the slurry also includes a binder and a conductive agent. The binder helps maintain the integrity of the coating during the battery's charge and discharge cycles, preventing material shedding or separation. The conductive agent improves the electronic conductivity between the lithium replenishment layer and the negative electrode substrate, thereby enhancing the battery's rate performance.

[0070] The mass ratio of the inorganic oxide, the binder and the conductive agent is within the above range, which can make the mass ratio of the inorganic oxide, the binder and the conductive agent in the coating of the prepared negative electrode sheet appropriate, further isolate the negative electrode sheet substrate and the lithium replenishing layer, reduce the heating temperature of the negative electrode sheet, increase the discharge energy of the battery, and improve the lithium replenishing efficiency.

[0071] In a third aspect, the present invention provides a battery comprising the negative electrode sheet as described above or a negative electrode sheet prepared by the negative electrode sheet preparation method as described above. The battery has the advantages corresponding to the above negative electrode sheet, which will not be described in detail.

[0072] The battery of the present invention includes, in addition to the negative electrode sheet, a separator, a positive electrode sheet, and an electrolyte. The composition of the positive electrode sheet can refer to conventional positive electrode sheets in the art, and the separator can also be a separator commonly used in the art, such as PP film, PE film, etc.

[0073] The battery of the present invention can be prepared by conventional methods in the field. Specifically, the positive electrode sheet, the separator and the negative electrode sheet can be stacked in sequence, and then the battery core can be obtained through a lamination or winding process, and then through baking, liquid injection, formation, packaging and other processes to obtain the above-mentioned battery.

[0074] The batteries of the present application may include battery cells, battery modules, and battery packs. In some embodiments, battery cells may be assembled into a battery module, which may contain one or more battery cells, with the specific number selected by those skilled in the art based on the application and capacity of the battery module. In some embodiments, battery modules may also be assembled into a battery pack, which may contain one or more battery modules, with the specific number selected by those skilled in the art based on the application and capacity of the battery pack.

[0075] There is no particular restriction on the specific type of battery in this application. For example, from the perspective of shape, the battery includes but is not limited to square shell batteries, soft pack batteries and cylindrical batteries, etc., and this application does not impose any particular restrictions. From the perspective of the core structure, the core of the battery can be a wound core (i.e., the positive electrode sheet, the negative electrode sheet and the separator are stacked and then wound to form the core), or it can be a laminated core (i.e., multiple positive electrode sheets, negative electrode sheets and separators are stacked to form the core). The outer shell can be a hard shell (such as a steel shell, a hard plastic shell, etc.), or a soft shell (such as an aluminum plastic film, a bag-type soft shell, etc.). This application does not impose any particular restrictions.

[0076] In a fourth aspect, the present invention provides an electrical device comprising the battery as described above. The electrical device has advantages corresponding to those of the negative electrode sheet described above, which will not be described in detail.

[0077] The electrical equipment of the present invention can be conventional electrical equipment in the field, such as power equipment (such as electric vehicles), electronic equipment (such as computers, mobile phones, digital cameras, printers, fax machines, etc.), wearable devices (such as watches, bracelets, VR glasses, etc.), household appliances (such as air conditioners, refrigerators, washing machines, microwave ovens, etc.), etc., without special restrictions.

[0078] The technical solution of the present invention is further described below with reference to specific embodiments.

[0079] Example 1

[0080] The method for preparing the negative electrode sheet of this embodiment includes the following steps:

[0081] Preparation of Li-X zeolite

[0082] Immerse 200nm Na-X zeolite in 1mol / L lithium hydroxide solution for 24h, filter it and then immerse it in 1mol / L aluminum hydroxide solution for 24h, for three times in a row; after the final filtration, rinse it with deionized water and dry it in an 80℃ drying oven for 24h.

[0083] Preparation of negative electrode sheet

[0084] 1) The negative electrode active material artificial graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 94:2:2:2, a certain amount of deionized water was added, and the mixture was stirred evenly in a vacuum mixer to obtain a negative electrode slurry; the negative electrode slurry was evenly coated on a negative electrode current collector copper foil with a thickness of 8 μm and dried to obtain a negative electrode sheet substrate.

