A modified silicon-based anode active material, its preparation method and application

Abstract

This invention provides a modified silicon-based anode active material, its preparation method, and its application. The modified silicon-based anode active material includes a silicon-based anode material and a polymer coating layer disposed on the surface of the silicon-based anode material. The polymer coating layer is formed through a water-soluble polymer heat treatment reaction. During the preparation of the anode slurry, the unreacted portion of the polymer coating layer dissolves in water and detaches, while the portion that reacts during heat treatment loses its water solubility and remains stably coated on the surface of the silicon-based anode material. This results in a porous network coating structure on the surface of the silicon-based anode material, effectively mitigating the volume expansion of the silicon-based anode material during charge and discharge, and giving the modified silicon-based anode active material excellent cycle performance. Simultaneously, due to the network structure of the polymer coating layer on the surface of the silicon-based anode material, a large number of conductive channels exist on its surface, preventing an increase in impedance and resulting in excellent conductivity, capacity, and rate performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery materials, and particularly relates to a modified silicon-based negative electrode active material and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of economy and technology, energy and environmental problems are becoming increasingly serious, and lithium ion batteries, as an important pillar of the new energy industry, have attracted much attention. In order to meet the performance requirements of mobile electronic products such as mobile phones, electric vehicle industry and other cyclic energy systems, it is imperative to develop lithium ion batteries with higher performance; the range anxiety of electric vehicles and the lightweight of consumer mobile electronic products such as mobile phones all require lithium ion batteries to pursue higher energy density.

[0003] Lithium ion batteries are usually assembled by a positive electrode, a negative electrode, a separator and an electrolyte, and the performance of the positive and negative electrode materials directly affects the quality of the lithium ion battery. The current commercial negative electrode material is mainly graphite, which has good cycle stability and conductivity, and the layered structure of graphite provides suitable lithium intercalation space, but the theoretical specific capacity of graphite is low (372 mAh / g), and the specific capacity of graphite as a negative electrode material has approached the theoretical value, and it is difficult to further improve, so there is an urgent need for negative electrode active materials with higher specific energy to meet the performance requirements of high-performance lithium ion batteries.

[0004] The theoretical specific capacity of silicon-based materials can reach 3580 mAh / g, and with the characteristics of extremely high specific capacity, low lithium extraction potential, abundant reserves and non-toxicity, silicon-based materials have become the recognized next-generation negative electrode material. However, silicon-based materials have a huge volume expansion (about 400%) during the cycle process, and the SEI film is unstable and has low conductivity, which limits its application.

[0005] To make up for the performance defects of silicon-based materials, researchers use carbon materials to coat or dope silicon-based materials. For example, CN108091848A discloses a carbon-coated mesoporous silicon-based negative electrode material, and the preparation method comprises the following steps: taking cetyltrimethylammonium bromide, octadecyl dimethyl benzyl quaternary ammonium chloride and the like as a template agent 1, dissolving it in an alcohol organic solvent, stirring thoroughly, and then performing crystallization treatment at 90-140°C for 2-6h to obtain a crystalline mixed solution A; taking ethylene oxide-propylene oxide-ethylene oxide triblock copolymer, polyoxyethylene ether of alkyl phenol, fatty alcohol polyoxyethylene ether and the like as a template agent 2, dissolving it in hydrochloric acid, adding a silicon source, and stirring uniformly to obtain a mixed solution B; adding the crystalline mixed solution A into the mixed solution B under stirring, mixing uniformly, and then performing crystallization, filtration, washing, drying, and calcination at 500-700°C for 5-7h to obtain the mesoporous silicon-based negative electrode material; in the material, the carbon coating layer formed by calcination can avoid the agglomeration of the material and buffer the expansion, and solve the problem of rapid capacity attenuation. CN114464785A discloses a carbon-coated silicon monoxide negative electrode material, and the preparation method comprises the following steps: first, depositing carbon on the surface of silicon monoxide by a low-temperature CVD gas phase method, and then performing high-temperature disproportionation to obtain the carbon-coated silicon monoxide negative electrode material; the method adopts the process of low-temperature coating and high-temperature disproportionation, so that the gap between the silicon monoxide matrix and the carbon layer can buffer the volume expansion of the material, thereby improving the volume expansion problem of the material during charging and discharging. CN109638265A discloses the preparation of a mesoporous carbon-coated silicon negative electrode material, which comprises the following steps: first, ultrasonic dispersion of nano-silicon powder, addition of tetraethyl orthosilicate and octadecyl trimethoxysilane, room temperature stirring, centrifugation, and calcination to obtain nano-silicon coated with mesoporous silicon on the surface; then, taking the mesoporous silicon-coated nano-silicon as a template, adding a carbon source and an organic solvent, mixing, and then calcining to carbonize the carbon source to obtain a composite powder of mesoporous carbon-coated silicon; and then washing the composite powder in HF to remove mesoporous silicon and silicon oxide, and drying to obtain the mesoporous carbon-coated silicon negative electrode material, which has better cycle and rate performance compared with conventional silicon-based materials. In general, the carbon-coated silicon-based material combines the performance advantages of carbon and silicon, and obtains a negative electrode active material with better performance than pure silicon-based materials; however, the carbon coating layer formed by high-temperature carbonization lacks ductility, and cannot effectively absorb or digest the tension generated by the volume expansion of the silicon-based material during battery charging and discharging, making it difficult to delay and prevent the pulverization of the negative electrode material. The volume expansion problem of the silicon-based material has not been completely and effectively solved, resulting in poor cycle performance and reliability of the lithium ion battery.

