A dry method negative electrode sheet, a preparation method thereof and application thereof

Abstract

The application provides a dry-method negative electrode sheet and a preparation method and application thereof. The dry-method negative electrode sheet at least comprises a negative electrode current collector and a dry-method negative electrode active layer arranged on at least one side surface of the negative electrode current collector in a thickness direction of the negative electrode current collector. The dry-method negative electrode active layer comprises a negative electrode active material, a conductive agent and a binder. The uniformity of the binder in the dry-method negative electrode active layer is 85%-96%. The negative electrode active material comprises a silicon material, which includes but is not limited to silicon, silicon-carbon material and silicon-oxygen negative electrode material. The dry-method negative electrode sheet and the preparation method and application thereof can inhibit the expansion of the negative electrode active material and improve the safety performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power batteries, in particular to a dry-method negative electrode sheet and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries have many advantages such as high voltage, high capacity, long cycle life, low self-discharge efficiency, good safety performance, and are widely used in 3C / digital products, electric vehicles, energy storage and other fields. The negative electrode sheet is an important component of the lithium ion battery, and the composition and structure of the negative electrode sheet have a decisive influence on the electrochemical performance of the lithium ion battery.

[0003] Among many factors, the negative active material as an important component of the lithium ion battery has a particularly significant influence on the performance of the lithium ion battery. During the charge and discharge cycle of the battery, the negative active material will change in volume with the insertion and extraction of lithium ions, and in particular, silicon materials will often change in volume by 120% to 300% or even more than 300%, which will worsen the interface contact and thus lead to a decrease in battery performance. During the dry-method preparation of the negative electrode sheet, the volume expansion of the negative active material will cause the interface debonding of the negative active material and the conductive agent, the binder and other materials, thereby leading to the failure of the electrode structure during the charge and discharge process. By increasing the content of the binder between the negative active materials, the adverse effects caused by the expansion of the negative active material can be improved to some extent, but the charge and discharge performance, capacity decay and other properties of the battery will be affected. SUMMARY

[0004] The present application provides a dry-method negative electrode sheet and a preparation method and application thereof. By controlling the uniformity of the binder in the dry-method negative active layer, the expansion of the negative active material can be inhibited, the effective transmission of lithium ions and electrons can be promoted, the risk of dry-method negative active layer falling off and short circuit can be reduced, and the safety performance can be improved.

[0005] To solve the above technical problems, the present application provides a dry-method negative electrode sheet, which at least comprises:

[0006] a negative current collector;

[0007] a dry-method negative active layer, which is at least arranged on one side surface along the thickness direction of the negative current collector, the dry-method negative active layer comprising a negative active material, a conductive agent and a binder, the uniformity of the binder in the dry-method negative active layer being 85%-96%;

[0008] The negative active material comprises a silicon material, and the silicon material includes but is not limited to silicon, silicon-carbon material and silicon-oxygen negative electrode material.

[0009] In an embodiment of the present application, the binder in the dry negative active layer is in the form of nanofibers, the diameter d 50 of the nanofibers is 10 nm-50 nm, the diameter d 90 / d 10 ≤1.5, wherein d 50 is the diameter of the nanofibers when the cumulative amount of the nanofibers is 50% from small to large, d 10 is the diameter of the nanofibers when the cumulative amount of the nanofibers is 10% from small to large, and d 90 is the diameter of the nanofibers when the cumulative amount of the nanofibers is 90% from small to large.

[0010] In an embodiment of the present application, the silicon content of the negative active material is A wt%, the nanofibers of the binder cover the surface of the negative active material, the area coverage of the nanofibers on the negative active material is B%, and the dry negative active layer satisfies the following relationship: -55≤0.45A-B≤-45.

[0011] In an embodiment of the present application, the content of the binder in the dry negative active layer is 0.5 wt%-5 wt%.

[0012] In an embodiment of the present application, the negative active material further comprises a graphite-based material, and the graphite-based material comprises at least one of natural graphite or artificial graphite.

[0013] In an embodiment of the present application, the mass percentage of the silicon material in the negative active material is 0-100 wt%.

[0014] In an embodiment of the present application, the binder comprises one or more combinations of polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, ethylene-vinyl acetate copolymer, polypropylene, polyethylene, ethylene-octene copolymer, or polyimide.

[0015] And / or, the conductive agent is selected from at least one of graphite, graphene, carbon black, carbon fiber, and carbon nanotube.

[0016] The present application also provides a preparation method of a dry negative electrode sheet, comprising at least the following steps:

[0017] Screening binder particles of a preset median particle size;

[0018] Mixing the negative active material, the conductive agent, and the binder particles to obtain a mixture;

[0019] Performing fibrillation treatment on the mixture to obtain a fibrillated material;

[0020] Cooling the fibrillated material to a target temperature at a preset rate while applying shearing to obtain an intermediate product.

[0021] The intermediate product is subjected to a crushing granulation treatment to obtain a dry negative electrode material;

[0022] The dry negative electrode material is subjected to multi-roll continuous rolling film forming to obtain a dry negative electrode active layer;

[0023] The dry negative electrode active layer is compounded with a negative electrode current collector to obtain a dry negative electrode sheet.

[0024] In an embodiment of the present application, the preset median particle size of the binder particles is X1 μm, the diameter d of the nanofibers in the dry negative electrode active layer is X2 nm, and the following relationship is satisfied: -5≤0.2X1-X2≤5. 50 In an embodiment of the present application, the preset median particle size of the binder particles is X1 μm, the diameter d of the nanofibers in the dry negative electrode active layer is X2 nm, and the following relationship is satisfied: -5≤0.2X1-X2≤5.

[0025] The preset median particle size of the binder particles is 20-250 μm.

[0026] In an embodiment of the present application, the uniformity of the binder in the dry negative electrode active layer is X3%, and the following relationship is satisfied: 96≤0.054X1+X3≤100.

[0027] In an embodiment of the present application, when the negative electrode active material is pure silicon, the median particle size of the binder particles is 40 μm-60 μm, and the content of the binder in the dry negative electrode active layer is 2wt%-4wt%.

[0028] In an embodiment of the present application, the binder particles are sieved at a preset temperature, and the preset temperature is 5℃-20℃.

[0029] The fibrillation includes a first stage, a second stage and a third stage, in the first stage, the treatment temperature is 20℃-40℃, the linear speed of stirring is 20m / s-30m / s, and the stirring duration is 10min-30min; in the second stage, the treatment temperature is 60℃-80℃, the linear speed of stirring is 40m / s-60m / s, and the stirring duration is 10min-30min; in the third stage, the treatment temperature is 90℃-120℃, the linear speed of stirring is 60m / s-70m / s, and the stirring duration is 60min-120min.

[0030] The preset rate is 10℃ / min-15℃ / min, and the target temperature is 25℃-40℃.

[0031] Pulse shearing is applied in the cooling process, and one pulse shearing includes shearing at 8m / s-10m / s for 4s-6s and shearing at 3m / s-5m / s for 8s-12s.

[0032] The present application also provides a full solid-state lithium ion battery, which at least includes:

[0033] a positive electrode tab;

[0034] a negative electrode tab selected from the dry-method negative electrode tab described above, or obtained from the preparation method described above;

[0035] a solid-state electrolyte layer disposed between the positive electrode tab and the negative electrode tab.

