An anode sheet, a preparation method thereof, and a battery

Abstract

This invention provides a negative electrode sheet, its preparation method, and a battery. The negative electrode sheet includes a current collector and a first active layer and a second active layer sequentially stacked on at least one side surface of the current collector. The first active layer includes a first active material, a first conductive agent, a first binder, and a metal catalyst. The metal catalyst includes silver nanoparticles with a (111) facet. The second active layer includes a second active material, a solid electrolyte material, a second conductive agent, and a second binder. The negative electrode sheet of this invention fundamentally regulates the deposition behavior of lithium ions by constructing a surface layer for rapid lithium ion transport and a bottom layer with catalytic effects. This reduces the lithium deposition overpotential, allowing lithium ions to preferentially nucleate uniformly at the catalyst sites in the bottom layer, rather than randomly accumulating and forming dendrites on the surface layer. This solves the problem of lithium dendrite growth caused by uneven lithium ion deposition under high-rate charging conditions in lithium-ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and relates to a negative electrode sheet, its preparation method, and a battery. Background Technology

[0002] With the increasing demands for fast charging performance in new energy vehicles and consumer electronics, lithium-ion batteries need to be charged in a shorter time. However, under high-rate charging conditions, lithium plating is very likely to occur on the negative electrode surface of lithium-ion batteries, forming lithium dendrites. The growth of lithium dendrites not only consumes active lithium and leads to capacity decay, but may also puncture the separator, causing internal short circuits and posing serious safety hazards.

[0003] To address the lithium plating problem, existing technologies are mainly improved in the following two directions:

[0004] (1) Physical structure regulation: By optimizing the porosity and tortuosity of the negative electrode coating or adding conductive agents with specific morphologies, faster transport channels for lithium ions can be provided, attempting to delay the occurrence of lithium plating from a kinetic perspective. For example, a high-porosity surface structure can be constructed by using a double-layer coating method.

[0005] (2) Interface film modification: A solid electrolyte interface (SEI) film is formed on the surface of the negative electrode by electrolyte additives (such as fluoroethylene carbonate and vinylene carbonate), which inhibits the nucleation and growth of lithium dendrites by utilizing its physical barrier effect.

[0006] However, the above technical solutions have fundamental limitations. Simply controlling the physical structure is a passive "guidance" and it is difficult to fundamentally change the deposition behavior of lithium ions on the negative electrode surface. Furthermore, the SEI film formed by electrolyte additives is prone to rupture and failure during long-term cycling, especially under the impact of the drastic volume expansion of the silicon negative electrode, resulting in the loss of its protective function.

[0007] Therefore, existing technologies remain at the level of "physical suppression" or "sacrificial protection," and there is an urgent need for a negative electrode that can actively guide lithium ions to achieve uniform and dendrite-free deposition from the electrochemical deposition mechanism. Summary of the Invention

[0008] The purpose of this invention is to provide a negative electrode sheet, its preparation method, and a battery. The negative electrode sheet fundamentally regulates the deposition behavior of lithium ions by constructing a surface layer that rapidly transports lithium ions and a bottom layer with catalytic effects, thereby reducing the lithium deposition overpotential and enabling lithium ions to preferentially and uniformly nucleate at the catalyst sites in the bottom layer, rather than randomly accumulating and forming dendrites on the surface layer. This solves the problem of lithium dendrite growth caused by uneven lithium ion deposition under high-rate charging conditions, which leads to capacity decay and safety risks in lithium-ion batteries.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a negative electrode sheet, the negative electrode sheet comprising a current collector and a coating on at least one side surface of the current collector, the coating comprising a first active layer and a second active layer stacked sequentially, the first active layer being disposed on the surface of the current collector, and the second active layer being disposed on the side surface of the first active layer away from the current collector;

[0011] The first active layer includes a first active material, a first conductive agent, a first binder, and a metal catalyst, wherein the metal catalyst includes silver nanoparticles with a (111) facet as the main crystal plane;

[0012] The second active layer includes a second active material, a solid electrolyte material, a second conductive agent, and a second binder.