[0006] Therefore, it is a research focus in the field to develop silicon-based negative electrode materials with more excellent performance to improve the cycle performance of lithium ion batteries. SUMMARY

[0007] In view of the deficiencies of the prior art, the present application aims to provide a modified silicon-based negative electrode active material and a preparation method and application thereof, by arranging a polymer coating layer made of a specific material on the surface of the silicon-based negative electrode material, the volume expansion of the silicon-based negative electrode material can be effectively inhibited, and the impedance will not increase, so that the modified silicon-based negative electrode active material is used in a lithium ion battery, and the cycle performance of the battery is significantly improved.

[0008] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0009] In a first aspect, the present application provides a modified silicon-based negative electrode active material, which comprises a silicon-based negative electrode material and a polymer coating layer arranged on the surface of the silicon-based negative electrode material, and the polymer coating layer is formed by a water-soluble polymer heat treatment reaction.

[0010] In the modified silicon-based negative electrode active material provided by the present application, a specific polymer coating layer is arranged on the surface of the silicon-based negative electrode material, the raw material of the polymer coating layer is a water-soluble polymer, and the water-soluble polymer loses water solubility in the chemical reaction during the heat treatment process. Specifically, the water-soluble polymer is first uniformly coated on the surface of the silicon-based negative electrode material, and in the process of heat treatment, the part of the water-soluble polymer that has undergone chemical reaction loses water solubility (insoluble in water), while the part that has not undergone chemical reaction can still be dissolved in water. In the preparation process of the negative electrode slurry, the part of the polymer coating layer of the modified silicon-based negative electrode active material that has not undergone chemical reaction is dissolved in water (the solvent of the negative electrode slurry) and falls off, and the part that has undergone chemical reaction loses water solubility and is still stably coated on the surface of the silicon-based negative electrode material, so that a porous network-like coating structure mainly formed by the non-water-soluble polymer formed by the water-soluble polymer heat treatment reaction is formed on the surface of the silicon-based negative electrode material, effectively relieving the volume expansion of the silicon-based negative electrode material during the charging and discharging process, preventing material pulverization and falling off, and making the modified silicon-based negative electrode active material have excellent cycle performance. At the same time, since the polymer coating layer on the surface of the modified silicon-based negative electrode active material is a network structure, there are still a large number of conductive channels on the surface of the silicon-based negative electrode material, which will not cause an increase in the impedance of the material, so that the material has excellent conductivity and rate performance.

[0011] It should be noted that the coating of the polymer coating layer on the silicon-based negative electrode material includes complete coating or partial coating.

[0012] Preferably, the solubility of the water-soluble polymer in water is ≥1g / 100g, that is, the mass of the water-soluble polymer that can be dissolved in 100g of water is ≥1g.

[0013] Preferably, the molecular structure of the water-soluble polymer includes a hydrophilic group.

[0014] It should be noted that the water-soluble polymer is subjected to a chemical reaction in the heat treatment, so that the water-solubility of the polymer coating layer formed is significantly reduced compared to the original water-soluble polymer, but not completely lost; that is, not all hydrophilic groups in the water-soluble polymer are reacted, the part that has been chemically reacted is not soluble in water, and the part that has not been chemically reacted is still soluble in water, which in turn causes the water-soluble part of the polymer coating layer to be detached when the modified silicon-based negative electrode active material is prepared into a negative electrode slurry, so that a porous network-shaped polymer coating layer is formed on the surface of the silicon-based negative electrode material.

[0015] Preferably, the hydrophilic group includes a hydroxyl group and / or a carboxyl group.

[0016] Preferably, the water-soluble polymer includes any one of polyvinyl alcohol, polyacrylic acid, polyacrylic acid salt, polymaleic acid, polyitaconic acid, poly(methyl vinyl ether co-maleic acid) or a combination of at least two of them.

[0017] In the present application, the polyvinyl alcohol includes unmodified polyvinyl alcohol and / or polyvinyl alcohol derivatives (such as carboxyl-modified polyvinyl alcohol); the polyacrylic acid includes unmodified polyacrylic acid and / or polyacrylic acid derivatives; the polyacrylic acid salt includes sodium polyacrylate, potassium polyacrylate, ammonium polyacrylate, lithium polyacrylate, sodium polyacrylate copolymer, etc.; the polymaleic acid includes unmodified polymaleic acid and / or polymaleic acid derivatives; the polyitaconic acid includes unmodified polyitaconic acid and / or polyitaconic acid derivatives.