[0036] In an embodiment of the present application, the negative electrode tab further comprises a solid-state electrolyte selected from at least one of an oxide solid-state electrolyte, a sulfide solid-state electrolyte, or a halide solid-state electrolyte.

[0037] The present application also provides an electronic device comprising the all-solid-state lithium ion battery described above.

[0038] In summary, the present application proposes a dry-method negative electrode tab, a preparation method and application thereof. By improving the uniformity of the binder in the dry-method negative active layer, the expansion of the negative active material can be inhibited. On the premise of ensuring the mechanical stability of the negative electrode tab, the effective transmission of lithium ions and electrons can be promoted, the performance of the negative electrode tab can be improved, the risk of dry-method negative active layer falling off and short circuit can be reduced, and the safety performance can be improved. DETAILED DESCRIPTION

[0039] The present application will be described in more detail by the following specific examples. Other advantages and effects of the present application, which could be easily understood by those skilled in the art, can be easily understood from the contents disclosed in this specification. The present application can also be implemented or applied by different specific embodiments, and the details in the specification can be modified or changed based on different views and applications without departing from the spirit of the present application.

[0040] It should be understood that the present application can be implemented in different forms, and should not be interpreted as being limited to the embodiments presented herein. On the contrary, these embodiments are provided to make the disclosure complete and complete, and to fully convey the scope of the present application to those skilled in the art.

[0041] The technical solutions of the present application will be further described in detail below in combination with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0042] The present application provides a dry negative electrode sheet, which comprises at least a negative current collector and a dry negative active layer, the dry negative active layer is arranged on at least one side surface of the negative current collector along the thickness direction of the negative current collector, and the dry negative active layer comprises a negative active material, a conductive agent, a binder and the like. The uniformity of the binder in the dry negative active layer is, for example, 85%-96%. The negative active material comprises a silicon material, which includes but is not limited to silicon, silicon-carbon material and silicon-oxygen negative electrode material (SiO x , 0 The binder is used to connect the negative active material and the conductive agent and the like to each other, but the binder is an insulating substance. If the distribution of the binder is uneven, the powdering or the increase of the insulating area will lead to the decrease of the ion passage. The uniformity is defined as the dispersion degree of the distribution of the binder in a plurality of detection areas of the negative electrode sheet, and the dispersion degree and the uniformity are negatively correlated. In the dry negative electrode sheet provided by the present application, by improving the uniformity of the binder in the dry negative active layer, the expansion of the negative active material can be inhibited, the effective transmission of lithium ions and electrons can be promoted under the premise of ensuring the mechanical stability of the negative electrode sheet, the performance of the negative electrode sheet can be improved, the risk of the dry negative active layer falling off and short circuit can be reduced, and the safety performance can be improved.

[0043] In an embodiment of the present application, the existing form of the binder in the dry negative active layer is nanofiber, which forms a three-dimensional nanometer network structure. The diameter d 50 of the nanofiber is 10nm-50nm, the d 90 / d 10 is ≤1.5, wherein d 50 is the diameter when the cumulative amount of the nanofiber diameter from small to large is 50%, d 10 is the diameter when the cumulative amount of the nanofiber diameter from small to large is 10%, and d 90 is the diameter when the cumulative amount of the nanofiber diameter from small to large is 90%. If the diameter of the nanofiber is too small, the cohesion will be too low, which cannot inhibit the expansion of the negative active material, resulting in problems such as particle pulverization, collapse of the conductive network, electrode falling off or interface contact failure. On the contrary, if the diameter of the nanofiber is too large, although the strength of the nanofiber is increased, the insulating area between the negative active materials will be increased, and the ion passage will be reduced. Therefore, the appropriate nanodiameter of the binder needs to be selected, which can not only ensure the strength of the three-dimensional nanometer network structure and the sufficient cohesion to inhibit the expansion of the negative active material and avoid the dry negative electrode sheet being too fragile, but also make the passage more and smoother and improve the ion transmission capacity. Meanwhile, d 90 / d 10≤1.5, that is, the uniformity of the thickness of the nanofiber diameter is high, the distribution is uniform, which is conducive to improving the uniformity of the binder in the dry method negative active layer, and can avoid the ion transmission being blocked due to the local fiber being too thick, and can also avoid the local mechanical strength being insufficient due to the local fiber being too thin, thereby improving the performance of the dry method negative electrode sheet.

[0044] In an embodiment of the present application, the binder includes one or more combinations of Polytetrafluoroethylene (PTFE), Ethylene-tetra-fluoro-ethylene (ETFE), Ethylene-Vinyl Acetate Copolymer (EVA), Polypropylene (PP), Polyethylene (PE), Ethylene-octene copolymer, or Polyimide (PI), etc., and the molecular weight of the binder is, for example, 6000 kg / mol-8000 kg / mol, so as to improve the bonding performance of the binder and the strength of the formed nanofiber, and the content of the binder in the dry method negative active layer is, for example, 0.5wt%-5wt%. When the content of the binder is small, the cohesion of the dry method negative electrode sheet is small; when the content of the binder is large, the content of the binder inside the dry method negative active layer is too high, which leads to an increase in the diameter of the nanofiber and a decrease in the uniformity of the distribution, thereby reducing the number of ion channels. Therefore, by controlling the content of the binder, the strength and the conductive performance of the negative electrode sheet can be improved.

[0045] In an embodiment of the present application, the negative active material further includes a graphite-based material, which includes, for example, at least one of natural graphite or artificial graphite, the natural graphite includes, for example, at least one of block graphite, flaky graphite, or earthy graphite, and the artificial graphite includes, for example, at least one of single crystal graphite, polycrystalline graphite, pyrolytic graphite, or graphite fiber. The mass percentage of the silicon material in the negative active material is, for example, 0-100wt%, for example, 0, 10wt%, 13wt%, 26wt%, 50wt%, or 100wt%, etc.

[0046] In an embodiment of the present application, the content of silicon in the negative active material is A wt%, the nanofiber of the binder is wound on the surface of the negative active material, the area coverage of the nanofiber on the negative active material is B %, and the dry method negative active layer satisfies the following relationship: -55≤0.45A-B≤-45. When the content of silicon increases, the expansion of the negative active material intensifies, and by increasing the area coverage of the nanofiber on the negative active material, the inhibition effect of the expansion increases, therefore, by controlling the relationship between the content of silicon in the negative active material and the area coverage of the nanofiber on the negative active material, the strength of the electrode sheet can be improved while inhibiting the expansion.

[0047] In an embodiment of the present application, the conductive agent is selected from at least one of graphite, graphene, carbon black, carbon fiber, or carbon nanotube, and the content of the conductive agent in the dry negative active layer is, for example, 1wt%-5wt%. The carbon black is, for example, conductive carbon black (Super p), and the carbon fiber includes, for example, at least one of carbon nanofiber (CNF), vapor grown carbon fiber (VGCF), or vapor grown carbon nanofiber (VGCNF). In an embodiment of the present application, the conductive agent includes, for example, carbon black and carbon fiber, and the mass ratio of the carbon black to the carbon fiber is, for example, 1:(0.2-1.5), and for example, 1:1.