[0085] 2) Li-X zeolite, binder polyvinylidene fluoride (PVDF) and conductive agent carbon nanotubes were mixed in a mass ratio of 90:2:8, and a certain amount of N-methylpyrrolidone (NMP) was added. The mixture was stirred evenly in a vacuum mixer to obtain a coating slurry. The coating slurry was evenly coated on the surface of the negative electrode substrate away from the negative electrode current collector using an inkjet printing process and dried. The inkjet printing ink volume was 1g / m 2 .

[0086] 3) Finally, the electrode sheet is rolled, laminated with 2μm-thick lithium foil, and wound to form the negative electrode sheet. The negative electrode sheet consists of a substrate, a lithium-supplementing layer, and a coating layer between the substrate and the lithium-supplementing layer. The coating comprises a porous inorganic oxide Li-X zeolite, a binder (PVDF), and a conductive agent (carbon nanotubes). The inorganic oxide accounts for 90% by weight of the coating, the binder for 2%, and the conductive agent for 8%. The coating is 100nm thick.

[0087] Example 2

[0088] The preparation method of the negative electrode sheet of Example 2 is basically the same as that of Example 1, except that in step 2), the inkjet printing ink volume is increased to 5g / m 2 The thickness of the prepared coating is 500 nm.

[0089] Example 3

[0090] The preparation method of the negative electrode sheet of Example 3 is basically the same as that of Example 1, except that in step 2), the inkjet printing ink volume is increased to 10 g / m 2 The thickness of the prepared coating is 1000 nm.

[0091] Example 4

[0092] The preparation method of the negative electrode sheet of Example 4 is basically the same as that of Example 1, except that in step 2), the inkjet printing ink volume is increased to 20 g / m 2 The thickness of the prepared coating is 2000 nm.

[0093] Example 5

[0094] The preparation method of the negative electrode sheet of Example 5 is basically the same as that of Example 1, except that in step 2), the inkjet printing ink volume is increased to 30 g / m 2 The thickness of the prepared coating is 3000 nm.

[0095] Example 6

[0096] The preparation method of the negative electrode sheet of Example 6 is basically the same as that of Example 1, except that in step 2), the inkjet printing ink volume is increased to 40 g / m 2 The thickness of the prepared coating is 4000 nm.

[0097] Example 7

[0098] The preparation method of the negative electrode sheet of Example 7 is basically the same as that of Example 1, except that in step 2), the inkjet printing ink volume is increased to 50g / m 2 The thickness of the prepared coating is 5000 nm.

[0099] Example 8

[0100] The preparation method of the negative electrode sheet of Example 8 is basically the same as that of Example 1, except that in step 2), the mass ratio of the inorganic oxide, the binder, and the conductive agent is changed to 86:2:12.

[0101] Example 9

[0102] The preparation method of the negative electrode sheet of Example 9 is basically the same as that of Example 1, except that in step 2), the mass ratio of the inorganic oxide, the binder, and the conductive agent is changed to 96:2:2.

[0103] Example 10

[0104] The preparation method of the negative electrode sheet of Example 10 is basically the same as that of Example 1, except that the inorganic oxide in step 2) is changed to porous silicon dioxide.

[0105] Example 11

[0106] The preparation method of the negative electrode sheet of Example 11 is basically the same as that of Example 1, except that the negative electrode active material in step 1) is changed to nano-silicon particles.

[0107] Comparative Example 1

[0108] The preparation methods of the negative electrode sheets of Comparative Example 1 and Example 1 are basically the same, except that step 2) is omitted, that is, no coating is provided between the lithium replenishing layer and the negative electrode sheet substrate.

[0109] Comparative Example 2

[0110] The preparation method for the negative electrode sheet of Comparative Example 2 is essentially the same as that of Example 1, except that in step 2), the binder polyvinylidene fluoride (PVDF) and the conductive agent carbon nanotubes are mixed in a mass ratio of 10:90, a certain amount of N-methylpyrrolidone (NMP) is added, and the mixture is stirred evenly in a vacuum mixer to obtain a coating slurry. The coating includes the binder and the conductive agent.

[0111] Test example:

[0112] 1) Preparation of positive electrode

[0113] The positive electrode active material (lithium iron phosphate LiFePO4), binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black are mixed in a mass ratio of 100:2.5:2.5, and a certain amount of N-methylpyrrolidone (NMP) is added. The mixture is stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on a positive electrode current collector aluminum foil with a thickness of 13μm and dried, and finally the positive electrode sheet is obtained by rolling and cutting.