[0018] Preferably, the water-soluble polymer is subjected to at least one of an oxidation reaction, a cross-linking reaction, and a decomposition reaction in the heat treatment.

[0019] Preferably, the temperature of the heat treatment is 80-300℃, for example, it can be 90℃, 100℃, 110℃, 130℃, 150℃, 170℃, 190℃, 200℃, 220℃, 250℃, or 280℃, and specific point values between the above-mentioned point values, limited by the length and for the sake of simplicity, the present application does not exhaustively list the specific point values included in the range, and further preferably 100-200℃.

[0020] As a preferred technical solution of the present application, the temperature of the heat treatment is 80-300℃, preferably 100-200℃, thereby causing the water-soluble polymer to undergo any one or a combination of at least two of the following: a suitable degree of oxidation reaction, cross-linking reaction, and slight decomposition reaction, to form a polymer coating layer partially soluble in water and partially insoluble in water. If the temperature of the heat treatment is too low, the water-soluble polymer cannot undergo a sufficient degree of chemical reaction, resulting in the polymer coating layer still having a relatively high water solubility, which is dissolved in water (the solvent of the negative electrode slurry is water) during the preparation of the negative electrode slurry and thus falls off, failing to form an effective coating and also failing to inhibit the volume expansion of the silicon-based negative electrode material. If the temperature of the heat treatment is too high, on the one hand, the polymer coating layer can completely lose water solubility, and the network structure cannot be formed in the negative electrode slurry due to the water-soluble part falling off, resulting in an increased impedance and affecting the capacity and rate performance of the lithium ion battery; on the other hand, the high heat treatment temperature can cause the water-soluble polymer to carbonize, causing the coating layer to lose the ductility characteristics of the polymer material, failing to well absorb or digest the tension generated by the volume expansion of the silicon-based negative electrode material, making it difficult to delay and prevent pulverization, and resulting in poor cycle performance of the battery.

[0021] Preferably, the time of the heat treatment is 30-90min, for example, it can be 40min, 50min, 60min, 70min, or 80min, and specific point values between the above-mentioned point values. Due to the limitation of the length and the consideration of simplicity, the present application will not exhaustively list the specific point values included in the range.

[0022] Preferably, the mass percentage content of the polymer coating layer in the modified silicon-based negative electrode active material is 1-10%, for example, it can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, or 9%, and specific point values between the above-mentioned point values. Due to the limitation of the length and the consideration of simplicity, the present application will not exhaustively list the specific point values included in the range.

[0023] Preferably, the silicon-based negative electrode material includes silicon oxide,

[0024] Preferably, the silicon oxide is SiOx, 0

[0025] In a second aspect, the present application provides a preparation method of the modified silicon-based negative electrode active material according to the first aspect, the preparation method comprising: mixing a silicon-based negative electrode material and a water-soluble polymer solution to obtain a slurry; and performing heat treatment on the slurry to obtain the modified silicon-based negative electrode active material.

[0026] Preferably, the solvent of the water-soluble polymer solution comprises water.

[0027] Preferably, the mass percentage of the water-soluble polymer in the water-soluble polymer solution is 1-20%, for example, it can be 2%, 5%, 8%, 10%, 12%, 15%, or 18%, and specific point values between the above-mentioned point values, limited by the length and for the sake of simplicity, the present application will not list the specific point values included in the range.

[0028] Preferably, the mass ratio of the water-soluble polymer to the silicon-based negative electrode material is 1:(5-99), for example, it can be 1:6, 1:8, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, 1:55, 1:60, 1:65, 1:70, 1:75, 1:80, 1:85, 1:90, or 1:95, etc., and specific point values between the above-mentioned point values, limited by the length and for the sake of simplicity, the present application will not list the specific point values included in the range.

[0029] Preferably, the mixing is carried out under stirring; so that the silicon-based negative electrode material and the water-soluble polymer solution are fully mixed and uniformly distributed, forming a uniform slurry.

[0030] Preferably, the stirring speed is 500-2000 rpm, for example, it can be 600 rpm, 800 rpm, 1000 rpm, 1200 rpm, 1500 rpm, or 1800 rpm, and specific point values between the above-mentioned point values, limited by the length and for the sake of simplicity, the present application will not list the specific point values included in the range.

[0031] Preferably, the stirring time is 1-60 min, for example, it can be 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, or 55 min, and specific point values between the above-mentioned point values, limited by the length and for the sake of simplicity, the present application will not list the specific point values included in the range.

[0032] Preferably, the heat treatment further comprises a kneading step before the heat treatment.

[0033] Preferably, the kneading is carried out in a kneading device. The process of kneading helps the water-soluble polymer to be uniformly distributed, spread and coated on the surface of the silicon-based negative electrode material.

