Negative plates, lithium batteries, and electrical equipment

Abstract

A negative electrode plate including a negative electrode current collector and a capacity supply layer, a conductive bonding layer, and a fast-ion conductor layer stacked in this order on at least one side of the negative electrode current collector, wherein the capacity supply layer comprises a first negative electrode active material, a first binder, and a first conductive agent, and the fast-ion conductor layer comprises a carbon active material, a lithium superionic conductor, a second binder, and a second conductive agent, and the specific capacity of the first negative electrode active material is greater than the specific capacity of the carbon active material. A lithium battery including the negative electrode plate. An electrical device including a lithium battery having the negative electrode plate.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This disclosure claims priority to and the benefit of Chinese Patent Application No. 202211474567.3, entitled "NEGATIVE ELECTRODE SHEET, LITHIUM BATTERY, AND ELECTRIC DEVICE," filed on November 23, 2022. The entire contents of the above application are incorporated herein by reference.

[0002] The present disclosure relates to the technical field of lithium ion batteries, and in particular to negative electrode plates, lithium batteries, and electrical devices. [Background technology]

[0003] In the related art, lithium-ion batteries generally use graphite as the negative electrode active material. To meet the demand for increasing the energy density of batteries, both the positive and negative electrodes are becoming increasingly thick. However, this results in a decrease in the fast charging performance of the batteries. Summary of the Invention [Problem to be solved by the invention]

[0004] In view of this, the present disclosure provides a negative electrode plate, a lithium battery, and an electrical device to solve the problem that lithium batteries cannot achieve both high energy density and excellent fast charging performance. [Means for solving the problem]

[0005] According to a first aspect, the present disclosure provides a negative electrode plate including a negative electrode current collector, a capacitance supply layer, a fast ion conductor layer, and a conductive bonding layer. The capacitance supply layer is laminated on at least one side of the negative electrode current collector in the thickness direction and includes a first negative electrode active material, a first binder, and a first conductive agent. The fast ion conductor layer is laminated on the side of the capacitance supply layer facing away from the negative electrode current collector. The fast ion conductor layer includes a carbon active material, a lithium superionic conductor, a second binder, and a second conductive agent, and the specific capacity of the first negative electrode active material is greater than the specific capacity of the carbon active material. The conductive bonding layer is disposed between the capacitance supply layer and the fast ion conductor layer.

[0006] The above-described structure of the negative electrode plate makes ideal use of the difference in lithium ion concentration gradient at different locations in the negative electrode plate. The fast-ion conductor layer, with its strong ion conduction capability, is located on the top layer and close to the separator to enhance lithium ion transport throughout the negative electrode plate and reduce the concentration of lithium ions on the surface of the negative electrode during high-current charging, thereby reducing the risk of lithium deposition. The capacity supply layer is located below the fast-ion conductor layer and close to the negative electrode current collector to ensure excellent dynamic performance throughout the negative electrode plate and help enhance fast charging performance. In addition, the capacity supply layer contains a first negative electrode active material with a higher specific capacity than the carbon active material and is the primary capacity supply layer. The presence of the capacity supply layer ensures that the battery maintains a high energy density even when the negative electrode plate is thin. The conductive adhesive layer is located between the two layers to stabilize the connection between the two layers and provide a buffer space for the volume expansion of the negative electrode during charging, thereby improving the battery's cycling performance. Therefore, a unique three-layer coating structure is used for the negative electrode plate to ensure very high specific capacity of the negative electrode and high-speed transport of lithium ions, thereby enhancing fast charging performance and achieving excellent cycle performance.

[0007] According to a second aspect, the present disclosure provides a lithium battery, the lithium battery including a negative electrode plate according to the first aspect of the disclosure.

[0008] By using the above negative electrode plate, the lithium battery achieves high capacity utilization, high energy density, short charging time, and excellent cycle performance.

[0009] According to a third aspect, the present disclosure provides an electrical device comprising a lithium battery according to the second aspect of the disclosure. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of the structure of a negative electrode plate according to one embodiment of the present disclosure. [Figure 2] FIG. 2 is a graph of room temperature fast charge cycle performance of pouch batteries manufactured using the negative electrode plates according to Embodiments 1 to 8 of the present disclosure and pouch batteries manufactured using the negative electrode plates according to Comparative Examples 1 to 4. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, technical solutions in the embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0012] Referring to FIG. 1 , one embodiment of the present disclosure provides a negative electrode plate 100 including a negative electrode current collector 10 and a capacitance supply layer 21, a conductive bonding layer 22, and a fast-ion conductor layer 23, which are stacked in this order on at least one side of the negative electrode current collector 10 in the thickness direction Z. The capacitance supply layer 21 includes a first negative electrode active material, a first binder, and a first conductive agent. The fast-ion conductor layer 23 includes a carbon active material (i.e., a second negative electrode active material), a lithium superionic conductor, a second binder, and a second conductive agent. The specific capacity of the first negative electrode active material is greater than the specific capacity of the carbon active material. Regarding the conductive bonding layer 22, its name clearly indicates that the conductive bonding layer includes a conductive agent and a binder (which may be referred to as a third conductive agent and a third binder, respectively, for clearer explanation). The thickness direction Z of the negative electrode current collector 10 indicates the stacking direction of the capacitance supply layer 21, the conductive bonding layer 22, and the fast ion conductor layer 23, and is parallel to the thickness direction of the negative electrode current collector 10, the capacitance supply layer 21, the conductive bonding layer 22, and the fast ion conductor layer 23.