[0114] 2) Preparation of electrolyte

[0115] In a nitrogen atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm, the organic solvents ethylene carbonate (EC), dimethyl carbonate (DMC), dimethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC:DMC:DEC:EMC = 1:1:1:1 to form a mixed solvent. The lithium salt LiPF6 was then slowly dissolved in the mixed organic solvent. The functional additive vinylene carbonate (VC) was then added and mixed thoroughly to obtain an electrolyte. Based on the total mass of the electrolyte, the mass percentage of the lithium salt LiPF6 was 16%, and the mass percentage of vinylene carbonate (VC) was 3%.

[0116] 3) Isolation film

[0117] The diaphragm is a PE-coated ceramic diaphragm with a thickness of 12µm.

[0118] 4) Lithium-ion battery preparation

[0119] The negative electrode sheet, separator, positive electrode sheet, and separator of the above embodiment and comparative example were stacked in order, fixed with high-temperature resistant tape, and then welded with the positive and negative electrode tabs. The battery cell was then encapsulated with aluminum-plastic film to obtain a battery cell. The battery cell was then injected with the corresponding prepared electrolyte and encapsulated.

[0120] 5) Formation

[0121] The assembled cells were aged at 45°C for one day and then charged at a constant current of 0.05C to a SOC of 10%. The cells were then charged at a constant current of 0.1C to 3.8V, then stopped charging and aged at 45°C for two days. This was followed by venting and capacity separation to obtain a lithium-supplemented lithium iron phosphate battery.

[0122] Heating temperature: Roll up the prepared negative electrode sheet with a length of 100m into a roll, then seal the negative electrode sheet in an insulating bag and measure the maximum temperature inside the negative electrode sheet for 24 hours, which is the heating temperature.

[0123] 1 / 3C discharge energy test: After the formed battery is cooled at 25℃ for 6h, it is discharged at 1 / 3C to 2V, and charged to 3.8V at 1 / 3C constant current and constant voltage with a cut-off current of 0.05C. The charge and discharge process is repeated three times, and the discharge energy of the third discharge is recorded as the battery 1 / 3C discharge energy.

[0124] Lithium replenishment efficiency: The increased capacity C (mAh) of the lithium-replenished battery compared to the unreplenished battery is related to the amount of lithium pre-stored in the negative electrode at 0% SOC. The sum of the total amount of lithium replenishment (mAh) divided by the total amount of lithium replenishment C0 (mAh) is the lithium replenishment efficiency, that is, lithium replenishment efficiency = .

[0125] The difference between the non-lithium-replenished battery and the lithium-replenished battery is that the non-lithium-replenished battery has no lithium-replenished layer on its negative electrode sheet, and other conditions are the same.

[0126] After the formed battery is cooled at 25°C for 6 hours, it is charged to 3.8V at a constant current and constant voltage of 1 / 3C, with a cut-off current of 0.05C, and discharged to 2V at 1 / 3C. This charge and discharge process is repeated three times, and the discharge capacity of the third discharge is recorded as the battery's 1 / 3C discharge capacity. The 1 / 3C discharge capacity of the lithium-supplemented battery is recorded as C1, and the 1 / 3C discharge capacity of the non-lithium-supplemented battery is recorded as C2. The increased capacity C=C1-C2;

[0127] The battery after the above test was discharged at 1 / 3C to 2V, and the battery was disassembled in an inert atmosphere. All the negative electrode sheets were taken out and sealed in a sample bag. A certain amount of water was injected into the sealed bag. The gas volume V (L) before and after the water injection was measured using the Archimedean principle. The active lithium content in the negative electrode was 2412.5×V. The active lithium content in the negative electrode of the lithium-supplemented battery is recorded as , the active lithium content in the negative electrode of the unsupplemented lithium battery is recorded as , replenish the amount of lithium stored in the negative electrode of the lithium battery at 0% SOC ;

[0128] The total amount of lithium replenishment C0 is equal to the area of ​​the negative electrode of the lithium replenishment battery (m 2 )×lithium supplement surface density (g / m 2 )×3860 (mAh / g).