[0034] Preferably, the rotation speed of the kneading is 100-300 rpm, for example, it can be 120 rpm, 150 rpm, 180 rpm, 200 rpm, 220 rpm, 250 rpm or 280 rpm, and the specific point values between the above-mentioned point values, limited to the length and for the sake of simplicity, the present application does not list the specific point values included in the range.

[0035] Preferably, the time of the kneading is 20-100 min, for example, it can be 30 min, 40 min, 50 min, 60 min, 70 min, 80 min or 90 min, and the specific point values between the above-mentioned point values, limited to the length and for the sake of simplicity, the present application does not list the specific point values included in the range.

[0036] Preferably, the temperature of the heat treatment is 80-300℃, for example, it can be 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 220℃, 250℃ or 280℃, and the specific point values between the above-mentioned point values, limited to the length and for the sake of simplicity, the present application does not list the specific point values included in the range, further preferably 100-200℃.

[0037] Preferably, the time of the heat treatment is 30-90 min, for example, it can be 40 min, 50 min, 60 min, 70 min or 80 min, and the specific point values between the above-mentioned point values, limited to the length and for the sake of simplicity, the present application does not list the specific point values included in the range.

[0038] Preferably, the heat treatment is carried out in an oven.

[0039] Preferably, the heat treatment further comprises the steps of crushing and optionally screening after the heat treatment is completed.

[0040] Preferably, the crushing is carried out in a ball mill.

[0041] Preferably, the preparation method specifically comprises the following steps:

[0042] (1) mixing the silicon-based negative electrode material and the water-soluble polymer solution uniformly to obtain a slurry; the solvent of the water-soluble polymer solution is water, wherein the mass percentage content of the water-soluble polymer is 1-20%;

[0043] (2) after the slurry obtained in step (1) is kneaded at a rotation speed of 100-300 rpm for 20-100 min, it is placed under the condition of 100-200℃ for heat treatment for 30-90 min, and the obtained product is optionally crushed and optionally screened to obtain the modified silicon-based negative electrode active material.

[0044] As a preferred technical solution of the present application, the preparation method of the modified silicon-based negative electrode active material is a "water phase coating and drying" method, that is, first, a silicon-based negative electrode material and a water-soluble polymer solution are mixed to form a slurry, then kneading is performed to make the water-soluble polymer uniformly coated on the surface of the silicon-based negative electrode material, and then the product after kneading is subjected to heat treatment to make the water-soluble polymer undergo cross-linking, oxidation or slight decomposition and other chemical reactions to form a polymer coating layer. In the subsequent preparation process of the negative electrode slurry, the part of the polymer coating layer that has not undergone chemical reactions is still dissolved in water, and the part that has undergone chemical reactions is not dissolved in water, thereby forming a porous network structure coating on the surface of the silicon-based negative electrode material; this specific coating structure can effectively alleviate the volume expansion of the silicon-based negative electrode material during the charging and discharging process, prevent the material from pulverizing and falling off, thereby making the negative electrode material have excellent cycle stability and endowing the lithium ion battery with excellent cycle performance; at the same time, since the coating layer of the polymer on the silicon-based negative electrode material is a network structure, there are still a large number of conductive channels on the surface of the material, which will not cause an increase in the impedance of the material, and the negative electrode material and the lithium ion battery have excellent capacity and rate performance.

[0045] In a third aspect, the present application provides a negative electrode material composition comprising the modified silicon-based negative electrode active material according to the first aspect.

[0046] Preferably, the negative electrode material composition comprises a combination of a negative electrode active material comprising the modified silicon-based negative electrode active material, a conductive agent, a binder and optionally a thickening agent.

[0047] Preferably, the negative electrode active material comprises the modified silicon-based negative electrode active material and optionally a carbon material, further preferably a combination of the modified silicon-based negative electrode active material and the carbon material.

[0048] Preferably, the carbon material comprises any one of or a combination of at least two of graphite, carbon black, carbon nanotubes, carbon fibers, mesocarbon microbeads or petroleum coke, further preferably graphite.

[0049] Preferably, the graphite is natural graphite and / or artificial graphite.

[0050] Preferably, the mass percentage content of the modified silicon-based negative electrode active material in the negative electrode active material is 1-50%, for example, it can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40% or 45%, and specific point values between the above point values, limited by the length and for the sake of simplicity, the present application will not exhaustively list the specific point values included in the range.

[0051] Preferably, the conductive agent comprises any one of or a combination of at least two of carbon black, graphite, carbon nanotubes or carbon fibers.

[0052] Preferably, the mass of the conductive agent is 0.1-5.0 parts, for example, 0.1 parts, 0.3 parts, 0.5 parts, 0.7 parts, 0.9 parts, 1.0 parts, 1.2 parts, 1.5 parts, 1.8 parts, 2.0 parts, 2.2 parts, 2.5 parts, 2.8 parts, 3.0 parts, 3.2 parts, 3.5 parts, 3.8 parts, 4.0 parts, 4.2 parts, 4.5 parts, or 4.8 parts, and specific point values between the above point values, to the mass of the negative active material being 100 parts, and the specific point values included in the range are not listed exhaustively in the present application due to the limitation of the length and for the sake of simplicity.