[0013] In this invention, the first active layer serves as the bottom layer and contains a metal catalyst. The main crystal plane of the metal catalyst is silver nanoparticles with a specific (111) crystal plane. Utilizing its unique adsorption and reduction catalytic effect on lithium ions, it reduces the lithium deposition overpotential, allowing lithium ions to preferentially nucleate uniformly at the metal catalyst sites in the first active layer, rather than randomly accumulating to form dendrites on the surface. This is fundamentally different from the existing technology that only uses metal particles to improve conductivity or guide physical deposition. This invention utilizes the catalytic activity of metal nanoparticles to induce uniform in-plane deposition of lithium ions at the bottom layer of the negative electrode. Furthermore, the second active layer serves as the top layer and contains a solid electrolyte material, acting as a "highway" to ensure that lithium ions quickly and uniformly pass through the top layer to reach the bottom layer. The bottom layer acts as a "smart parking lot," inducing lithium ions to park (deposit) in an orderly and uniform manner. Therefore, this invention constructs a two-layer structure of a fast ion conductor layer on the surface and a catalytic deposition layer on the bottom layer. The two layers work synergistically to achieve perfect coupling of ion transport and deposition, solving the problem of lithium dendrite growth caused by uneven lithium ion deposition under high-rate charging conditions, which leads to capacity decay and safety risks in lithium-ion batteries.

[0014] It is understood that the metal catalyst described in this invention includes silver nanoparticles with a (111) crystal plane as the main crystal plane. This means that the (111) crystal plane accounts for the largest proportion of the silver nanoparticles and is the main crystal plane. Specifically, in the X-ray diffraction pattern, the intensity of the diffraction peak of the (111) crystal plane accounts for more than 80% of the total intensity of the diffraction peaks of all crystal planes. That is, in the silver nanoparticles with a (111) crystal plane as the main crystal plane, the intensity of the X-ray diffraction peak of the (111) crystal plane accounts for more than 80% of the total intensity of the X-ray diffraction peaks of all crystal planes. For example, it can be 80%, 82%, 84%, 86%, 88% or 90%, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] Preferably, the particle size D50 of the silver nanoparticles with the main crystal plane (111) is 30nm-100nm, for example, it can be 30nm, 50nm, 70nm, 90nm or 100nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0016] Preferably, the method for preparing the silver nanoparticles with (111) crystal planes includes the following steps:

[0017] The silver source, crystal plane guide agent, reducing agent and solvent (such as deionized water) are mixed and reacted. After the reaction is completed, solid-liquid separation is performed to obtain silver nanoparticles with (111) crystal plane.

[0018] Preferably, the silver source includes silver nitrate, the reducing agent includes ascorbic acid, and the crystal plane guiding agent includes citric acid.

[0019] Preferably, the reaction temperature is 60℃-90℃, for example, 60℃, 70℃, 80℃ or 90℃, and the time is 1.5h-3h, for example, 1.5h, 2h, 2.5h or 3h, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] If the reaction time is too short, the reaction will be incomplete and the crystal planes will not be sufficiently guided; however, if the reaction time is too long, it may lead to the agglomeration and growth of particles.

[0021] Preferably, the mass ratio of the silver source, crystal plane guide agent and reducing agent is 1:(0.5-2):(0.8-1.5), for example, it can be 1:0.5:0.8, 1:1:1, 1:1.5:1.3 or 1:2:1.5, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 1:1:1.2.

[0022] Preferably, in the first active layer, based on 100 parts by mass of the first active material, the number of parts of the metal catalyst is 0.05-0.5 parts, for example, it can be 0.05 parts, 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts or 0.5 parts, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] In the first active layer of this invention, the amount of metal catalyst affects its performance. If the amount added is too small, the uniformity of lithium ion deposition in the surface will decrease. However, if too much is added, the following problems will arise: 1) Silver nanoparticles themselves do not have lithium storage capacity. Adding too much will dilute the proportion of active material, resulting in a decrease in the overall specific capacity of the electrode and a reduction in energy density; 2) Too much silver nanoparticles may agglomerate or electrochemically dissolve and deposit during cycling, which will damage the stability of the electrode structure; 3) Metallic silver has excellent conductivity. Excessive addition may lead to local current density concentration, which may induce uneven lithium deposition and increase the risk of micro-short circuits.

[0024] Preferably, in the first active layer, based on 100 parts by mass of the first active material, the number of parts of the first conductive agent is 1 to 3 parts, for example, it can be 1 part, 1.5 parts, 2 parts, 2.5 parts or 3 parts, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] Preferably, in the first active layer, based on 100 parts by mass of the first active material, the number of parts of the first adhesive is 1 to 3 parts, for example, it can be 1 part, 1.5 parts, 2 parts, 2.5 parts or 3 parts, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] Preferably, the first active material includes a capacity-type negative electrode active material, which includes a capacity-type graphite material and / or a silicon-carbon composite material.