[0048] In an embodiment of the present application, the dry negative active layer further includes a solid-state electrolyte, and the solid-state electrolyte is selected from at least one of oxide solid-state electrolyte, sulfide solid-state electrolyte, and halide solid-state electrolyte, and for example, Li7La3Zr2O12, Li10SnP2S12, Li6PS5Cl, Li3InCl6, or Li3YCl6. When the dry negative active layer includes the solid-state electrolyte, the mass ratio of the negative active material, the solid-state electrolyte, the conductive agent, and the binder is, for example, (60-93):(5.5-30):(1-5):(0.5-5). 12 13 17 10 12 2 2 2

[0049] ​​​​​​​​In an embodiment of the present application, the negative current collector is for example a carbon-coated copper foil, and the carbon coating layer mainly comprises a conductive carbon material and a binder. The conductive carbon material comprises one or more of conductive carbon black, acetylene black or carbon nanotubes, and the binder comprises one or more of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA) or ethylene-vinyl acetate copolymer. The mass ratio of the conductive carbon material to the binder is for example 60-95:5-40, and the thickness of the carbon coating layer is for example 1-3 μm, so as to improve the conductivity between the dry-method negative active layer and the negative current collector. In other embodiments, the current collector can also use other negative current collectors commonly used in the art.

[0050] Based on the above dry-method negative electrode sheet, the present application further provides a preparation method of a dry-method negative electrode sheet, at least comprising: screening binder particles with a preset median particle size; mixing a negative active material, a conductive agent and the binder particles to obtain a mixture; performing fibrillation treatment on the mixture to obtain a fibrillated material; cooling the fibrillated material to a target temperature at a preset rate while applying shearing to obtain an intermediate product; performing crushing and granulation treatment on the intermediate product to obtain a dry-method negative electrode material; forming a film of the dry-method negative electrode material through multi-roll continuous rolling to obtain a dry-method negative active layer; and compounding the dry-method negative active layer with a negative current collector to obtain the dry-method negative electrode sheet.

[0051] In an embodiment of the present application, the binder is cooled to a brittle point of -40℃, and a closed-loop heat preservation crushing device is used for grinding to obtain a ground binder. The ground binder is screened through a screen with different pore sizes to obtain PTFE particles with a preset median particle size. The median particle size D50 refers to the particle size value corresponding to the cumulative volume distribution percentage of 50% in the volume distribution curve. In this embodiment, the pore size of the screen is for example 20-270 μm, and the preset temperature is for example 5-20℃. Screening at the preset temperature can prevent the binder from agglomerating due to excessively high temperature, so as to obtain solid binder particles, and the preset median particle size of the obtained binder particles is for example 20-250 μm.

[0052] In an embodiment of the present application, the negative active material and the conductive agent are mixed to obtain a premix. Optionally, the premix further comprises the solid-state electrolyte, in which case the negative active material, the solid-state electrolyte and the conductive agent are mixed to obtain the premix, and the premix and the binder particles are mixed to obtain the mixture. In the process of obtaining the premix, the components of the premix are mixed more uniformly by stirring, for example, the linear speed of stirring is controlled to be 20-40 m / s, the stirring time is controlled to be 20-60 min, and the processing temperature is controlled to be 5-60℃. In the process of obtaining the mixture, the components of the mixture are mixed more uniformly by stirring, for example, the linear speed of stirring is controlled to be 5-20 m / s, the stirring time is controlled to be 20-60 min, and the processing temperature is controlled to be 5-20℃. In the process of obtaining the premix, the linear speed is increased to improve the uniformity of the mixing of the components other than the binder. In the process of obtaining the mixture, the processing temperature (for example, the temperature during stirring of the mixture is lower than the temperature during stirring of the premix) and the linear speed are controlled to avoid problems such as agglomeration or local overheating of the binder particles caused by excessively high temperature, thereby avoiding uneven dispersion of the binder particles in the mixture.

[0053] In an embodiment of the present application, the mixture is subjected to fibrillation treatment to obtain a fibrillated material. In this embodiment, the fibrillation includes a first stage, a second stage and a third stage. In the first stage, the processing temperature is for example 20-40℃, the linear speed of stirring is for example 20-30 m / s, and the stirring time is for example 10-30 min. In the second stage, the processing temperature is for example 60-80℃, the linear speed of stirring is for example 40-60 m / s, and the stirring time is for example 10-30 min. In the third stage, the processing temperature is for example 90-120℃, the linear speed of stirring is for example 60-70 m / s, and the stirring time is for example 60-120 min. Through three-stage fibrillation treatment, the stepwise temperature increase and the segmented speed-up shear are cooperated to avoid excessive breakage or agglomeration of the binder, and through the high linear speed and time in the third stage, the maximum uniformity that the binder can achieve is maximized, thereby converting the binder particles into nanofibers, and the nanofibers form a uniform and dense three-dimensional network structure, thereby improving the strength of the subsequent obtained negative electrode sheet. In this embodiment, due to the limitations of the manufacturing process, the obtained nanofibers have a d 90 / d 10 ≥1.2.

[0054] In an embodiment of the present application, after the fibrillation treatment step, the fibrillated material is cooled to a target temperature at a preset rate, for example, 10℃ / min-15℃ / min, and the target temperature is, for example, 25℃-40℃. During the cooling process, shear is applied simultaneously to obtain an intermediate product. In this embodiment, the shear is, for example, pulse shear, and one pulse shear includes shearing at 8m / s-10m / s for 4s-6s and shearing at 3m / s-5m / s for 8s-12s. By rapid cooling and pulse shear, the fiber structure can be locked, and fiber shrinkage caused by natural cooling can be avoided, so that the size and distribution state of the nanofiber can be stabilized, and a high uniformity of the binder distribution can be obtained. At the same time, by means of stepwise temperature rise, segmented speed-up shear, rapid cooling and pulse shear, the d 90 / d 10 of the nanofiber formed by the binder can be reduced, and the uniformity of the nanofiber diameter can be improved.

[0055] In an embodiment of the present application, the intermediate product is subjected to a crushing and granulation treatment to obtain a dry method negative electrode material, the dry method negative electrode material is formed into a film by multi-roll continuous rolling, and is thinned to a set surface capacity, for example, 1mAh / cm 2 -10mAh / cm 2 to obtain a dry method negative electrode active layer. The dry method negative electrode active layer is combined with a negative electrode current collector to obtain a dry method negative electrode sheet, for example, the dry method negative electrode active layer is combined with a carbon-coated layer of the negative electrode current collector, and the dry method negative electrode active layer is combined with the negative electrode current collector under the action of a pressure, for example, 0.8ton-1.2ton (ton), at a temperature, for example, 20℃-100℃. By adjusting the parameters in the preparation of the dry method negative electrode sheet, the distribution of each component in the dry method negative electrode active layer is more uniform, and the fibrillation effect of the binder is better, so that a dry method negative electrode sheet with better performance is prepared, and the capacity of the battery is improved.