[0013] The laminated structure of the capacitance supply layer 21, the conductive bonding layer 22, and the fast ion conductor layer 23 forms the negative electrode coating 20 of the negative electrode plate 100. The fast ion conductor layer 23 is the top layer, far from the negative electrode current collector 10, and is close to the separator. During battery charging, the fast ion conductor layer 23 first receives lithium ions desorbed from the positive electrode. Due to the excellent lithium ion transport ability and established fast lithium ion channels of the fast ion conductor layer 23, the lithium ions at the surface of the negative electrode, which have the highest lithium ion concentration, can be conducted away as quickly as possible, reducing the concentration gradient to prevent the lithium ions from being directly reduced to metallic lithium at the surface of the negative electrode when they cannot react quickly with the negative electrode material. This also ensures that lithium is not deposited in the region with the highest lithium ion concentration, especially during high-current fast charging.

[0014] The capacitance supply layer 21, which primarily supplies capacitance, is located at the bottom and closest to the negative electrode current collector 10. The capacitance supply layer 21 contains a first negative electrode active material with a high specific capacity, which allows the battery to achieve high energy density and allows the negative electrode plate 100 to be made thinner, shortening the lithium ion migration path and improving rate performance. In addition, because a first negative electrode active material with a high specific capacity generally results in poor dynamic performance, the first negative electrode active material is placed at the bottom of the current collector, away from the separator, to better optimize the battery's fast charging performance. Furthermore, without a fast ion conductor layer 23 on top, the first negative electrode active material will initially participate in the high-current reaction, resulting in a decrease in the overall dynamic performance of the electrode plate.

[0015] The intermediate conductive adhesive layer 22 functions as a connecting bond between the capacitance supply layer 21 and the fast ion conductor layer 23 to further tighten the bond between the upper and lower layers, preventing cracks at the interface between the upper and lower layers and layer separation during battery cycling. Furthermore, the conductive adhesive layer 22 has a certain flexibility and can also function as a volume buffer, providing some space for the volume expansion of the upper and lower layers containing active materials during charging and compensating for the volume contraction of the upper and lower layers containing active materials during discharging. The conductive adhesive layer 22, with its certain elasticity, provides a buffering effect against the volume expansion of the first negative electrode active material during charging and discharging, particularly when the first negative electrode active material contained in the capacitance supply layer 21 undergoes significant volume changes during charging and discharging. This reduces the volume change rate of the negative electrode plate 100 during charging and discharging cycles, thereby improving the cycle performance of the battery.

[0016] Therefore, the negative electrode coating in the negative electrode plate 100 has a unique three-layer structure, which ensures a very high specific capacity of the negative electrode, enhances the fast charging performance of the battery, and achieves excellent cycle performance of the battery.

[0017] The term "specific capacity" as used herein refers to mass-specific capacity, i.e., the amount of electricity that can be released from a battery or active material per unit mass. Additionally, "specific capacity" specifically refers to the theoretical specific capacity of a first negative electrode active material being greater than the theoretical specific capacity of a carbon active material, or the actual specific capacity of a first negative electrode active material being greater than the actual specific capacity of a carbon active material. Theoretical specific capacity refers to the amount of charge released or absorbed per unit mass by an active material (e.g., a negative electrode material or a positive electrode material) in a battery under fully reacted conditions. Theoretical specific capacity is calculated based on the stoichiometry of the chemical reaction, assuming that all active materials are involved in the chemical reaction and without considering losses and limitations in the actual battery structure or operating process. Actual specific capacity refers to the actual amount of electricity that a battery or active material can deliver under specific discharge conditions.

[0018] In one embodiment of the present disclosure, the thickness ratio of the fast ion conductor layer 23, the conductive bonding layer 22, and the capacitance supply layer 21 in the thickness direction Z of the negative electrode current collector 10 is (3-5):1:(4-6). Specifically, the thickness ratio can be 3:1:6, 4:1:5, 5:1:4, 3:1:4, 4:1:4, etc. The conductive bonding layer 22 is the thinnest, and therefore can provide a conductive connection function without adversely affecting the total capacity of the entire negative electrode plate 100 or the energy density of the battery core due to a lack of electrochemical activity of the conductive bonding layer 22. In addition, the thickness of the conductive bonding layer 22 is not significantly different from the thicknesses of the capacitance supply layer 21, the fast ion conductor layer 23, etc., thereby ensuring that the conductive bonding layer can actually exert a volume buffering effect. The thicknesses of the capacitance supply layer 21 and the fast ion conductor layer 23 can be freely adjusted as needed, and can be particularly adjusted based on the required total capacity of the negative electrode and the amount of the first negative electrode active material having a high specific capacity added.

[0019] In some embodiments of the present disclosure, the thickness of capacitance layer 21 is equal to or greater than the thickness of fast ion conductor layer 23. In this way, a high energy density of the battery is better ensured.

[0020] In one embodiment of the present disclosure, the sum of the thicknesses of the capacitance supply layer 21, the conductive bonding layer 22, and the fast ion conductor layer 23 on one side of the negative electrode current collector 10 is in the range of 60 μm to 100 μm. In other words, the thickness of the negative electrode coating 20 on one side is in the range of 60 μm to 100 μm. Having an appropriate thickness for the negative electrode coating 20 not only ensures ease of implementation of the coating process, but also prevents the adverse effects of excessive thickness on the battery's fast charging performance. Specifically, the sum of the thicknesses can be 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, etc.