[0027] Preferably, the first conductive agent comprises any one or a combination of at least two of carbon black, carbon nanotubes, or graphene.

[0028] Preferably, the first adhesive comprises any one or a combination of at least two of styrene-butadiene rubber, sodium carboxymethyl cellulose, or polyacrylic acid.

[0029] Preferably, in the second active layer, based on 100 parts by mass of the second active material, the number of parts of the solid electrolyte material is 2 to 5 parts, for example, 2, 3, 4 or 5 parts, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] In the second active layer of this invention, the amount of solid electrolyte material affects the lithium-ion transport effect. If the amount of solid electrolyte material is too small, the lithium-ion transport rate will decrease, which will not only affect the fast charging performance, but also the uniformity of lithium-ion deposition. However, if too much solid electrolyte material is added, the following problems will occur: 1) Solid electrolytes (such as LATP) have extremely poor electronic conductivity. Adding too much will significantly increase the electronic resistance of the second active layer, leading to increased ohmic polarization of the electrode, increased heat generation during charging, and a decrease in rate performance; 2) Solid electrolyte particles have high rigidity and poor adhesion. Adding too much will lead to a decrease in coating flexibility, making it easy for powder to fall off and crack during rolling and winding, affecting production yield and cell safety.

[0031] Preferably, in the second active layer, based on 100 parts by mass of the second active material, the number of parts of the second conductive agent is 1 to 2 parts, for example, it can be 1 part, 1.25 parts, 1.5 parts, 1.75 parts or 2 parts, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, in the second active layer, based on 100 parts by mass of the second active material, the number of parts of the second adhesive is 1 to 3 parts, for example, it can be 1 part, 1.5 parts, 2 parts, 2.5 parts or 3 parts, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, the solid electrolyte material includes any one or a combination of at least two of lithium aluminum titanium phosphate, lithium aluminum germanium phosphate (LAGP), lithium lanthanum zirconium oxide (LLZO), or lithium lanthanum titanium oxide (LLTO).

[0034] Preferably, the particle size D50 of the solid electrolyte material is 50nm-200nm, for example, it can be 50nm, 100nm, 150nm or 200nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] Preferably, the second active material includes a fast-charging negative electrode active material, wherein the fast-charging negative electrode active material includes a fast-charging artificial graphite material.

[0036] In order to match the functions of the first active layer and the second active layer, the first active layer uses a high-capacity negative electrode active material, and the second active layer uses a fast-charging negative electrode active material. This ensures the overall energy density and promotes the rapid passage of lithium ions through the second active layer to the first active layer, so that lithium ions are uniformly deposited in the plane.

[0037] The compacted density of the volumetric graphite material described in this invention is ≥1.65 g / cm³. 3For example, it could be 1.65 g / cm³ 3 1.7g / cm 3 1.75g / cm 3 Or 1.8g / cm 3 The particle size D50 is 12-18 μm, for example, it can be 12 μm, 14 μm, 16 μm or 18 μm, and the specific surface area is ≤1.5 m². 2 / g, for example, could be 1.5m 2 / g, 1.4m 2 / g, 1.3m 2 / g or 1.2m 2 / g, graphitization degree ≥93%, for example, it can be 93%, 94%, 95% or 96%; the compaction density of the fast-charging artificial graphite material of this invention is ≤1.55g / cm³. 3 For example, it could be 1.55 g / cm³ 3 1.53g / cm 3 1.50g / cm 3 Or 1.48g / cm 3 The particle size D50 is 5μm-12μm, for example, it can be 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm or 12μm, and the specific surface area is ≥2.5m². 2 / g, for example, could be 2.5m 2 / g, 2.7m 2 / g, 2.9m 2 / g or 3.1m 2 / g, with a graphitization degree of 90%-93%, such as 90%, 91%, 92% or 93%, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] The capacity-type graphite material described in this invention focuses on high energy density and high compaction characteristics, while the fast-charging artificial graphite material focuses on short solid-phase diffusion paths and highly reactive interfaces. Therefore, the compaction density and specific surface area of ​​the capacity-type graphite material and the fast-charging artificial graphite material are different.