[0056] In an embodiment of the present application, the median particle size of the binder particles is X1μm, and the diameter d 50X2nm, satisfying the relationship: -5≤0.2X1-X2≤5. That is, the smaller the median particle size of the binder particles, the finer the diameter of the binder nanofiber obtained in the dry method negative electrode active layer, the nanofiber is fragile, resulting in a decrease in cohesion, and the expansion of silicon cannot be inhibited. When the median particle size of the binder particles is large, the diameter of the binder nanofiber obtained is large, the ion path is reduced, which is not conducive to ion transmission, and the fiber network formed by the large particle binder during the fiberization process is coarse, and the physical entanglement between the fibers is less, which can result in weak cohesion, that is, the cohesion increases first and then decreases with the increase of the fiber diameter, and at a certain particle size value of the binder particles less than 50 μm, the cohesion of the dry method negative electrode sheet changes, which is an inflection point. At the same time, the large particle binder has poor dispersibility, which can easily lead to uneven distribution of the binder. Therefore, by controlling the particle size of the binder particles, the diameter of the binder nanofiber distributed between the negative electrode active materials is within a certain range, which can provide appropriate cohesion to inhibit the expansion of the negative electrode active material, and the appropriate nanofiber diameter can provide more ion paths, which can improve the performance of the dry method negative electrode sheet. At the same time, by controlling the particle size and content of the binder to meet a certain range, a dry method negative electrode sheet with excellent performance can be prepared, which can inhibit the expansion of the negative electrode active material, reduce the problems of sheet powdering, cracking, electrode peeling, etc., and thus improve the capacity and cycle performance of the full solid-state battery.

[0057] In an embodiment of the present application, the area coverage of the nanofiber on the negative electrode active material and the diameter d 50 of the nanofiber in the dry method negative electrode active layer are negatively correlated, that is, the area coverage of the nanofiber on the negative electrode active material increases with the decrease of the diameter d 50 of the nanofiber, and the area coverage of the nanofiber on the negative electrode active material and the content of the binder in the dry method negative electrode active layer are positively correlated, that is, when the preparation method and other conditions are the same, the area coverage of the nanofiber on the negative electrode active material increases with the increase of the content of the binder. When the median particle size D50 of the binder particles is ≥50 μm, the better the expansion rate is inhibited with the increase of the area coverage of the nanofiber on the negative electrode active material, but when the median particle size D50 of the binder particles is <50 μm, the strength and cohesion of the nanofiber need to be considered, and the area coverage of the nanofiber on the negative electrode active material increases with the decrease of the nanofiber, but the nanofiber is too small in strength, which can also not be able to inhibit the expansion. Therefore, multiple factors such as uniformity, d 50 of the nanofiber, and area coverage need to be combined to ensure the effect of inhibiting expansion.

[0058] In an embodiment of the present application, when the uniformity of the binder in the dry-method negative active layer is, for example, X3%, the following relationship is satisfied: 96≤0.054X1+X3≤100, that is, the smaller the particle size of the binder particles, the finer the diameter of the nanofiber of the binder obtained, the higher the uniformity of the binder in the dry-method negative active layer, and the ion conductivity can be improved. When the nanofiber of the binder is finer, the specific surface area of the ultra-fine nanofiber network is greatly improved, the surface area of the negative active material covered by the unit mass of the binder is increased by several times, the area coverage rate of the surface of the negative active material can be improved, but the strength of the single nanofiber is weakened and is easy to break under the expansion of the negative active material. Therefore, by comprehensively considering the requirements of the content of silicon in the negative electrode, the particle size of the binder particles, the diameter of the nanofiber, and the uniformity, the diameter and the distribution uniformity of the nanofiber of the binder are accurately controlled according to the negative active material with different silicon contents, the expansion of the negative active material is inhibited, and the strength and performance of the negative electrode sheet are balanced.

[0059] In an embodiment of the present application, when the negative active material is pure silicon, the median particle size of the binder particles is, for example, 40-60 μm, and the content of the binder in the dry-method negative active layer is, for example, 2-4 wt%. When the negative active material is pure silicon, the binder particles with a median particle size of 40-60 μm are selected, the diameter of the nanofiber formed can be controlled, the cohesion is improved, the uniformity of the binder is improved, and the corresponding area coverage rate on the surface of the negative active material can be obtained by the content of the binder, the strength of the nanofiber can be improved, the cohesion of the dry-method negative electrode sheet is improved, the expansion of the silicon material is inhibited, and the performance of the negative electrode sheet is improved.

[0060] The present application also provides a full-solid-state lithium ion battery, which comprises a positive electrode sheet, a negative electrode sheet, and a solid-state electrolyte layer, the solid-state electrolyte layer is arranged between the positive electrode sheet and the negative electrode sheet, and the negative electrode sheet is selected from the dry-method negative electrode sheet described above. In the present application, the full-solid-state battery is, for example, a primary battery or a secondary battery, and the secondary battery is, for example, a soft-packaged battery, a square can battery, or a cylindrical battery, and the present application does not specifically limit the type and category of the full-solid-state battery.

[0061] In an embodiment of the present application, the positive electrode sheet comprises a positive electrode current collector and a positive active layer coated on at least one side surface of the positive electrode current collector. The positive electrode current collector is, for example, a foil formed after surface treatment of nickel, titanium, aluminum, silver, stainless steel, or carbon, and the positive electrode current collector can also adopt any one or a combination of multiple forms such as a film, a net, a porous shape, a foam, or a non-woven fabric, etc.

[0062] In an embodiment of the present application, the positive electrode active layer comprises a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder, etc. The ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder can be selected according to actual needs. In this embodiment, the positive electrode active material, for example, comprises at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, or lithium-rich manganese-based oxide, etc. The positive electrode conductive agent, for example, is selected from at least one of conductive carbon black, acetylene black, carbon nanotubes, or graphene, etc., and the positive electrode binder, for example, is selected from at least one of polyvinylidene fluoride, poly(ethylene oxide) (PEO), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), or polyhexafluoropropylene, etc.

[0063] In an embodiment of the present application, the positive electrode active layer further comprises a solid-state electrolyte, which is selected from at least one of oxide solid-state electrolytes, sulfide solid-state electrolytes, and halide solid-state electrolytes, etc., and is further selected from at least one of Li7La3Zr2O 12 13 Al3Ti 17 (PO4)3, Li 10 GeP2S 12 , Li6PS5Cl, Li3InCl6, or Li3YCl6, etc. The mass ratio of the positive electrode active material, the solid-state electrolyte, the positive electrode conductive agent, and the positive electrode binder is, for example, (64-93.9):(5-30):(1-5):(0.1-1). The positive electrode active layer can be prepared by a dry method or a wet method, which is not specifically limited in the present application.

[0064] In an embodiment of the present application, the solid-state electrolyte layer comprises a solid-state electrolyte, which is selected from at least one of oxide solid-state electrolytes, sulfide solid-state electrolytes, and halide solid-state electrolytes, etc., and is further selected from at least one of Li7La3Zr2O 12 13 Al3Ti 17 (PO4)3, Li 10 GeP2S 12 ​​Li6PS5Cl, Li3InCl6, or Li3YCl6, or the like. The solid-state electrolyte is pressed, for example, at 90 MPa-150 MPa, to obtain a solid-state electrolyte layer. The dry cathode electrode sheet, the solid-state electrolyte layer, and the anode electrode sheet are sequentially placed in a mold for assembly, and after assembly, the pressure is increased to 100 MPa and the nut at the top of the post is tightened to a constant pressure, thereby obtaining a full solid-state lithium ion battery. The assembly process is completed in an argon atmosphere or under vacuum. In this embodiment, when the full solid-state lithium ion battery is assembled, the performance of the cathode electrode sheet is tested, for example, using an alloy including indium, lithium, aluminum, or at least two of the above metals as the counter electrode.