[0053] Preferably, the binder includes styrene-butadiene rubber (SBR).

[0054] Preferably, the mass of the binder is 0.1-5.0 parts, for example, 0.1 parts, 0.3 parts, 0.5 parts, 0.7 parts, 0.9 parts, 1.0 parts, 1.2 parts, 1.5 parts, 1.8 parts, 2.0 parts, 2.2 parts, 2.5 parts, 2.8 parts, 3.0 parts, 3.2 parts, 3.5 parts, 3.8 parts, 4.0 parts, 4.2 parts, 4.5 parts, or 4.8 parts, and specific point values between the above point values, to the mass of the negative active material being 100 parts, and the specific point values included in the range are not listed exhaustively in the present application due to the limitation of the length and for the sake of simplicity.

[0055] Preferably, the thickening agent includes sodium carboxymethyl cellulose (CMC).

[0056] Preferably, the mass of the thickening agent is 0.1-3.0 parts, for example, 0.1 parts, 0.3 parts, 0.5 parts, 0.7 parts, 0.9 parts, 1.0 parts, 1.2 parts, 1.5 parts, 1.8 parts, 2.0 parts, 2.2 parts, 2.5 parts, or 2.8 parts, and specific point values between the above point values, to the mass of the negative active material being 100 parts, and the specific point values included in the range are not listed exhaustively in the present application due to the limitation of the length and for the sake of simplicity.

[0057] In a fourth aspect, the present application provides a negative electrode sheet, which includes a current collector and a coating layer disposed on the current collector, and the material of the coating layer includes the negative material composition according to the third aspect.

[0058] Preferably, the method for preparing the negative electrode sheet includes: mixing the negative material composition with water uniformly to obtain a negative electrode slurry; and coating the negative electrode slurry on a current collector and drying to obtain the negative electrode sheet.

[0059] Preferably, the drying further includes a step of rolling.

[0060] In a fifth aspect, the present application provides an electrochemical energy storage device, comprising at least one of the modified silicon-based negative electrode active material according to the first aspect, the negative electrode material composition according to the third aspect, or the negative electrode sheet according to the fourth aspect.

[0061] Preferably, the electrochemical energy storage device comprises any one of a lithium ion battery, a sodium ion battery, a supercapacitor, a fuel cell, or a solar cell, further preferably a lithium ion battery.

[0062] Compared with the prior art, the present application has the following beneficial effects:

[0063] (1) In the modified silicon-based negative electrode active material provided by the present application, a specific polymer coating layer is arranged on the surface of the silicon-based negative electrode material, which is formed by a water-soluble polymer heat treatment reaction, and the water solubility of the water-soluble polymer is significantly reduced. In the preparation process of the negative electrode slurry, the unreacted part of the polymer coating layer dissolves in water and falls off, and the part that has reacted by heat treatment loses water solubility and remains stably coated on the surface of the silicon-based negative electrode material, so that a porous network-like coating structure is formed on the surface of the silicon-based negative electrode material, effectively relieving the volume expansion of the silicon-based negative electrode material during the charging and discharging process, preventing material pulverization and falling off, and making the modified silicon-based negative electrode active material have excellent cycle performance. At the same time, due to the network structure of the polymer coating layer on the surface of the silicon-based negative electrode material in the lithium ion battery, there are a large number of conductive channels on the surface, which will not cause an increase in impedance, and the lithium ion battery has excellent conductivity, capacity, and rate performance.

[0064] (2) The modified silicon-based negative electrode active material is used in the negative electrode sheet and the lithium ion battery, which significantly inhibits the volume expansion of the silicon-based material while having excellent conductivity, so that the capacity retention rate of the lithium ion battery is ≥93.9% after 100 cycles at room temperature, and the rate performance is ≥84.4%, which significantly improves the cycle performance of the lithium ion battery. DETAILED DESCRIPTION

[0065] The technical solutions of the present application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application, and should not be regarded as specific limitations on the present application.

[0066] As used herein, the terms "comprising", "including", "containing", "having" or any other similar forms are intended to cover non-exclusive inclusions. For example, a composition, step, method, article, or device that includes the listed elements does not necessarily limit those elements to only those elements explicitly listed, but can include other elements not expressly listed or inherent to such composition, step, method, article, or device.

[0067] "Optionally", "optionally" or "any one of" means that the matter or event described thereafter can or can not occur, and the description includes the case where the event occurs and the case where the event does not occur.

[0068] The indefinite articles "a" and "an" before an element or component of the application are not intended to be limiting of the quantity of such element or component to one unless the context clearly indicates otherwise. Thus, "a" or "an" can be read to include one or at least one, and the singular word form of an element or component can include the plural unless the context clearly indicates otherwise.

[0069] The terms "one embodiment", "some embodiments", "exemplary", "specific example" or "some examples" as described herein mean that a particular feature, structure, material or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the application. The appearances of the above terms in various places in the specification are not necessarily referring to the same embodiment or example.