[0039] Preferably, the particle size D50 of the second active material is 5μm-12μm, for example, it can be 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm or 12μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0040] Preferably, the second conductive agent comprises carbon black and / or carbon nanotubes.

[0041] Preferably, the second adhesive comprises styrene-butadiene rubber and / or sodium carboxymethyl cellulose.

[0042] Preferably, the ratio of the thickness of the first active layer to the thickness of the second active layer is (1.5-2.5):1, for example, it can be 1.5:1, 2.0:1 or 2.5:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] Preferably, the thickness of the first active layer is 45μm-65μm, for example, it can be 45μm, 50μm, 55μm, 60μm or 65μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0044] The first active layer of this invention mainly serves the functions of lithium storage and catalytic deposition. If the thickness of the first active layer is too thin, it will not be able to provide sufficient active material capacity, and may cause uneven deposition due to insufficient catalyst sites. However, if the thickness of the first active layer is too thick, the lithium ion transport path from the surface to the bottom layer near the current collector will be too long, which will increase polarization, weaken fast charging performance, and even lead to lithium plating at the bottom.

[0045] Preferably, the thickness of the second active layer is 25μm-35μm, for example, it can be 25μm, 27μm, 29μm, 31μm, 33μm or 35μm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0046] The function of the second active layer in this invention is to conduct ions quickly. If the thickness of the second active layer is too thin, the coverage of the active material of the first active layer may be uneven, resulting in local obstruction of lithium ion transport. However, if the thickness of the second active layer is too thick, it will increase the time for lithium ions to pass through the surface, reduce the rate performance, and squeeze the thickness space of the first active layer, resulting in a decrease in energy density.

[0047] Preferably, the exchange current density of the lithium deposition-dissolution reaction of the negative electrode is i o i o ≥2.5mA / cm 2 For example, it could be 2.5 mA / cm 2 2.7mA / cm 2 2.9mA / cm 2 3.1 mA / cm 2 3.3mA / cm 2 3.5mA / cm 2 3.7mA / cm 2 Or 3.5mA / cm 2 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0048] The negative electrode sheet described in this invention, in lithium / negative electrode half-cell testing, yields the lithium deposition-dissolution reaction exchange current density i obtained by Tafel curve testing. o ≥2.5mA / cm 2 This indicates a significant improvement in the battery's dynamic performance.

[0049] In a second aspect, the present invention provides a method for preparing a negative electrode sheet as described in the first aspect, the method comprising the following steps:

[0050] The first active material, the first conductive agent, the first binder, the metal catalyst and the first solvent (deionized water) are mixed to obtain the first slurry;

[0051] The second active material, the solid electrolyte material, the second conductive agent, the second binder, and the second solvent (deionized water) are mixed to obtain the second slurry;

[0052] The first slurry and the second slurry are sequentially layered and coated (double-layer coating method) on at least one side of the current collector, and the negative electrode sheet is obtained after drying and rolling.

[0053] Thirdly, the present invention provides a battery comprising a negative electrode as described in the second aspect.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] This invention contains a metal catalyst in the first active layer, which is silver nanoparticles with a specific (111) crystal plane as the main crystal. The metal catalyst utilizes its unique adsorption and reduction catalytic effect on lithium ions to reduce the lithium deposition overpotential, so that lithium ions preferentially nucleate uniformly at the metal catalyst sites in the first active layer, rather than randomly accumulating to form dendrites on the surface. The second active layer, which is the surface layer, contains a solid electrolyte material to ensure that lithium ions pass through the surface layer quickly and uniformly to reach the bottom layer, inducing orderly and uniform deposition of lithium ions. Therefore, this invention constructs a two-layer structure of a fast ion conductor layer on the surface and a catalyst deposition layer on the bottom layer. The two layers work together to achieve perfect coupling of ion transport and deposition, solving the problem of lithium dendrite growth caused by uneven lithium ion deposition under high-rate charging conditions, which leads to capacity decay and safety risks in lithium-ion batteries. Detailed Implementation

[0056] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0057] Example 1

[0058] This embodiment provides a negative electrode sheet, which includes a current collector (specifically an 8μm thick copper foil) and a first active layer with a thickness of 55μm and a second active layer with a thickness of 30μm, which are sequentially stacked on one side surface of the current collector.