[0129] Table 1

[0130]

[0131] As shown in Table 1, compared to the comparative example, the negative electrode sheet provided by the present invention has a coating layer between the negative electrode substrate and the lithium replenishment layer. This coating comprises an inorganic oxide. In the absence of an electrolyte, this coating prevents lithium from reacting with the negative electrode active material, reducing the negative electrode sheet's heat generation temperature and mitigating safety risks. After electrolyte injection, the inorganic oxide creates a lithium ion pathway, completing pre-lithiation, reducing active lithium consumption, increasing the battery's discharge energy, and improving lithium replenishment efficiency.

[0132] From the test results of Examples 1-4, it can be seen that as the coating thickness increases, the heating temperature of the negative electrode sheet gradually decreases, the discharge energy gradually increases, and the lithium replenishment efficiency gradually improves. This is because the coating thickness gradually increases within a certain range, which can effectively isolate the contact between the negative electrode active material and the lithium replenishment layer, thereby reducing the consumption of active lithium by the negative electrode.

[0133] Compared with Examples 1, 2, and 7, the coating thickness of Examples 3-6 is between 1000 nm and 4000 nm, which can further reduce the heating temperature of the negative electrode sheet, increase the discharge energy, and improve the lithium replenishment efficiency.

[0134] Finally, it should be noted that those skilled in the art will readily identify other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. The present invention is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art not disclosed herein. The present invention is not limited to the precise structure described above and may be modified and altered in various ways without departing from the scope thereof. The scope of the present invention is limited solely by the appended claims.

Claims

1. A negative electrode sheet, characterized in that: It includes a negative electrode substrate and a lithium replenishing layer, and a coating located between the negative electrode substrate and the lithium replenishing layer; The coating includes an inorganic oxide.

2. The negative electrode sheet according to claim 1, characterized in that: The inorganic oxide has a porous structure.

3. The negative electrode sheet according to claim 1 or 2, characterized in that: The inorganic oxide includes at least one of an oxide containing silicon, an oxide containing aluminum, and an oxide containing silicon and aluminum.

4. The negative electrode sheet according to any one of claims 1 to 3, characterized in that: The thickness of the coating is 100 nm to 5000 nm, preferably 1000 nm to 4000 nm.

5. The negative electrode sheet according to any one of claims 1 to 4, characterized in that: The inorganic oxide in the coating accounts for 86%-96% by mass.

6. The negative electrode sheet according to claim 3, characterized in that: The silicon-containing oxide includes silicon dioxide; and / or, the aluminum-containing oxide comprises aluminum oxide; And / or, the oxide containing silicon and aluminum comprises an aluminosilicate, and the aluminosilicate comprises a zeolite.

7. The negative electrode sheet according to any one of claims 1 to 6, characterized in that: The coating also includes a binder and a conductive agent.

8. The negative electrode sheet according to claim 7, characterized in that: The binder comprises at least one of polyvinylidene fluoride, styrene-butadiene rubber, carboxymethyl cellulose and polytetrafluoroethylene; And / or, the conductive agent includes at least one of carbon nanotubes, carbon black, acetylene black, and graphene.

9. The negative electrode sheet according to claim 7 or 8, characterized in that: The mass proportion of the binder in the coating is 2%-5%; And / or, the conductive agent in the coating accounts for 2%-12% by mass.

10. The negative electrode sheet according to any one of claims 1 to 9, characterized in that: The negative electrode substrate includes a graphite negative electrode and / or a silicon negative electrode; And / or, the lithium replenishing layer includes lithium powder and / or lithium foil.

11. A method for preparing a negative electrode sheet according to any one of claims 1 to 10, characterized in that: The following steps are involved: Providing the negative electrode substrate; Disposing a coating slurry comprising the inorganic oxide on the negative electrode substrate; The lithium supplement layer is compounded to obtain the negative electrode sheet.

12. The method for preparing a negative electrode sheet according to claim 11, wherein: The coating slurry further includes a binder and a conductive agent.

13. A battery, characterized in that: A negative electrode sheet comprising the negative electrode sheet according to any one of claims 1 to 10 or a negative electrode sheet prepared by the preparation method of the negative electrode sheet according to claim 11 or 12.

14. An electrical device, characterized in that: Including the battery according to claim 13.

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