[0070] Furthermore, the technical features involved in each embodiment of the application can be combined with each other as long as there is no conflict.

[0071] In the following specific embodiments of the application, the silicon-based negative electrode material and the water-soluble polymer used are all commercially available products. The silicon-based negative electrode material is silicon oxide (SiOx, purchased from Global Graphene Group, USA, model GA-K9C2), and the specific information of the water-soluble polymer is shown in Table 1:

[0072] Table 1

[0073] Water-soluble polymer Grade Manufacturer Polyvinyl alcohol 1799 Kuraray Polyvinyl alcohol 1788 Kuraray Carboxyl-modified polyvinyl alcohol SG181 Kuraray Polyacrylic acid P815683 M&K Sodium polyacrylate S818399 M&K Sodium polyacrylate copolymer A ONE Kenrich Polymaleic acid P823909 M&K Poly(methyl vinyl ether-co-maleic acid) P815417 M&K

[0074] Example 1

[0075] A modified silicon-based negative electrode active material and a preparation method thereof, the modified silicon-based negative electrode active material comprising a silicon-based negative electrode material (SiOx powder) and a polymer coating layer provided on the surface of the silicon-based negative electrode material, the polymer coating layer being formed by a polyvinyl alcohol 1799 heat treatment reaction.

[0076] The preparation method of the modified silicon-based negative electrode active material comprises: dissolving 5 g of polyvinyl alcohol 1799 in 100 g of water to prepare a polyvinyl alcohol aqueous solution; adding 95 g of SiOx powder to the polyvinyl alcohol aqueous solution under the condition of 1000 rpm stirring, and obtaining a uniform slurry after 30 min. The slurry is placed in a kneading device for kneading at 150 rpm for 1 h, then taken out and heat treated at 150°C for 60 min in an oven, and then pulverized by a ball mill to obtain the modified silicon-based negative electrode active material.

[0077] Examples 2-10

[0078] A modified silicon-based negative electrode active material and a preparation method thereof, which are only different from those of Example 1 in the type, amount of water-soluble polymer and parameters of heat treatment, as shown in Table 2; the types, amounts and parameters of materials not shown in Table 2 are the same as those of Example 1.

[0079] Table 2

[0080]

[0081] Comparative Example 1

[0082] The silicon-based negative electrode material is silicon oxide SiOx without treatment.

[0083] Comparative Example 2

[0084] A modified silicon-based negative electrode active material and a preparation method thereof, the modified silicon-based negative electrode active material comprising a silicon-based negative electrode material (SiOx powder) and a polymer coating layer arranged on the surface of the silicon-based negative electrode material, and the material of the polymer coating layer being polyvinyl alcohol 1799.

[0085] The preparation method of the modified silicon-based negative electrode active material comprises: dissolving 5 g of polyvinyl alcohol 1799 in 100 g of water to prepare a polyvinyl alcohol aqueous solution; adding 95 g of SiOx powder to the polyvinyl alcohol aqueous solution under the condition of 1000 rpm stirring, and obtaining a uniform slurry after 30 min. The slurry is placed in a kneading device for kneading at 150 rpm for 1 h, and then dried in a vacuum oven at 50℃ for 24 h, and finally pulverized by a ball mill to obtain the modified silicon-based negative electrode active material.

[0086] Comparative Example 3

[0087] A modified silicon-based negative electrode active material and a preparation method thereof, the modified silicon-based negative electrode active material comprising a silicon-based negative electrode material (SiOx powder) and a polymer coating layer arranged on the surface of the silicon-based negative electrode material, and the preparation method being as follows:

[0088] 5 g of polyvinylidene fluoride (PVDF, P822261, Macklin) is dissolved in 100 g of N-methyl pyrrolidone (NMP) to prepare a PVDF solution; 95 g of SiOx powder is added to the PVDF solution under the condition of 1000 rpm stirring, and a uniform slurry is obtained after 30 min. The slurry is placed in a kneading device for kneading at 150 rpm for 1 h, and then taken out and heat treated in an oven at 150℃ for 60 min, and finally pulverized by a ball mill to obtain the modified silicon-based negative electrode active material.

[0089] Application Examples 1-10, Comparative Application Examples 1-3

[0090] A negative electrode sheet, comprising a current collector (Cu foil) and a coating layer provided on the current collector, wherein the material of the coating layer is a negative electrode material composition; the negative electrode material composition comprises a silicon-based negative electrode active material, artificial graphite (Jiangxi Zichen G49), a conductive agent (conductive carbon black, SP), a binder (styrene-butadiene rubber, SBR) and a thickening agent (sodium carboxymethyl cellulose, CMC) in a mass ratio of 10:85:1.0:2.5:1.5; wherein the silicon-based negative electrode active material is the modified silicon-based negative electrode active material provided in any one of embodiments 1-10 or any one of comparative examples 1-3.