[0059] In the first active layer, based on a mass fraction of 100 parts of the first active material, the first active layer comprises 100 parts of the first active material (D50 is 16 μm, compaction density is 1.75 g / cm³). 3 Its specific surface area is 1.3 m². 2 / g of capacity-type artificial graphite material with a graphitization degree of 95%, 2 parts of carbon nanotubes, 2 parts of styrene-butadiene rubber, 1.2 parts of sodium carboxymethyl cellulose and 0.1 parts of metal catalyst; the metal catalyst is silver nanoparticles with a particle size D50 of 55nm and a main crystal plane of (111), wherein the X-ray diffraction peak intensity of the (111) crystal plane accounts for 85% of the total intensity of the X-ray diffraction peaks of all crystal planes;

[0060] In the second active layer, based on a mass fraction of 100 parts of the second active material, the second active layer comprises 100 parts of the second active material (particle size D50 of 8 μm and compaction density of 1.53 g / cm³). 3 Its specific surface area is 3.0 m². 2 / g of fast-charging artificial graphite material with a graphitization degree of 91%, 3 parts of lithium titanium aluminum phosphate (particle size D50 of 100nm), 1.5 parts of carbon black, 1.8 parts of styrene-butadiene rubber and 1.2 parts of sodium carboxymethyl cellulose.

[0061] The method for preparing the negative electrode sheet includes the following steps:

[0062] Silver nitrate and sodium citrate were dissolved in deionized water, and ascorbic acid solution was slowly added dropwise. The reaction was carried out at 70°C for 2 hours. After centrifugation and washing, the metal catalyst was obtained. The mass ratio of silver nitrate, sodium citrate and ascorbic acid was 1:1:1.2.

[0063] According to the formula, the first active material, carbon nanotubes, styrene-butadiene rubber, sodium carboxymethyl cellulose, metal catalyst and deionized water are mixed to obtain the first slurry;

[0064] According to the formula, the second active material, lithium titanium aluminum phosphate, carbon black, styrene-butadiene rubber, sodium carboxymethyl cellulose and deionized water are mixed to obtain the second slurry;

[0065] A double-layer coating machine is used to coat the first slurry and the second slurry onto the copper foil in sequence. After drying and rolling, the negative electrode sheet is obtained.

[0066] Example 2

[0067] This embodiment provides a negative electrode sheet, which includes a current collector (specifically an 8μm thick copper foil) and a first active layer with a thickness of 65μm and a second active layer with a thickness of 35μm, which are sequentially stacked on one side surface of the current collector.

[0068] In the first active layer, based on a mass fraction of 100 parts of the first active material, the first active layer comprises 100 parts of the first active material (D50 is 12 μm, compaction density is 1.65 g / cm³). 3 Its specific surface area is 1.5m². 2 / g of capacity-type artificial graphite material with a graphitization degree of 93%, 3 parts of carbon nanotubes, 1.5 parts of styrene-butadiene rubber, 1.5 parts of sodium carboxymethyl cellulose and 0.05 parts of metal catalyst; the metal catalyst is silver nanoparticles with a particle size D50 of 30nm and a main crystal plane of (111), wherein the X-ray diffraction peak intensity of the (111) crystal plane accounts for 85% of the total intensity of the X-ray diffraction peaks of all crystal planes;

[0069] In the second active layer, based on a mass fraction of 100 parts of the second active material, the second active layer comprises 100 parts of the second active material (particle size D50 of 5 μm and compaction density of 1.55 g / cm³). 3 Its specific surface area is 2.5 m². 2 / g of fast-charging artificial graphite material with a graphitization degree of 90%, 5 parts of lithium titanium aluminum phosphate (particle size D50 of 50nm), 1 part of carbon black, 1 part of styrene-butadiene rubber and 1 part of sodium carboxymethyl cellulose.

[0070] The method for preparing the negative electrode sheet includes the following steps:

[0071] Silver nitrate and sodium citrate were dissolved in deionized water, and ascorbic acid solution was slowly added dropwise. The reaction was carried out at 60°C for 3 hours. After centrifugation and washing, the metal catalyst was obtained. The mass ratio of silver nitrate, sodium citrate and ascorbic acid was 1:2:1.5.