[0065] The present application will be explained more specifically below by referring to examples, which should not be construed as limiting. Appropriate modifications can be made within the scope consistent with the gist of the present application, which all fall within the technical scope of the present application.

[0066] Example 1

[0067] Screening of binder particles: PTFE is cooled to a brittle point of -40°C, ground using a closed-loop heat-preservation grinding device, and controlled to have a D50 of ≤ 250 μm after grinding to obtain ground PTFE. The PTFE is sieved through a screen having a pore size of 60 μm, and the PTFE particles that can pass through the screen are collected. The PTFE particles that pass through the screen are then sieved through a screen having a pore size of 40 μm, and the PTFE particles that cannot pass through the screen are collected. The PTFE has a median particle size of 50 μm, and the sieving is performed at a processing temperature of 10°C. The PTFE is obtained from Daikin Fluorochemicals (China) Co., Ltd., and has a molecular weight of 6000 kg / mol.

[0068] Preparation of dry cathode electrode sheet: pure silicon, Li6PS5Cl, Super p, and VGCF are mixed to obtain a premix, the stirring linear velocity is 30 m / s, the stirring duration is 30 min, and the processing temperature is 25°C, thereby obtaining the premix. The premix and the binder particles are mixed to obtain a mixture, the stirring linear velocity is 15 m / s, the stirring duration is 30 min, and the processing temperature is 10°C, thereby obtaining the mixture. The mixture is subjected to fibrillation treatment to obtain a fibrillated material, the first stage processing temperature is 25°C, the stirring linear velocity is 20 m / s, and the stirring duration is 10 min; the second stage processing temperature is 80°C, the stirring linear velocity is 50 m / s, and the stirring duration is 10 min; the third stage processing temperature is 120°C, the stirring linear velocity is 70 m / s, and the stirring duration is 90 min. After the fibrillation is completed, the fibrillated material is rapidly cooled to 25°C at a rate of 15°C / min, while pulse shear is applied, one pulse cycle is 10 m / s for 5 s and 5 m / s for 10 s. The fibrillated material is subjected to crushing and granulation treatment to obtain a dry cathode material. The dry cathode material is subjected to multi-roll continuous rolling to form a film and thinned to 4 mAh / cm2 The surface capacity of the dry method negative electrode active layer is obtained, the dry method negative electrode active layer is compounded with the carbon-coated aluminum foil to obtain the high-performance dry method negative electrode sheet, and the uniformity of the binder in the dry method negative electrode active layer is 94%.

[0069] The pure silicon is from Guangzhou Hongwu Material Technology Co., Ltd., and the model is A212. The solid-state electrolyte is Li6PS5Cl, which is from Shandong Xingjie New Energy Lithium Co., Ltd., and the model is LPSCl. The conductive agent is Super p and VGCF with a mass ratio of 1:1, Super p is from Tianjin Youmeng Chemical Co., Ltd., and VGCF is from Showa Denko K.K., and the model is VGCF-H. The carbon-coated layer of the carbon-coated copper foil is conductive carbon black and polyacrylic acid with a mass ratio of 8:2, and the thickness of the carbon-coated layer is 1 μm. The mass ratio of the negative electrode active material, Li6PS5Cl, Super p, VGCF and PTFE is 70:24:1.5:1.5:3.

[0070] The counter electrode: a lithium-indium alloy sheet is selected as the counter electrode.

[0071] Preparation of the solid-state electrolyte layer: 1000 mg of Li6PS5Cl powder is placed in a mold with a diameter of 10 mm, and is pressed to 100 MPa to obtain the solid-state electrolyte layer.

[0072] Preparation of the battery: the dry method negative electrode sheet, the solid-state electrolyte layer and the counter electrode are sequentially placed in a mold for assembly, and after assembly, the pressure is increased to 100 MPa and the nut at the top of the stand is tightened to constant pressure, thereby obtaining the all-solid-state lithium ion battery. The assembly process is completed in an argon atmosphere glove box, and the diameter of the dry method negative electrode sheet and the counter electrode is 10 mm.

[0073] Example 2

[0074] The screening process of the binder is adjusted, the obtained PTFE median particle size is 75 μm, and the negative electrode active material is a silicon-carbon material with a silicon content of 50%, which is from Changzhou Silicon Source New Energy Material Co., Ltd., and the model is NSC9100. The preparation steps of other batteries (including the preparation process of the solid-state electrolyte layer and the counter electrode, etc.) are the same as those of Example 1.

[0075] Example 3

[0076] The screening process of the binder is adjusted, the obtained PTFE median particle size is 100 μm, and the negative electrode active material is a silicon-carbon material with a silicon content of 26%, which is from Guangdong Chuguan New Energy Technology Co., Ltd., and the model is silicon-carbon material 1200. The preparation steps of other batteries are the same as those of Example 1.

[0077] Example 4

[0078] The screening process of the binder is adjusted, the PTFE median particle size is 155 μm, the negative active material is silicon-carbon material, and the silicon content is 13%, which is from Guangdong Candlelight New Energy Technology Co., Ltd., and the model is silicon-carbon material 650. The preparation steps of other batteries are the same as those of example 1.

[0079] Example 5

[0080] The screening process of the binder is adjusted, the PTFE median particle size is 250 μm, and the negative active material is graphite, which is from Betr New Material Group Co., Ltd., and the model is AGP-9. The preparation steps of other batteries are the same as those of example 1.

[0081] Example 6

[0082] The negative active material is silicon-carbon material, and the silicon content is 50%, which is from Changzhou Silicon Source New Energy Material Co., Ltd., and the model is NSC9100. The preparation steps of other batteries (including the solid electrolyte layer preparation process and the counter electrode) are the same as those of example 1.

[0083] Example 7

[0084] The content of the binder in the dry negative active layer is adjusted to 2 wt%, and the proportions of other components remain unchanged. The preparation steps of other batteries are the same as those of example 4.

[0085] Example 8

[0086] The content of the binder in the dry negative active layer is adjusted to 4 wt%, and the proportions of other components remain unchanged. The preparation steps of other batteries are the same as those of example 4.

[0087] Example 9

[0088] The screening process of the binder is adjusted, the PTFE median particle size is 75 μm, the content of the binder in the dry negative active layer is adjusted to 5 wt%, and the proportions of other components remain unchanged. The preparation steps of other batteries are the same as those of example 1.

[0089] Example 10

[0090] The screening process of the binder is adjusted, the PTFE median particle size is 100 μm, and the preparation steps of other batteries are the same as those of example 1.

[0091] Example 11

[0092] The molecular weight of the binder is 8000 kg / mol, which is from Daikin Fluorine Chemical Co., Ltd., and the model is F121. The preparation steps of other batteries are the same as those of example 4.