[0021] In some embodiments, the thickness of the conductive bonding layer 22 can be in the range of 6 μm to 10 μm, such as 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.3 μm, 9 μm, 9.5 μm, or 10 μm, and optionally in the range of 6 μm to 8 μm. The thickness of the capacitance supply layer 21 can be in the range of 24 μm to 60 μm, such as 24 μm, 25 μm, 30 μm, 32 μm, 35 μm, 40 μm, 42 μm, 50 μm, 55 μm, or 60 μm. The thickness of the fast ion conductor layer 23 can be in the range of 18 μm to 50 μm, for example, 18 μm, 20 μm, 24 μm, 25 μm, 28 μm, 30 μm, 35 μm, 40 μm, 45 μm, 48 μm, or 50 μm, and optionally in the range of 18 μm to 30 μm.

[0022] In the present disclosure, although the capacity supply layer 21 is the main capacity source of the battery, the fast ion conductor layer 23 also contributes to capacity. In one embodiment of the present disclosure, the fast ion conductor layer 23 contains the following components in mass percent: 70 wt% to 89 wt% carbon active material, 4 wt% to 10 wt% lithium superionic conductor, 5 wt% to 10 wt% second binder, and 6 wt% to 10 wt% second conductive agent. In this way, the fast ion conductor layer 23 not only enhances lithium ion transport capability but also contributes to capacity to some extent, ensuring that the coating does not easily peel off. Specifically, the mass percent content of the carbon active material in the fast ion conductor layer 23 can be 70%, 75%, 80%, 82%, 85%, 88%, 89%, etc. The content of the lithium superionic conductor in the fast ion conductor layer 23, in weight percent, can be 4%, 5%, 6%, 7%, 8%, 9%, 9.5%, 10%, etc. The content of the second binder in the fast ion conductor layer 23, in weight percent, can be 5%, 5.5%, 6%, 7%, 8%, 9%, 9.5%, 10%, etc. The content of the second conductive agent in the fast ion conductor layer 23, in weight percent, can be 6%, 7%, 8%, 9%, 9.5%, 10%, etc. In some embodiments, the mass ratio of the carbon active material, the lithium superionic conductor, the first binder, and the first conductive agent in the capacitance supply layer 21 is 8:0.5:0.5:1, 7:1:1:1, etc.

[0023] Lithium superionic conductors include Li3SBF4, LiAlSiO4, LiTaSiO5, and Li 10 SiPO 10 , Li2P3SiO8, and the like. These lithium superionic conductor materials have high ionic conductivity, which can enhance the ability of the negative electrode plate 100 to transport lithium ions.

[0024] The carbon active material may include one or more of hard carbon, soft carbon, graphite (e.g., artificial graphite and natural graphite), mesophase carbon microbeads, etc. The second conductive agent may include one or more of carbon nanotubes, graphene, carbon fiber, carbon black (e.g., acetylene black, Ketjen black, Supper P, or 350G carbon black), etc. The carbon nanotubes may be single-walled or multi-walled carbon nanotubes, and the carbon fiber may be aligned carbon fibers. Although both the carbon active material and the first conductive agent are carbon materials herein, it should be noted that the conductive ability of the conductive agent is significantly superior to that of the carbon active material, and the lithium intercalation ability is negligible. However, the carbon active material has excellent lithium intercalation ability and can be used as a negative electrode active material.

[0025] The second binder may be selected from one or more of, but not limited to, styrene-butadiene rubber (SBR), polyacrylate, polyacrylonitrile (PAN), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyimide (PI) or variants thereof, sodium carboxymethylcellulose (CMC), sodium alginate, and the like.

[0026] In an embodiment of the present disclosure, the conductive bonding layer 22 includes the following components in weight percent: 10 wt% to 30 wt% of a third binder and 70 wt% to 90 wt% of a third conductive agent. This ensures that the conductive bonding layer 22 has good adhesive and conductive properties and can provide a good elastic connection between the capacitance supply layer 21 and the fast ion conductor layer 23. The weight ratio of the third conductive agent to the third binder ranges from 2.33 to 9. Specifically, the content of the third binder in the conductive bonding layer 22 in weight percent can be 10%, 12%, 15%, 20%, 22%, 25%, 28%, 30%, etc. The content of the third conductive agent in the conductive bonding layer 22 in weight percent can be 70%, 72%, 75%, 80%, 82%, 85%, 88%, 90%, etc.

[0027] In one embodiment of the present disclosure, the capacitance supply layer 21 includes the following components in mass percent: 60 wt% to 80 wt% of a first negative electrode active material, 10 wt% to 30 wt% of a first binder, and 1 wt% to 15 wt% of a first conductive agent. Specifically, the mass percent content of the first negative electrode active material in the capacitance supply layer 21 may be 60%, 62%, 65%, 70%, 75%, 78%, 80%, etc. The mass percent content of the first binder in the capacitance supply layer 21 may be 10%, 11%, 15%, 20%, 22%, 25%, 28%, 30%, etc. The mass percent content of the first conductive agent in the capacitance supply layer 21 may be 1%, 2%, 3%, 5%, 8%, 10%, 12%, 14%, 15%, etc. In some embodiments, the weight ratio of the first negative electrode active material, the first binder, and the first conductive agent is 6:3:1, 7:2:1, 8:1:1, or the like.