[0091] Preparation of the negative electrode sheet: the silicon-based negative electrode active material, artificial graphite, SP, SBR and CMC are mixed in a mass ratio of 10:85:1.0:2.5:1.5, and then added into deionized water in a proportion of 40wt% of the system solid content for fully stirring and mixing to form a uniform negative electrode slurry. After passing through a 100-mesh sieve, the slurry is coated on a negative electrode current collector Cu foil, dried, and then rolled using a roller at a unit length load of 10×10 4 N / m to obtain the negative electrode sheet.

[0092] A lithium ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the negative electrode sheet is the aforementioned negative electrode sheet; and the lithium ion battery is prepared as follows:

[0093] (1) Preparation of the positive electrode sheet: a positive electrode active material (lithium iron phosphate), a conductive agent (conductive carbon black) and a binder (polyvinylidene fluoride, PVDF) are mixed in a mass ratio of 95.5:2.0:2.5, and then added into N-methyl pyrrolidone (NMP) in a proportion of 50wt% of the system solid content for fully stirring and mixing to form a uniform positive electrode slurry. After passing through a 100-mesh sieve, the slurry is coated on a positive electrode current collector Al foil, dried, and then rolled using a roller at a unit length load of 10×10 4 N / m to obtain the positive electrode sheet.

[0094] (2) Preparation of the negative electrode sheet: as described above;

[0095] (3) Separator: a PE porous polymer film (Shenzhen Xingyuan Material Technology Co., Ltd.) is used as the separator;

[0096] (4) Assembly of the lithium ion battery: the positive electrode sheet, the separator and the negative electrode sheet are sequentially wound to obtain a battery cell; the battery cell is packaged with an aluminum plastic film, and after drying to remove water, an electrolyte is injected. After vacuum packaging, standing, formation, secondary sealing, shaping and other processes, the lithium ion battery is obtained.

[0097] Performance test:

[0098] (1) Normal temperature cycle performance

[0099] The lithium ion battery prepared above was charged at 0.33 C to 4.2 V, then charged at constant voltage to the cutoff current of 0.02 C, discharged at 0.33 C to 2.5 V, and then left for 5 min, and then charged at 0.33 C to 4.2 V, then charged at constant voltage to the cutoff current of 0.02 C, and discharged at 0.33 C to 2.5 V, so as to carry out initial adjustment.

[0100] The lithium ion battery after initial adjustment was charged at 0.5 C to 4.2 V at 25 ℃, then charged at constant voltage to the cutoff current of 0.02 C, left for 5 min, and then discharged at 1 C to 2.5 V, left for 5 min, and then the first cycle discharge capacity was measured; after 100 cycles of charging / discharging, the 100th cycle discharge capacity was measured, and the 100th cycle capacity retention rate was calculated by the following formula:

[0101] The capacity retention rate (%) after 100 cycles = 100% x the 100th cycle discharge capacity / the first cycle discharge capacity.

[0102] (2) Rate performance

[0103] The lithium ion battery after initial adjustment was charged at 0.5 C to 4.2 V at 25 ℃, then charged at constant voltage to the cutoff current of 0.02 C, left for 5 min, and then discharged at 1 C to 2.5 V, left for 5 min, and then the 1 C discharge capacity was measured. Then the battery was charged at 0.5 C to 4.2 V, then charged at constant voltage to the cutoff current of 0.02 C, left for 5 min, and then discharged at 3 C to 2.5 V, and the discharge capacity at 3 C rate was measured.

[0104] The 3 C capacity retention rate (%) = 100% x the 3 C discharge capacity / the 1 C discharge capacity.

[0105] The test results are shown in Table 3.

[0106] Table 3

[0107]

[0108]

[0109] According to the performance test data in Table 3, compared with the unmodified silicon oxide negative electrode material in Comparative Example 1, the modified silicon-based negative electrode active material provided in Examples 1-8 effectively alleviates the pulverization caused by the volume expansion of the silicon-based negative electrode material, has excellent structural stability and cycle performance, and makes the lithium ion battery containing the same have a capacity retention rate ≥ 93.9% after 100 cycles at room temperature, a rate performance ≥ 84.4%, and excellent cycle performance and rate performance.