[0093] Example 12

[0094] The binder was replaced with ethylene-vinyl acetate copolymer, which was sourced from DuPont, USA, and the model was Elvax 40W. The other battery preparation steps were the same as those in Example 4.

[0095] Comparative Example 1

[0096] The screening process of the binder was adjusted to obtain a PTFE median particle size of 50 pm, and the negative active material was a silicon-carbon material with a silicon content of 13%, which was sourced from Guangdong Candlelight New Energy Technology Co., Ltd., and the model was silicon-carbon material 650. When obtaining the premix, the linear speed of stirring was 30 m / s, the stirring duration was 30 min, and the processing temperature was 25°C. When obtaining the mixture, the linear speed of stirring was 15 m / s, the stirring duration was 30 min, and the processing temperature was 10°C to obtain the mixture. The mixture was subjected to fibrillation treatment to obtain the fibrillated material, the linear speed of stirring was 50 m / s, the stirring duration was 20 min, and the third-stage processing temperature was 100°C. After the fibrillation was completed, natural cooling was performed to 25°C, and no pulse shear was applied during the cooling process. The other battery preparation steps were the same as those in Example 1.

[0097] Comparative Example 2

[0098] The screening process of the binder was adjusted to obtain a PTFE median particle size of 75 pm, and the other battery preparation steps were the same as those in Comparative Example 1.

[0099] Comparative Example 3

[0100] The screening process of the binder was adjusted to obtain a PTFE median particle size of 250 pm, and the other battery preparation steps were the same as those in Comparative Example 1.

[0101] Comparative Example 4

[0102] The binder was not subjected to the screening process, and the PTFE median particle size was 400 pm, and the other battery preparation steps were the same as those in Comparative Example 1.

[0103] Comparative Example 5

[0104] The binder was not subjected to the screening process, and the PTFE median particle size was 400 pm, and the negative active material was pure silicon, which was sourced from Guangzhou Hongwu Material Technology Co., Ltd., and the model was A212. The other battery preparation steps were the same as those in Comparative Example 1.

[0105] Comparative Example 6

[0106] The content of the binder in the dry negative active layer was adjusted to 10 wt%, and the proportions of the other components remained unchanged. The other battery preparation steps were the same as those in Comparative Example 5.

[0107] Comparative Example 7

[0108] The binder has a molecular weight of 2000 kg / mol, is from Daikin Fluorochemicals, and is model F104. The other battery preparation steps are the same as in Example 4.

[0109] In the present application, the reagents and raw materials used in Examples 1-12 and Comparative Examples 1-7 that are not otherwise labeled are commercially available. The dry-method negative electrode sheets and the all-solid-state lithium-ion batteries in Examples 1-12 and Comparative Examples 1-7 are subjected to performance testing, and the test results are recorded.

[0110] In an embodiment of the present application, to obtain the uniformity of the binder in the dry-method negative electrode active layer, the specific type of the binder in the electrode sheet can be confirmed by Fourier Transform infrared spectroscopy (FTIR) method, such as directly detecting the electrode sheet surface or scraping a powder sample, and determining the type of the binder by characteristic functional group peak position. After determining the type of the binder, the characteristic chemical bond of the binder is selected as the characterization object. The uniformity of the binder on the surface of the dry-method negative electrode sheet is observed by using Energy Dispersive Spectroscopy (EDS). Specifically, the uniformity of the binder distribution can be well observed by increasing the magnification to 5000 times. The specific process includes, first selecting the middle region of the electrode sheet as the observation object, optionally selecting 5 regions of 50 μm x 50 μm, and arranging the 5 regions along the same line with a center point spacing of 500 μm from each other, obtaining the proportion of different elements by EDS area scanning, and selecting the characteristic element of the binder as the result of the region, such as F element for PTFE. The ratio of the average and the mean difference of the F element content of the 5 regions is obtained, and 1 is subtracted from the ratio to obtain the result as the uniformity of the binder in the dry-method negative electrode sheet of a sample. Selecting 5 dry-method negative electrode sheets obtained in the same example or comparative example as parallel samples, obtaining the uniformity data of the binder of the 5 parallel samples, and taking the average value as the uniformity of the binder in the example or comparative example.

[0111] In an embodiment of the present application, the content of the binder is obtained by testing the characteristic element absorption peak of the binder by Fourier Transform infrared spectroscopy. For example, PTFE has a unique infrared absorption peak (such as C-F bond vibration peak at 1200 cm -1 -1300cm -1 , which can be quantitatively analyzed by FTIR. The operation steps are: grinding the dry-method negative electrode active layer sample into powder, mixing the powder with KBr and pressing a tablet, or directly using ATR (attenuated total reflection) mode testing, collecting the infrared spectrum of the sample, and quantitatively analyzing the content of PTFE in the dry-method negative electrode active layer by standard curve or peak area integration.

[0112] In an embodiment of the present application, the form of the binder in the dry-method negative electrode sheet is nanofiber, and the nanofiber diameter is tested by scanning electron microscopy (SEM) or transmission electron microscopy (TEM). The negative electrode sheet is placed in a testing device, and under a magnification of 50,000, fibers with a length greater than 5 μm are taken, and a point value width is taken every 200 nm along the fiber axis, the average value of the point value width is taken as the diameter of the fiber, 100 fibers are randomly taken, arranged from small to large in diameter, and the diameters at the 10th, 50th, and 90th positions are obtained, denoted as d 10 , d 50 , d 90 .

[0113] Five dry-method negative electrode sheets obtained in the same embodiment or comparative example are selected as parallel samples. The d 10 , d 50 , and d 90 of the nanofiber binder of each parallel sample are obtained as described above, and the d 50 , d 90 , and d 10 of the five parallel samples are obtained, and the d 50 , d 90 , and d 10 values of the embodiment or comparative example are obtained as the average values of the d

[0114] In an embodiment of the present application, after the binder is fiberized in the dry method, the area coverage of the nanofiber on the negative electrode active material is mainly tested by microscopic imaging combined with element analysis technology: five 50 μm×50 μm observation regions with a spacing of ≥100 μm are randomly selected in the central region of the negative electrode sheet, and SEM morphology imaging and EDS element surface scanning (for the F of the binder characteristic element such as PTFE) are simultaneously performed on each region; the total projection area of all active material particles in the region and the area covered by the characteristic element signal on the surface thereof are measured by image processing software, the coverage of a single region (binder coverage area / total active material area×100%) is calculated, and finally the arithmetic average of the coverage of the five regions is taken as the area coverage of the nanofiber on the negative electrode active material. The average value of the area coverage of the nanofiber on the negative electrode active material in the detection region of the five parallel samples is measured, which is the area coverage of the nanofiber on the negative electrode active material of the electrode sheet.

[0115] In an embodiment of the present application, in order to obtain the room temperature cycle performance, the full solid-state lithium ion batteries prepared in Examples 1-12 and Comparative Examples 1-7 were subjected to long cycle charging and discharging after being sized at 25°C, and the room temperature cycle number was measured. The test conditions were that the battery was sized and then subjected to long cycle charging and discharging test, and the first cycle sizing specific capacity was recorded during the process, and when the battery capacity reached 80% of the first cycle capacity (80% State of Health, 80% SOH), the test was ended, and the room temperature cycle number was obtained. The test voltage range was -0.615V-1.4V, the sizing current was 0.6mA, and the room temperature cycle test rate was 0.3C.