[0028] In some embodiments of the present disclosure, the weight percent of the first binder in the capacitance layer 21 is greater than the weight percent of the second binder in the fast ion conductor layer 23. This ensures strong adhesion between the capacitance layer 21 and the anode current collector 10, so that the capacitance layer 21 will not peel off from the surface of the anode current collector 10 even if other coatings peel off when the battery is subjected to abuse such as compression, impact, or puncture, thereby avoiding direct contact between the anode current collector 10 and the cathode and reducing the risk of thermal runaway in the battery core.

[0029] For the selection range of the third binder and the first binder, please refer to the above description of the second binder in this disclosure. For the selection range of the third conductive agent and the first conductive agent, please refer to the above description of the second conductive agent in this disclosure. Details will not be described again in this specification. It can be understood that the third binder or the first binder and the second binder may have the same or different materials, and that the third conductive agent or the first conductive agent and the second conductive agent may have the same or different materials.

[0030] In the present disclosure, the specific capacity of the first negative electrode active material is greater than the specific capacity of the carbon active material, and the first negative electrode active material can be selected from one or more of silicon-based materials, tin-based materials, phosphorus-based materials, etc. In one embodiment of the present disclosure, the first negative electrode active material is a silicon-based material. Silicon-based materials are widely available, inexpensive, and have a much higher specific capacity than carbon active materials. The use of silicon-based materials in the negative electrode of a battery can increase the energy density of the battery and reduce the thickness of the electrode plate. Specifically, the silicon-based material can include one or more of elemental silicon, silicon alloys, silicon oxides, and silicon-carbon composite materials. The silicon-carbon composite material can include a silicon-containing material (e.g., elemental silicon, silicon alloys, or silicon oxides) and a carbon material. The silicon-containing material and the carbon material can be combined in a coated form (e.g., a carbon material-coated silicon-containing material) and / or a dispersed form. In some embodiments, the first negative electrode active material is a silicon-carbon composite material.Compared with other silicon-based materials, the silicon-carbon composite material has excellent electrical conductivity, dynamic performance, and cycle performance.Furthermore, in some embodiments, the silicon-carbon composite material contains silicon particles, and the size of the silicon particles is 5 nm or less.In this case, the silicon-carbon composite material exhibits low volume expansion effect and excellent dynamic performance.The size of the silicon particles specifically refers to the diameter of the silicon particles.

[0031] In some embodiments of the present disclosure, a coating layer is further provided on the surface of the first negative electrode active material. The presence of the coating layer can provide a buffering function for the volume expansion of the first negative electrode active material during lithium desorption and can also isolate the electrolyte from direct contact with the first negative electrode active material, thereby reducing the occurrence of side reactions. If the coating layer is made of a conductive material, it can further increase the conductivity of the first negative electrode active material.

[0032] The coating layer typically comprises a conductive material that does not react with the electrolyte. Examples of the coating layer include, but are not limited to, one or more of graphene, polyaniline, polypyrrole, polydopamine, and the like. In one embodiment of the present disclosure, the thickness of the coating layer ranges from 50 nm to 150 nm. A coating layer of an appropriate thickness does not easily crack during battery cycling and does not significantly reduce the specific capacity of the entire material (i.e., the first negative electrode active material having the coating layer).

[0033] In the present disclosure, the negative electrode current collector 10 can include, but is not limited to, copper foil, copper alloy foil, a film material coated with metallic copper, the above material with a carbon-coated surface, etc. The metallic copper can be elemental copper or a copper alloy.

[0034] The negative plate provided in this embodiment of the present disclosure can be made by using the following method: In this order, a first paste containing a first negative electrode active material, a first binder, and a first conductive agent is applied to at least one side of a negative electrode current collector 10 and dried to form a capacity supply layer 21; a second paste containing a third binder and a third conductive agent is applied and dried to form a conductive bonding layer 22; a third negative electrode paste containing a carbon active material, a lithium superionic conductor, a second binder, and a second conductive agent is applied and dried to form a fast ion conductor layer 23; and pressing is performed to obtain a negative electrode plate, wherein the specific capacity of the first negative electrode active material is greater than the specific capacity of the carbon active material.

[0035] The solvents contained in the first paste, the second paste, and the third paste may be the same or different and may be independently selected from one or more of water, alcohol solvents (e.g., ethanol), N-methylpyrrolidone (NMP), dimethylformamide (DMF), diethylformamide (DEF), etc. The content of the solvent is not particularly limited as long as the solvent can meet the fluidity and uniformity required for paste application. The paste can be applied by one or a combination of several methods, including spin coating, brush coating, spray coating, dip coating, and blade coating. The pressing method can be roll pressing.

[0036] The negative electrode current collector 10 can be coated on one or both sides. In other words, the stacked structure of the capacitance supply layer 21, the conductive bonding layer 22, and the fast ion conductor layer 23 can be formed on one side of the negative electrode current collector 10, or the stacked structure of the capacitance supply layer 21, the conductive bonding layer 22, and the fast ion conductor layer 23 can be formed on each of two opposing side surfaces of the negative electrode current collector 10.

[0037] In addition, the second paste can be applied directly onto the first paste or onto the capacitance supply layer 21 formed by drying the first paste. The third paste is applied in a similar manner. In some embodiments, the first paste, second paste, and third paste are applied sequentially to one side of the negative electrode current collector 10 and then dried together. If double-sided coating is required, the above process can be repeated on the other side of the negative electrode current collector 10. In some other embodiments, the first paste can be applied to one side of the negative electrode current collector 10 and dried to form the capacitance supply layer 21, then the second paste can be applied to the capacitance supply layer 21 and dried to form the conductive bonding layer 22, and the third paste can be applied to the conductive bonding layer 22 and dried to form the fast ion conductor layer 23. If double-sided coating is required, the above process can be repeated on the other side of the negative electrode current collector 10.