[0072] According to the formula, the first active material, carbon nanotubes, styrene-butadiene rubber, sodium carboxymethyl cellulose, metal catalyst and deionized water are mixed to obtain the first slurry;

[0073] According to the formula, the second active material, lithium titanium aluminum phosphate, carbon black, styrene-butadiene rubber, sodium carboxymethyl cellulose and deionized water are mixed to obtain the second slurry;

[0074] A double-layer coating machine is used to coat the first slurry and the second slurry onto the copper foil in sequence. After drying and rolling, the negative electrode sheet is obtained.

[0075] Example 3

[0076] This embodiment provides a negative electrode sheet, which includes a current collector (specifically an 8μm thick copper foil) and a first active layer with a thickness of 45μm and a second active layer with a thickness of 25μm, which are sequentially stacked on one side surface of the current collector.

[0077] In the first active layer, based on a mass fraction of 100 parts of the first active material, the first active layer comprises 100 parts of the first active material (D50 is 18 μm, compaction density is 1.8 g / cm³). 3 Its specific surface area is 1.2 m². 2 / g of capacity-type artificial graphite material with a graphitization degree of 95%, 1 part of carbon nanotubes, 1 part of styrene-butadiene rubber, 1 part of sodium carboxymethyl cellulose and 0.5 parts of metal catalyst; the metal catalyst is silver nanoparticles with a particle size D50 of 100nm and a main crystal plane of (111), wherein the X-ray diffraction peak intensity of the (111) crystal plane accounts for 80% of the total intensity of the X-ray diffraction peaks of all crystal planes;

[0078] In the second active layer, based on a mass fraction of 100 parts of the second active material, the second active layer comprises 100 parts of the second active material (particle size D50 of 12 μm and compaction density of 1.48 g / cm³). 3 Its specific surface area is 3.0 m². 2 / g of fast-charging artificial graphite material with a graphitization degree of 93%, 2 parts of lithium titanium aluminum phosphate (particle size D50 of 200nm), 2 parts of carbon black, 1 part of styrene-butadiene rubber and 1 part of sodium carboxymethyl cellulose.

[0079] The method for preparing the negative electrode sheet includes the following steps:

[0080] Silver nitrate and sodium citrate were dissolved in deionized water, and ascorbic acid solution was slowly added dropwise. The reaction was carried out at 90°C for 1.5 hours. After centrifugation and washing, the metal catalyst was obtained. The mass ratio of silver nitrate, sodium citrate and ascorbic acid was 1:0.5:0.8.

[0081] According to the formula, the first active material, carbon nanotubes, styrene-butadiene rubber, sodium carboxymethyl cellulose, metal catalyst and deionized water are mixed to obtain the first slurry;

[0082] According to the formula, the second active material, lithium titanium aluminum phosphate, carbon black, styrene-butadiene rubber, sodium carboxymethyl cellulose and deionized water are mixed to obtain the second slurry;

[0083] A double-layer coating machine is used to coat the first slurry and the second slurry onto the copper foil in sequence. After drying and rolling, the negative electrode sheet is obtained.

[0084] Example 4

[0085] This embodiment provides a negative electrode sheet, which is the same as that in Example 1 except that the amount of metal catalyst is 0.02 parts.

[0086] Example 5

[0087] This embodiment provides a negative electrode sheet, which is the same as in Example 1 except that the metal catalyst content is 0.8 parts.

[0088] Example 6

[0089] This embodiment provides a negative electrode sheet, which is the same as that in Embodiment 1 except that the proportion of lithium aluminum titanium phosphate is 1 part.

[0090] Example 7

[0091] This embodiment provides a negative electrode sheet, which is the same as that in Embodiment 1 except that the proportion of lithium titanium aluminum phosphate is 8 parts.

[0092] Example 8

[0093] This embodiment provides a negative electrode sheet, which is the same as in Example 1 except that the X-ray diffraction peak intensity of the (111) crystal plane in the silver nanoparticles accounts for 70% of the total intensity of the X-ray diffraction peaks of all crystal planes (achieved by adjusting the mass ratio of sodium citrate to silver nitrate to 0.2:1 and lowering the reaction temperature to 50°C when preparing the silver nanoparticles).

[0094] Comparative Example 1

[0095] This comparative example provides a negative electrode sheet, which is the same as that in Example 1 except that the first active layer does not contain a metal catalyst.