[0116] Table 1, part parameters of the dry cathode electrode sheet and battery performance in Examples 1-10 and Comparative Examples 1-6

[0117]

[0118] As shown in Table 1, it can be seen from Comparative Examples 1-5 that when the silicon content of the negative active material is different, under the same preparation conditions, the binder particles of different particle sizes are matched, and as the binder particle size increases, the d 50 of the binder nanofiber decreases, and the area coverage of the nanofiber to the negative active material decreases due to the increase of the nanofiber diameter. Among them, the smaller the nanofiber diameter, the lower the nanofiber strength, the higher the coverage, and the coverage and the ability to inhibit silicon expansion are positively correlated, so that when the silicon content changes, by controlling the D50 of the binder particles, the cohesion and coverage of the nanofiber diameter are considered, so that the expansion of the negative active material can be inhibited, and the cycle performance of the battery is ensured under the premise of improving the first cycle charging specific capacity.

[0119] As shown in Table 1, it can be seen from Comparative Examples 2 and 6 that when the silicon content is 50%, under the same preparation conditions, when the median particle size D50 of the binder particles is reduced to 50μm, the nanofiber diameter can be reduced, the uniformity and the area coverage of the nanofiber to the negative active material can be increased, and the cohesion of the nanofiber obtained at this time is sufficient, so that the cycle stability is improved, and the capacity is improved to a certain extent with high uniformity.

[0120] As shown in Table 1, it can be seen from Comparative Examples 4, 7-8 that when the silicon content in the negative active material is consistent, under the same preparation conditions, only the binder content is changed, and as the binder content increases, the d 50Increase, thereby the uniformity of binder fiber dispersion decreases, and the uniformity of the binder in the negative electrode sheet is reduced, but the area coverage of the nanofibers on the negative electrode active material increases, resulting in a decrease in the first-cycle charge capacity, but an increase in the cycle performance. Therefore, under the premise of the same silicon content, the binder content is controlled to achieve a balance between the first-cycle charge capacity and the cycle performance.

[0121] As shown in Table 1, a comparison of Examples 1, 9, and 10 shows that, under identical preparation conditions, while maintaining consistent silicon content in the negative electrode active material, varying both the median particle size (D50) and content of the binder particles simultaneously yielded similar binder uniformity. However, this resulted in an increase in the diameter of the binder nanofibers, a decrease in the nanofiber area coverage of the negative electrode active material, and failure to meet the requirement of -55 ≤ 0.45 AB ≤ -45. This weakened expansion suppression capability and, consequently, a rapid decline in cycling performance. Therefore, a balance of nanofiber diameter, uniformity, and coverage was crucial to improving battery cycling performance.

[0122] As shown in Table 1, by comparing Example 4 with Comparative Examples 1-4, it can be seen that when the silicon content and the binder content in the negative electrode active material are the same, and the preparation method does not adopt the preparation method provided by the present application, even if the median particle size D50 of the binder particles is reduced, the d 50 d 90 / d 10 The larger the value, the lower the uniformity of the binder is, and the smaller the value, the lower the area coverage of the negative electrode active material by the nanofibers is, and the smaller the value, the lower the area coverage of the negative electrode active material is, and the smaller the value, the lower the area coverage of the negative electrode active material is, and the smaller the value, the lower the area coverage of the negative electrode active material is, which deteriorates the performance of the battery. As the median particle size of the binder particles increases, the battery performance will further deteriorate.

[0123] As shown in Table 1, by comparing Example 1 with Comparative Examples 5-6, it can be seen that when the silicon content in the negative electrode active material is the same, the median particle size of the binder particles is a conventional particle size and the preparation method does not adopt the preparation method provided by this application, when the binder content is low, the area coverage of the nanofibers on the negative electrode active material is low and does not meet the requirement of -55≤0.45AB≤-45, and the battery cycle performance plummets. Increasing the binder content increases the d 50 The increase in the uniformity of the nanofibers resulted in a decrease in the first-cycle charge capacity. The area coverage of the nanofibers on the negative electrode active material increased compared to Comparative Example 5, resulting in a slight improvement in the cycling performance, but overall it was poor. Therefore, by controlling the median particle size of the binder particles and the preparation process, while ensuring the mechanical stability of the negative electrode sheet, the efficient transport of lithium ions and electrons was promoted, thereby improving the performance of the negative electrode sheet.

[0124] Table 2. Dry-process negative electrode plate parameters and battery performance in Examples 4, 11 and Comparative Example 7

[0125]

[0126] As shown in Table 2, it can be seen from Comparative Examples 4, 11 and Comparative Example 7 that, under the same preparation process, when the D50 and content of the binder particles are the same, only the molecular weight of the binder is changed, the obtained binder nanofiber d 50 , d 90 / d 10 and uniformity are the same, but as the molecular weight of the binder increases, the strength of the obtained nanofiber increases, thereby improving the performance of the negative electrode sheet, and thus the performance of the battery is improved.

[0127] Table 3, part of the parameters of the dry negative electrode sheet and the battery performance in Examples 4 and 12

[0128]

[0129] As shown in Table 3, it can be seen from Comparative Example 4 and Example 12 that, when different binders are selected, the particle size, content and preparation method of the binder are the same, the first circle discharge specific capacity and cycle performance of the battery are similar, and the d 50 , d 90 / d 10 and uniformity of the nanofiber are similar, which shows that when different binders are selected, by controlling the particle size and content of the binder, a negative electrode sheet with high uniformity can be obtained, thereby improving the performance of the battery.

[0130] The application further provides an electronic device comprising at least one all-solid-state lithium ion battery as described above, wherein the all-solid-state lithium ion battery is used to provide electric energy. The electronic device can be a vehicle, a mobile phone, a portable device, a notebook computer, a ship, a spacecraft, an electric toy, an electric tool, etc. In an embodiment of the application, the vehicle is a new energy vehicle, which can be a pure electric vehicle, a hybrid vehicle or a range extended vehicle, etc. The spacecraft includes an airplane, a rocket, a space shuttle and a spacecraft, etc. The electric toy includes a fixed or mobile electric toy, such as a game console, an electric vehicle toy, an electric ship toy and an electric airplane toy, etc. The electric tool includes a metal cutting electric tool, a grinding electric tool, an assembling electric tool and a railway electric tool, such as an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact drill, a concrete vibrator and an electric planer, etc. The electronic device comprises the all-solid-state lithium ion battery as described above, and thus has the advantages of the all-solid-state lithium ion battery as described above, which will not be described herein.