[0038] The method for fabricating the negative electrode plate is simple, and the fabricated negative electrode plate has a novel stable structure and can achieve both high energy density and excellent fast charging performance.

[0039] An embodiment of the present disclosure further provides a lithium battery, the lithium battery including a negative electrode plate according to an embodiment of the present disclosure.

[0040] In one embodiment of the present disclosure, the lithium battery further includes a positive electrode plate and a separator disposed between the negative electrode plate and the positive electrode plate.

[0041] A positive electrode plate typically includes a positive electrode current collector and a positive electrode coating disposed on at least one side of the positive electrode current collector. The positive electrode coating typically contains a positive electrode active material, a conductive agent, and a binder. The positive electrode active material may include, but is not limited to, one or more of the following: a mono-oxide of lithium (e.g., lithium cobalt oxide, lithium manganese oxide, or lithium nickel oxide), a binary oxide of lithium (e.g., lithium nickel manganese oxide or lithium nickel cobalt oxide), a ternary oxide of lithium (e.g., lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide), a multi-element oxide of lithium, a lithium-rich manganese-based material, a lithium-containing phosphate (e.g., lithium iron phosphate or lithium iron manganese phosphate), etc. These positive electrode active materials may be undoped or doped and modified, and may or may not have a coating layer formed on the surface of the positive electrode active material. Generally, a coating layer is typically formed on a phosphate-based active material.

[0042] The separator is configured to separate the positive plate from the negative plate to ensure insulation and liquid retention between the positive and negative plates. The separator, positive plate, and negative plate together form a battery core. The battery core is housed in a battery case and is permeated with an electrolyte solution housed in the case. In some embodiments of the present disclosure, a lithium battery can be assembled using the following method: stacking the positive plate, separator, and negative plate in order to form a battery core, placing the battery core in the battery case, filling the battery case with electrolyte, and then sealing the battery case to obtain a battery. The battery core may be in a wound or stacked form.

[0043] The separator can be any separator material used in batteries. For example, the separator can include, but is not limited to, polymer separators such as a monolayer polypropylene (PP) film, a monolayer polyethylene (PE) film, a bilayer PP / PE film, a bilayer PP / PP film, or a trilayer PP / PE / PP film, a nonwoven fabric, etc. The electrolyte includes an electrolyte salt and an organic solvent. The specific types and compositions of the electrolyte salt and the organic solvent are both common choices in the battery field and can be selected according to actual requirements.

[0044] An embodiment of the present disclosure further provides an electric device, which is equipped with the lithium battery according to the embodiment of the present disclosure. The electric device can be an electric vehicle (e.g., an automobile, a motorcycle, or a bicycle), an electric toy, a 3C product (e.g., a mobile phone, a notebook computer, a tablet computer, a pen-input computer, an e-book player, or a wearable device), etc. By using the battery, the electric device has a long battery life and a fast charging speed.

[0045] The technical solutions of the present disclosure are further described below with reference to several specific embodiments.

[0046] (Embodiment 1) A method for making a negative plate is provided, comprising the following steps:

[0047] (1) A first paste used to form a capacitance supply layer was prepared. The first paste contained water, a first negative electrode active material (specifically, a silicon-carbon composite having a surface with a polypyrrole coating layer approximately 70 nm thick (a silicon-carbon composite core in which porous amorphous carbon and silicon were uniformly distributed, the silicon may be inserted into the pores of the porous amorphous carbon, and the outer layer was coated with polypyrrole), the silicon particles in the core being less than 5 nm in size), a binder (specifically, a modified polyacrylate with product number BA-290S3 purchased from Fujian Blue Ocean & Black Stone New Materials Technology Co., Ltd.), and a conductive agent (specifically, single-walled carbon nanotubes) in a mass ratio of 6:3:1.

[0048] A second paste used to form the conductive adhesive layer was prepared, which contained water, a conductive agent (particularly, graphene), and a binder (particularly, the modified polyacrylate) in a mass ratio of 7:3.

[0049] A third paste used to form the fast-ion conductor layer was prepared, which included water, a carbon active material (particularly hard carbon), a lithium superionic conductor Li3SBF4, a binder (particularly sodium carboxymethyl cellulose and styrene butadiene rubber), and a conductive agent (particularly carbon black) in a mass ratio of 8:0.5:0.5:1.

[0050] (2) Copper foil was used as a negative electrode current collector. A first paste was applied to one side of the copper foil and dried to form a capacitance supply layer, a second paste was applied to one side and dried to form a conductive adhesive layer, and a third paste was applied to one side and dried to form a fast-ion conductor layer. Then, similarly, a stacked capacitance supply layer, conductive adhesive layer, and fast-ion conductor layer were formed on the other side of the copper foil to obtain a double-sided electrode plate. Finally, the double-sided electrode plate was roll-pressed to obtain a negative electrode plate for further use. The thickness ratio of the fast-ion conductor layer, conductive adhesive layer, and capacitance supply layer on both sides of the negative electrode plate was 3:1:6, and the total thickness was 60 μm.

[0051] The manufacturing of a lithium battery is as follows.