[0096] Comparative Example 2

[0097] This comparative example provides a negative electrode sheet, which is the same as in Example 1 except that the metal catalyst and other materials are replaced by commercially available Ag nanoparticles without specific crystal orientation (the intensity of the (111) crystal plane diffraction peak in the XRD pattern accounts for 55%).

[0098] Comparative Example 3

[0099] This comparative example provides a negative electrode sheet, which is the same as that in Example 1 except that the second active layer does not contain lithium aluminum titanium phosphate.

[0100] The negative electrode sheets obtained in the above embodiments and comparative examples were subjected to performance testing. The testing methods are as follows:

[0101] (1) Exchange current density (i)o Test: The negative electrode to be tested was assembled into a CR2032 coin cell (with a lithium counter electrode). Tafel analysis was performed on an electrochemical workstation at a scan rate of 1 mV / s and a scan range of ±150 mV relative to the open circuit potential. The exchange current density i of the lithium deposition / dissolution reaction was calculated using the Tafel extrapolation method. o .

[0102] (2) Observation of lithium plating: The button half-cells prepared above were charged with constant current at different rates (1C, 2C, 3C). After being charged to the cutoff voltage, they were immediately disassembled and the surface morphology of the negative electrode was observed with a scanning electron microscope to determine whether lithium dendrites were present.

[0103] (3) Cyclic performance: The negative electrode obtained in the above examples and comparative examples were assembled with the NCM811 positive electrode into a soft-pack full cell. The cells were charged and discharged under 1C / 1C conditions, and the capacity retention rate was recorded after 500 cycles.

[0104] The test results are shown in Table 1 below:

[0105] Table 1

[0106]

[0107] As can be seen from Table 1 above:

[0108] (1) The negative electrode sheet described in this invention can improve fast charging performance and suppress lithium plating: Under 3C high-rate charging, there is no lithium plating on the negative electrode surface. Compared with Comparative Example 1 without catalyst, the lithium plating initiation current density is increased by more than 100%, and the lithium deposition overpotential is also reduced: According to Tafel curve test, compared with Comparative Example 1 without catalyst, the exchange current density of lithium deposition-dissolution reaction is increased by 3-4 times, the overpotential is reduced by more than 50mV, the kinetic performance is significantly improved, and the cycle life can be extended: Under 1C / 1C cycling conditions, the capacity retention rate is greater than 85% after 500 cycles.

[0109] (2) As can be seen from Example 1 and Comparative Example 1, compared with Comparative Example 1 which did not add silver nanoparticles with a specific crystal face, the exchange current density of the present invention is greatly improved, which can significantly improve the lithium deposition phenomenon, and at the same time improve the rate performance and cycle performance; As can be seen from Example 1 and Comparative Example 2, the catalytic effect of Ag particles without a specific crystal face orientation is greatly weakened. The present invention utilizes the unique adsorption and reduction catalytic effect of silver nanoparticles with a (111) crystal face on lithium ions, which reduces the lithium deposition overpotential and can significantly improve the lithium deposition problem; As can be seen from Example 1 and Comparative Example 3, even if the first active layer of the present invention contains a metal catalyst, the second active layer does not contain a solid electrolyte material, which will also weaken the overall performance of the negative electrode due to the obstruction of ion transport; As can be seen from Example 1 and Examples 4-5, the amount of silver nanoparticles added in Example 4 is too small, resulting in insufficient catalytic sites and a decrease in battery performance. The amount of silver nanoparticles added in Example 5 is too large, which dilutes the capacity and causes localization. The current is concentrated, and although the absolute value of i0 is still relatively high, the cycling and lithium plating morphology deteriorate. Therefore, the present invention preferably adds a specific amount of metal catalyst to exert its optimal effect. As can be seen from Examples 1 and 6-7, the amount of solid electrolyte material added in Example 6 is too small, the ion conduction is poor, the i0 value decreases and a small amount of lithium plating exists. The amount of solid electrolyte material added in Example 7 is too large, which aggravates electronic insulation and increases polarization, resulting in a decrease in i0 value and a decrease in cycling performance. Therefore, the amount of solid electrolyte material added in the present invention is preferably within a suitable range. As can be seen from Examples 1 and 8, when the proportion of the (111) facet of silver nanoparticles drops below 80%, the catalytic activity is weakened and the performance decreases. Therefore, in the silver nanoparticles of the present invention, the X-ray diffraction peak intensity of the (111) crystal facet preferably accounts for more than 80% of the total intensity of the X-ray diffraction peaks of all crystal faces, which can further exert its adsorption and reduction catalysis effects, thereby further improving the performance of the negative electrode.