[0131] In summary, the present application proposes a dry method negative pole piece, its preparation method and application, by improving the uniformity of the binder in the dry method negative active layer, the expansion of the negative active material can be inhibited, the effective transmission of lithium ions and electrons can be promoted under the premise of ensuring the mechanical stability of the negative pole piece, the performance of the negative pole piece is improved, the risk of dry method negative active layer falling off and short circuit is reduced, and the safety performance is improved. The diameter of the binder nanofiber can be controlled, and the thickness distribution of the nanofiber diameter is uniform, so as to ensure the strength and sufficient cohesion of the three-dimensional nanometer network structure, inhibit the expansion problem of the negative active material, and improve the ion transmission capacity. By controlling the particle size and content of the binder to meet a certain range, the expansion problem of the negative active material can be inhibited, the problems of pole piece powder, cracking, electrode falling off and the like can be reduced, and the capacity and cycle performance of the full solid-state battery are improved. The requirements of negative electrode silicon content, binder particle size, nanofiber diameter and uniformity can be comprehensively met, the diameter and distribution uniformity of the binder nanofiber can be accurately controlled according to different silicon content of the negative active material, the expansion of the negative active material can be inhibited, and the strength and performance of the negative pole piece reach a balance.

[0132] The above description is only the preferred embodiment of the present application and the explanation of the applied technical principles, and those skilled in the art should understand that the scope of the application involved in the present application is not limited to the technical solutions formed by the specific combination of the above technical features, and should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept, for example, the technical solutions formed by replacing the above features with the technical features disclosed in the present application (but not limited to) having similar functions.

[0133] In addition to the technical features described in the specification, the remaining technical features are known to those skilled in the art, and in order to highlight the innovative features of the present application, the remaining technical features will not be described here.

Claims

1. A dry-process negative electrode sheet, characterized in that: At least: negative electrode current collector; A dry-process negative electrode active layer is provided on at least one surface along the thickness direction of the negative electrode current collector, wherein the dry-process negative electrode active layer comprises a negative electrode active material, a conductive agent, and a binder, wherein the uniformity of the binder in the dry-process negative electrode active layer is 85%-96%; The binder exists in the dry-process negative electrode active layer in the form of nanofibers, and the diameter of the nanofibers is d 50 10nm-50nm, d 90 / d 10 ≤1.5, where d 50 is the diameter of the nanofibers when the number of nanofibers increases from small to large to 50%, d 10 is the diameter of the nanofibers when the number of nanofibers from small to large accumulates to 10%, d 90 The diameter of the nanofibers when the cumulative number of nanofiber diameters from small to large reaches 90%; The negative electrode active material includes silicon materials, including but not limited to silicon, silicon-carbon materials and silicon-oxygen negative electrode materials; The uniformity is achieved by: The middle area of ​​the dry-process negative electrode sheet was selected as the observation object, and 5 50μm×50μm areas were randomly selected. The 5 areas were arranged along the same line with a center interval of 500μm. The proportions of different elements were obtained by surface scanning using energy dispersive X-ray spectroscopy. The characteristic elements of the binder were selected as the results of the area. The ratio of the mean difference and the average of the characteristic element contents of the 5 areas was obtained. The ratio was subtracted from 1 to obtain the uniformity of the binder in the dry-process negative electrode sheet.

2. The dry-process negative electrode sheet according to claim 1, characterized in that: The silicon content of the negative electrode active material is Awt%; the nanofibers of the binder cover the surface of the negative electrode active material, and the area coverage of the nanofibers on the negative electrode active material is B%. The dry-process negative electrode active layer satisfies the following relationship: -55≤0.45AB≤-45.

3. The dry-process negative electrode sheet according to claim 1, characterized in that: The content of the binder in the dry-process negative electrode active layer is 0.5 wt % to 5 wt %.

4. The dry-process negative electrode sheet according to claim 1, characterized in that: The negative electrode active material further includes a graphite material, and the graphite material includes at least one of natural graphite and artificial graphite.

5. The dry-process negative electrode sheet according to claim 4, characterized in that: The mass percentage of the silicon material to the negative electrode active material is 0-100 wt %.

6. The dry-process negative electrode sheet according to claim 1, characterized in that: The binder comprises one or more combinations of polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, ethylene-vinyl acetate copolymer, polypropylene, polyethylene, ethylene-octene copolymer or polyimide; And / or, the conductive agent is selected from at least one of graphite, graphene, carbon black, carbon fiber and carbon nanotubes.

7. A method for preparing a dry-process negative electrode sheet, for preparing the dry-process negative electrode sheet according to any one of claims 1 to 6, characterized in that: At least the following steps are included: Sieving binder particles with a preset median particle size; mixing the negative electrode active material, the conductive agent and the binder particles to obtain a mixed material; performing a fibrillation treatment on the mixed material to obtain a fibrillated material; Cooling the fibrillated material to a target temperature at a preset rate while applying shear to obtain an intermediate product; Crushing and granulating the intermediate product to obtain a dry-process negative electrode material; The dry-process negative electrode material is formed into a film by continuous rolling with multiple rollers to obtain a dry-process negative electrode active layer; The dry-process negative electrode active layer is compounded with the negative electrode current collector to obtain a dry-process negative electrode sheet.

8. The method for preparing a dry-process negative electrode sheet according to claim 7, characterized in that: The preset median particle size of the binder particles is X1 μm, and the diameter d of the nanofibers in the dry-process negative electrode active layer is 50 is X2 nm, satisfying the following relationship: -5≤0.2X1-X2≤5; The binder particles have a preset median particle size of 20 μm to 250 μm.

9. The method for preparing a dry-process negative electrode sheet according to claim 8, characterized in that: The uniformity of the binder in the dry-process negative electrode active layer is X3%, satisfying the following relationship: 96≤0.054X1+X3≤100.

10. The method for preparing a dry-process negative electrode sheet according to claim 7, characterized in that: When the negative electrode active material is pure silicon, the median particle size of the binder particles is 40 μm-60 μm, and the content of the binder in the dry-process negative electrode active layer is 2 wt %-4 wt %.

11. The method for preparing a dry-process negative electrode sheet according to claim 7, characterized in that: Sieving the binder particles at a preset temperature, wherein the preset temperature is 5° C.-20° C.; The fibrillation includes a first stage, a second stage and a third stage. In the first stage, the treatment temperature is 20°C-40°C, the stirring linear speed is 20m / s-30m / s, and the stirring time is 10min-30min; in the second stage, the treatment temperature is 60°C-80°C, the stirring linear speed is 40m / s-60m / s, and the stirring time is 10min-30min; in the third stage, the treatment temperature is 90°C-120°C, the stirring linear speed is 60m / s-70m / s, and the stirring time is 60min-120min; The preset rate is 10°C / min-15°C / min, and the target temperature is 25°C-40°C; During the cooling process, pulse shearing is applied, wherein one pulse shearing comprises shearing at 8 m / s-10 m / s for 4 s-6 s and shearing at 3 m / s-5 m / s for 8 s-12 s.

12. An all-solid-state lithium-ion battery, characterized in that: At least: Positive electrode; A negative electrode sheet, selected from the dry-process negative electrode sheet according to any one of claims 1 to 6, or a dry-process negative electrode sheet obtained by the preparation method according to any one of claims 7 to 11; The solid electrolyte layer is arranged between the positive electrode sheet and the negative electrode sheet.

13. The all-solid-state lithium-ion battery according to claim 12, characterized in that: The negative electrode plate further includes a solid electrolyte, which is selected from at least one of an oxide solid electrolyte, a sulfide solid electrolyte, and a halide solid electrolyte.

14. An electronic device, characterized in that: An all-solid-state lithium-ion battery comprising the all-solid-state lithium-ion battery according to any one of claims 12 to 13.

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