[0052] (1) The positive electrode active material, i.e., lithium nickel cobalt manganese oxide, binder (e.g., polyvinylidene fluoride (PVDF)), and conductive agent (e.g., carbon nanotubes) were mixed in a mass ratio of 100:1.2:1 in N-methylpyrrolidone (NMP) as a solvent and thoroughly stirred to obtain a positive electrode paste. The positive electrode paste was applied to aluminum foil, which served as a positive electrode current collector, and then fired, roll-pressed, and cut to obtain a positive electrode plate.

[0053] (2) Battery assembly: In an argon-filled glove box, the negative electrode plate, separator, and positive electrode plate were stacked in order to form a Z-stack battery core. The battery core was filled with electrolyte and sealed with an aluminum-plastic film. After fabrication, capacity grading, and vacuum sealing, a pouch battery was fabricated.

[0054] In addition, it should be noted that the pouch battery used later in the present disclosure to test the fast charging capability of the battery particularly has a three-electrode type, and the method for fabricating the pouch battery includes the following: after obtaining the above Z-stacked battery core, a copper wire is used as a reference electrode, i.e., a third electrode, in the center of the battery core; after manufacturing the pouch battery by using the above method, the copper wire is lithium-plated, and a three-electrode battery is obtained using the lithium-plated copper wire as a reference electrode.

[0055] (Embodiment 2) A negative electrode plate is provided, which differs from the negative electrode plate of embodiment 1 in that the thickness ratio of the fast ion conductor layer, the conductive bonding layer, and the capacitance supply layer is 4:1:5, the mass ratio of graphene to modified polyacrylate in the conductive bonding layer is 9:1, and in the capacitance supply layer, the first negative electrode active material is particularly a silicon-carbon composite material having a surface with a 60 nm thick polypyrrole coating layer, and the mass ratio of the first negative electrode active material, binder, and conductive agent is 8:1:1.

[0056] According to the method described in embodiment 1, the negative electrode plate in embodiment 2 is assembled into a pouch battery.

[0057] (Embodiment 3) A negative electrode plate is provided, which differs from the negative electrode plate of embodiment 1 in that the thickness ratio of the fast ion conductor layer, the conductive bonding layer, and the capacitance supply layer is 5:1:4, the mass ratio of the hard carbon, Li3SBF4, binder, and conductive agent in the fast ion conductor layer is 7:1:1:1, and the mass ratio of the first negative electrode active material, the binder, and conductive agent in the capacitance supply layer is 7:2:1.

[0058] According to the method described in embodiment 1, the negative electrode plate in embodiment 3 is assembled into a pouch battery.

[0059] (Embodiment 4) A negative electrode plate is provided, which differs from the negative electrode plate of embodiment 1 in that the thickness ratio of the fast ion conductor layer, the conductive bonding layer, and the capacitance supply layer is 3:1:4, and the sum of the thicknesses of the fast ion conductor layer, the conductive bonding layer, and the capacitance supply layer on one side of the negative electrode current collector is 80 μm.

[0060] According to the method described in embodiment 1, the negative electrode plate in embodiment 4 is assembled into a pouch battery.

[0061] (Embodiment 5) A negative electrode plate is provided, which differs from the negative electrode plate in embodiment 1 in that on one side of the negative electrode current collector, the total thickness of the fast ion conductor layer, the conductive bonding layer, and the capacitance supply layer is 100 μm, and the thickness ratio of the fast ion conductor layer, the conductive bonding layer, and the capacitance supply layer is still 3:1:6.

[0062] (Embodiment 6) A negative electrode plate is provided, which differs from the negative electrode plate in embodiment 1 in that on one side of the negative electrode current collector, the sum of the thickness of the fast ion conductor layer, the thickness of the conductive bonding layer, and the thickness of the capacitance supply layer is 120 μm, and the thickness ratio of the fast ion conductor layer, the conductive bonding layer, and the capacitance supply layer is still 3:1:6.

[0063] According to the method described in embodiment 1, the negative electrode plate in embodiment 6 is assembled into a pouch battery.

[0064] (Embodiment 7) A negative electrode plate is provided, which differs from the negative electrode plate in embodiment 1 in that the thickness ratio of the fast ion conductor layer, the conductive bonding layer, and the capacitance supply layer on one side of the negative electrode current collector is 2:1:7, while the sum of the thicknesses of the fast ion conductor layer, the conductive bonding layer, and the capacitance supply layer is still 60 μm.

[0065] According to the method described in embodiment 1, the negative electrode plate in embodiment 7 is assembled into a pouch battery.

[0066] (Embodiment 8) A negative electrode plate is provided, and the negative electrode plate differs from the negative electrode plate in embodiment 1 in that no coating layer is provided on the surface of the silicon-carbon composite material in the capacity supply layer.

[0067] According to the method described in embodiment 1, the negative electrode plate in embodiment 8 is assembled into a pouch battery.

[0068] To highlight the beneficial effects of the present disclosure, the following Comparative Examples 1 to 4 are further provided in the present disclosure.

[0069] (Comparative Example 1) A negative electrode plate is provided, which differs from the negative electrode plate in Example 1 in that only one single-layer negative electrode coating is formed on one side of the copper foil, and the negative electrode coating contains only negative electrode active materials, i.e., artificial graphite, a binder, and a conductive agent, in a mass ratio of 8:1:1. The thickness of the negative electrode plate in Comparative Example 1 is 60 μm.

[0070] According to the method described in the first embodiment, the negative electrode plate in the first comparative example is assembled into a pouch battery.

[0071] (Comparative Example 2) A negative electrode plate is provided, and the negative electrode plate differs from the negative electrode plate in embodiment 1 in that only one single-layer negative electrode coating is formed on one side of the copper foil, and the composition of the negative electrode coating is the same as the composition of the capacity supply layer in embodiment 1. The thickness of the negative electrode plate in comparative example 2 is 60 μm.