[0110] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A negative electrode sheet, characterized in that, The negative electrode sheet includes a current collector and a coating on at least one side surface of the current collector. The coating includes a first active layer and a second active layer stacked sequentially. The first active layer is disposed on the surface of the current collector, and the second active layer is disposed on the side surface of the first active layer away from the current collector. The first active layer includes a first active material, a first conductive agent, a first binder, and a metal catalyst, wherein the metal catalyst includes silver nanoparticles with a (111) facet as the main crystal plane; The second active layer includes a second active material, a solid electrolyte material, a second conductive agent, and a second binder.

2. The negative electrode sheet according to claim 1, characterized in that, In the silver nanoparticles with the (111) plane as the main crystal plane, the X-ray diffraction peak intensity of the (111) crystal plane accounts for more than 80% of the total intensity of the X-ray diffraction peaks of all crystal planes. And / or, the particle size D50 of the silver nanoparticles with the main crystal plane being (111) is 30nm-100nm.

3. The negative electrode sheet according to claim 1 or 2, characterized in that, In the first active layer, based on 100 parts by mass of the first active material, the metal catalyst comprises 0.05 to 0.5 parts. And / or, in the first active layer, based on 100 parts by mass of the first active material, the number of parts of the first conductive agent is 1 to 3. And / or, in the first active layer, the first adhesive comprises 1 to 3 parts, based on 100 parts by mass of the first active material.

4. The negative electrode sheet according to claim 1 or 2, characterized in that, The first active material includes a capacity-type negative electrode active material, which includes a capacity-type graphite material and / or a silicon-carbon composite material; And / or, the first conductive agent includes any one or a combination of at least two of carbon black, carbon nanotubes, or graphene; And / or, the first adhesive comprises any one or a combination of at least two of styrene-butadiene rubber, sodium carboxymethyl cellulose, or polyacrylic acid.

5. The negative electrode sheet according to claim 1 or 2, characterized in that, In the second active layer, based on 100 parts by mass of the second active material, the number of parts of the solid electrolyte material is 2 to 5. And / or, in the second active layer, the second conductive agent comprises 1 to 2 parts, based on 100 parts by mass of the second active material; And / or, in the second active layer, the second adhesive comprises 1 to 3 parts, based on 100 parts by mass of the second active material.

6. The negative electrode sheet according to claim 1 or 2, characterized in that, The solid electrolyte material includes any one or a combination of at least two of lithium titanium aluminum phosphate, lithium germanium aluminum phosphate, lithium lanthanum zirconium oxide, or lithium lanthanum titanium oxide. And / or, the particle size D50 of the solid electrolyte material is 50nm-200nm; And / or, the second active material includes a fast-charging negative electrode active material, wherein the fast-charging negative electrode active material includes a fast-charging artificial graphite material; And / or, the particle size D50 of the second active material is 5 μm-12 μm; And / or, the second conductive agent comprises carbon black and / or carbon nanotubes; And / or, the second adhesive comprises styrene-butadiene rubber and / or sodium carboxymethyl cellulose.

7. The negative electrode sheet according to claim 1 or 2, characterized in that, The ratio of the thickness of the first active layer to the thickness of the second active layer is (1.5-2.5):1; And / or, the thickness of the first active layer is 45μm-65μm; And / or, the thickness of the second active layer is 25μm-35μm.

8. The negative electrode sheet according to claim 1 or 2, characterized in that, The exchange current density of the lithium deposition-dissolution reaction of the negative electrode is i o i o ≥2.5mA / cm 2 .

9. A method for preparing a negative electrode sheet as described in any one of claims 1-8, characterized in that, The preparation method includes the following steps: The first active material, the first conductive agent, the first binder, the metal catalyst and the first solvent are mixed to obtain the first slurry; The second active material, the solid electrolyte material, the second conductive agent, the second binder, and the second solvent are mixed to obtain the second slurry; The first slurry and the second slurry are sequentially layered and coated on at least one side of the current collector, and the negative electrode sheet is obtained after drying and rolling.

10. A battery, characterized in that, The battery includes a negative electrode as described in any one of claims 1-8.

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