[0072] According to the method described in the first embodiment, the negative electrode plate in the second comparative example is assembled into a pouch battery.

[0073] (Comparative Example 3) A negative electrode plate is provided, which differs from the negative electrode plate in embodiment 1 mainly in that only one single-layer negative electrode coating is formed on one side of the copper foil, and the composition of the negative electrode coating is the same as the composition of the fast ion conductor layer in embodiment 1. In addition, the thickness of the negative electrode plate in comparative example 3 is 60 μm.

[0074] Comparative Example 4 A negative electrode plate is provided, and the negative electrode plate differs from the negative electrode plate of embodiment 1 mainly in that a conductive adhesive layer is not disposed between the capacitance supply layer and the fast ion conductor layer. In one aspect of the negative electrode plate of comparative example 4, the thickness ratio of the fast ion conductor layer to the capacitance supply layer is 3:7, and the total thickness of the fast ion conductor layer and the capacitance supply layer is 60 μm.

[0075] In order to strongly support the beneficial effects brought about by the technical solutions of the present disclosure, the following performance tests were carried out on the pouch batteries in the above embodiments or comparative examples, respectively.

[0076] a. Fast charging capability test at room temperature: (1) At room temperature (e.g., 25°C), the three-electrode batteries in the embodiments or comparative examples were individually connected to a test cabinet manufactured by LAND Electronic Co., Ltd., and a three-channel Agilent data collector was used to separately collect the voltages between the positive and negative electrodes, between the positive and third electrodes, and between the negative and third electrodes. (2) The battery was charged at a constant current of 0.5 C to an upper voltage limit of 4.2 V, then allowed to stand for 1 hour, discharged at a constant current of 1 / 3 C to a lower voltage limit, and then allowed to stand for 1 hour. (3) The battery was charged at a constant current of 1 C to an upper limit voltage of 4.2 V, then allowed to stand for 1 hour, discharged at a constant current of 1 / 3 C to a lower limit voltage, and then allowed to stand for 1 hour. (4) The battery was charged at a constant current of 1.5 C to an upper limit voltage of 4.2 V, then allowed to stand for 1 hour, discharged at a constant current of 1 / 3 C to a lower limit voltage, and then allowed to stand for 1 hour. (5) The battery was charged at a constant current of 2C to an upper limit voltage of 4.2V, then allowed to stand for 1 hour, discharged at a constant current of 1 / 3C to a lower limit voltage, and then allowed to stand for 1 hour. (6) The battery was charged at a constant current of 3C to an upper limit voltage of 4.2V, then allowed to stand for 1 hour, discharged at a constant current of 1 / 3C to a lower limit voltage, and then allowed to stand for 1 hour. (7) The SOC of the battery was obtained when the potential of the negative electrode relative to the third electrode reached 0 mV at each charge rate, and the charging time required for the negative electrode plate at each charge rate was calculated. The charging times were accumulated to obtain the total charging time required for the SOC to increase from 10% to 80%.

[0077] b. Fast charging capability test at low temperature of -10℃:

[0078] After the same test process as the rapid charge capacity test at room temperature, the test was carried out in a temperature box at -10°C with a rate of 2C and maximum charging current.

[0079] c. Rapid charge cycle test at room temperature (25°C): Each pouch battery (without a reference electrode) in the embodiment or comparative example was subjected to a charge-discharge cycle test at 25°C. The voltage range was 2.75 V to 4.2 V. The cycle strategy was as follows: sequential charging, i.e., first charging to 3.8 V at 3 C, then charging to 4.0 V at 2 C, then charging to 4.1 V at 1 C, and finally charging to 4.2 V at 0.5 C, and discharging to 2.75 V at 1 C. The charge-discharge process was repeated for a specific number of cycles, and the cycle curve of each battery was recorded. The capacity retention rate of each battery after 700 cycles was calculated.

[0080] d. Battery energy density test: The formula for calculating battery energy density is as follows: Battery energy density = Battery capacity (C0) * Average discharge voltage (V) / Battery mass (M).

[0081] The test method for battery capacity (C0) and discharge average voltage (V) was as follows: the battery was charged at 25°C with a cutoff current of 0.05C at a constant current and a constant voltage of 0.33C to 4.2V, allowed to stand for 10 minutes, and discharged at 0.33C to 2.5V, with the discharge capacity recorded as C0 and the discharge average voltage recorded as V. The relevant test results are summarized in Table 1 below. A graph of the fast charge cycle performance of the pouch batteries in some examples is shown in Figure 2.

[0082] [Table 1]

[0083] Table 1 shows that, compared to Comparative Example 1, in which only graphite is used in the anode and no layer coating is applied, the batteries according to Embodiments 1 to 8 of the present disclosure exhibit significantly improved fast charge capacity, cycling performance, energy density, etc.; and compared to Comparative Example 2, in which a single-layer anode coating using a silicon-carbon composite material is used as the anode active material, the batteries according to Embodiments 1 to 8 of the present disclosure exhibit significantly improved fast charge capacity and cycling performance without causing a significant decrease in the battery's energy density. The batteries according to Embodiments 1 to 8 of the present disclosure also exhibit higher energy densities than Comparative Example 3, in which only a single-layer anode coating having the same formulation as the fast-ion conductor layer according to the present disclosure is used. Additionally, compared to Embodiment 1, the battery according to Comparative Example 4, which does not have a conductive adhesive layer, exhibits higher capacity retention after 700 cycles. However, at approximately the 900th cycle, the battery's capacity retention begins to drop sharply. This is likely due to the absence of the conductive adhesive layer. Without this layer, the interface between the capacitance supply layer and the fast-ion conductor layer would crack as cycling progresses. These cracks lead to bond failure and block the paths of ions and electrons.

[0084] In another respect, a comparison of Embodiments 1 and 5 with Embodiment 6 reveals that when the sum of the thicknesses of the fast ion conductor layer, the conductive bonding layer, and the capacitance supply layer is within the preferred range of 60 μm to 100 μm, the battery exhibits excellent fast charging capability and high cycling performance. A comparison of Embodiments 1 and 7 reveals that when the thickness ratio of the fast ion conductor layer, the conductive bonding layer, and the capacitance supply layer is within the preferred range of (3-5):1:(4-6), the battery exhibits excellent fast charging capability and high cycling performance, and the long-term cycling curve is less likely to exhibit a "sharp drop." A comparison of Embodiments 1 and 8 reveals that when a conductive coating layer of an appropriate thickness is provided on the surface of the silicon-carbon composite material in the capacitance supply layer of the battery, the battery exhibits better cycling performance.

[0085] The above embodiments only show some implementations of the present disclosure. Although the description of the embodiments has been described in detail and specifically, it should not be construed as a limitation on the patent scope of the present disclosure. Those skilled in the art can make some modifications and improvements without departing from the concept of the present disclosure. These modifications and improvements shall fall within the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure shall be subject to the appended claims.

Claims

1. A negative electrode current collector (10), a capacity supply layer (21) laminated on at least one side surface of the negative electrode current collector (10) in the thickness direction (Z), the capacity supply layer including a first negative electrode active material, a first binder, and a first conductive agent; a fast ion conductor layer (23) laminated on a side of the capacity supply layer (21) facing away from the negative electrode current collector (10), the fast ion conductor layer (23) including a carbon active material, a lithium superionic conductor, a second binder, and a second conductive agent, wherein the specific capacity of the first negative electrode active material is greater than the specific capacity of the carbon active material; an electrically conductive bonding layer (22) disposed between the capacitance supply layer (21) and the fast ion conductor layer (23); A negative electrode plate (100).

2. 2. The negative electrode plate (100) according to claim 1, wherein a thickness ratio of the fast ion conductor layer (23), the conductive bonding layer (22), and the capacitance supply layer (21) in the thickness direction (Z) of the negative electrode current collector (10) is (3 to 5):1:(4 to 6).

3. 3. The negative electrode plate (100) of claim 2, wherein the sum of the thickness of the capacitance supply layer (21), the thickness of the conductive bonding layer (22), and the thickness of the fast ion conductor layer (23) on one side of the negative electrode current collector (10) is in the range of 60 μm to 100 μm.

4. 4. The negative electrode plate (100) of claim 2 or 3, wherein the thickness of the capacitance-providing layer (21) is equal to or greater than the thickness of the fast ion conductor layer (23).

5. The fast ion conductor layer (23) comprises the following components in weight percent: 70 wt % to 89 wt % of a carbon active material, 4 wt % to 10 wt % of a lithium superionic conductor, 5 wt % to 10 wt % of a second binder, and 6 wt % to 10 wt % of a second conductive agent; The negative electrode plate (100) of any one of claims 1 to 4, comprising:

6. 6. The negative electrode plate according to claim 1, wherein the conductive bonding layer comprises a third binder having a mass percent of 10 wt % to 30 wt % and a third conductive agent having a mass percent of 70 wt % to 90 wt %.

7. The capacitance supply layer (21) comprises the following components in weight percent: 60 wt % to 80 wt % of the first negative electrode active material, 10 wt % to 30 wt % of the first binder, and 1 wt % to 15 wt % of the first conductive agent; The negative electrode plate (100) of any one of claims 1 to 6, comprising:

8. 8. The negative electrode plate (100) of claim 1, wherein the weight percent of the first binder in the capacitance-providing layer (21) is equal to or greater than the weight percent of the second binder in the fast ion conductor layer (23).

9. 9. The negative electrode plate (100) of claim 1, wherein the carbon active material comprises one or more of hard carbon, soft carbon, graphite, and mesophase carbon microbeads, and the first conductive agent and the second conductive agent are independently selected from one of carbon nanotubes, graphene, carbon fiber, and carbon black.

10. 10. The negative electrode plate (100) of any one of claims 1 to 9, wherein the first negative electrode active material is a silicon-based material, the silicon-based material including one or more of elemental silicon, a silicon alloy, a silicon oxide, and a silicon-carbon composite material.

11. The negative electrode plate (100) of claim 10, wherein a surface of the first negative electrode active material further comprises a coating layer.

12. 12. The negative electrode plate (100) of claim 11, wherein the coating layer comprises one or more of graphene, polyaniline, polypyrrole, and polydopamine.

13. The negative electrode plate (100) according to claim 11 or 12, wherein the thickness of the coating layer is in the range of 50 nm to 150 nm.

14. 12. The negative electrode plate (100) of claim 10 or 11, wherein the first negative electrode active material is a silicon-carbon composite material, the silicon-carbon composite material includes silicon particles, and the size of the silicon particles is 5 nm or less.

15. A lithium battery comprising the negative electrode plate (100) according to any one of claims 1 to 14.

16. An electrical device comprising the lithium battery according to claim 15.

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