[0110] In the present application, the surface of the silicon-based negative electrode material is provided with a specific polymer coating layer formed by a water-soluble polymer heat treatment reaction; in the preparation process of the negative electrode slurry, the unreacted part of the polymer coating layer is dissolved in water and falls off, and the part that has reacted loses water solubility and remains stably coated on the surface of the silicon-based negative electrode material, so that a porous network-like coating structure is formed on the surface of the silicon-based negative electrode material, effectively relieving the volume expansion of the silicon-based negative electrode material during charging and discharging, so that the modified silicon-based negative electrode active material has excellent cycle performance. At the same time, since the polymer coating layer on the surface of the silicon-based negative electrode material has a network structure, there are a large number of conductive channels on its surface, which will not cause an increase in impedance, and has excellent conductivity and rate performance. According to the preparation process and effect data of Examples 1-10, by adjusting the heat treatment conditions, the reaction degree of the water-soluble polymer can be controlled, and the cycle performance and rate performance of the modified silicon-based negative electrode active material and lithium ion battery can be optimized, but if the heat treatment temperature is too low (Example 9), the reaction of the water-soluble polymer is insufficient, a large amount of components in the polymer coating layer are dissolved in the negative electrode slurry, and the coating structure on the silicon-based material is too small to effectively relieve the volume expansion of the silicon-based material, resulting in a decrease in cycle performance; if the heat treatment temperature is too high (Example 10), the polymer coating layer completely loses water solubility, and the coating structure formed on the silicon-based material is too dense, resulting in a decrease in conductivity and an increase in impedance, which reduces the rate performance of the battery. The water-soluble polymer in Comparative Example 2 is not effectively heat treated, resulting in a large amount of polymer coating layer on the surface of the silicon-based negative electrode material being dissolved in the negative electrode slurry, and no effective coating being formed on the silicon-based material, so that the pulverization caused by volume expansion cannot be inhibited, resulting in poor cycle performance; and in Comparative Example 3, a non-water-soluble polymer is used to coat the silicon-based negative electrode material, and the polymer coating layer on the surface of the silicon-based material is very dense, which hinders the conductive channels, increases the impedance of the material, and greatly reduces the rate performance.

[0111] The applicant declares that the modified silicon-based negative electrode active material of the present application, its preparation method and application are illustrated by the above examples, but the present application is not limited to the above examples, i.e. it does not mean that the present application must rely on the above examples to be implemented. Those skilled in the art should understand that any improvement of the present application, equivalent replacement of each raw material of the product of the present application, addition of auxiliary ingredients, selection of specific methods, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A modified silicon-based negative electrode active material, characterized in that, The modified silicon-based negative electrode active material comprises a silicon-based negative electrode material and a polymer coating layer arranged on the surface of the silicon-based negative electrode material, and the polymer coating layer is formed by a water-soluble polymer heat treatment reaction; The temperature of the heat treatment is 100-200℃; The time of the heat treatment is 30-90 min; The water-soluble polymer is selected from any one or a combination of at least two of a polyvinyl alcohol derivative, a polyacrylate, a polymaleic acid, a polyitaconic acid, and a poly(methyl vinyl ether-co-maleic acid); When the negative electrode slurry is prepared, the water-soluble polymer coating layer is partially dissolved in water and falls off, forming a porous network coating structure on the surface of the silicon-based negative electrode material; The preparation method of the modified silicon-based negative electrode active material comprises: mixing a silicon-based negative electrode material and a water-soluble polymer solution to obtain a slurry; and performing heat treatment on the slurry to obtain the modified silicon-based negative electrode active material, wherein the mass ratio of the water-soluble polymer to the silicon-based negative electrode material is 1:(5-20).

2. The modified silicon-based negative electrode active material according to claim 1, characterized in that The water-soluble polymer undergoes at least one of an oxidation reaction, a cross-linking reaction, and a decomposition reaction in the heat treatment.

3. The modified silicon-based negative electrode active material according to claim 1 or 2, characterized in that The mass percentage of the polymer coating layer in the modified silicon-based negative electrode active material is 1-10%.

4. The modified silicon-based negative electrode active material according to claim 1 or 2, characterized in that, The silicon-based negative electrode material comprises silicon oxide.

5. The modified silicon-based negative electrode active material according to claim 4, characterized in that The silicon oxide is SiOx, and 0 6. A method for producing the modified silicon-based negative electrode active material according to any one of claims 1 to 5, characterized by, The preparation method comprises: mixing a silicon-based negative electrode material and a water-soluble polymer solution to obtain a slurry; and performing heat treatment on the slurry to obtain the modified silicon-based negative electrode active material; The temperature of the heat treatment is 80-300℃; The time of the heat treatment is 30-90 min; The mass ratio of the water-soluble polymer to the silicon-based negative electrode material is 1:(5-20).

7. The production method according to claim 6, wherein The solvent of the water-soluble polymer solution comprises water.

8. The production method according to claim 6 or 7, characterized by, The mass percentage of the water-soluble polymer in the water-soluble polymer solution is 1-20%.

9. The preparation method according to claim 6, characterized in that, The step of kneading is further included before the heat treatment.

10. The method of claim 9, wherein, The rotation speed of the kneading is 100-300 rpm.

11. The production method according to claim 9 or 10, characterized by, The time of the kneading is 20-100 min.

12. The method of claim 6, wherein, The temperature of the heat treatment is 100-200℃.

13. The production method according to claim 6 or 9, characterized by, A step of crushing is further included after the heat treatment is completed.

14. A negative electrode material composition, characterized by, The negative electrode material composition comprises the modified silicon-based negative electrode active material according to any one of claims 1-5.

15. The negative electrode material composition of claim 14, wherein, The negative electrode material composition comprises a combination of a negative electrode active material, a conductive agent, a binder, and optionally a thickening agent, and the negative electrode active material comprises the modified silicon-based negative electrode active material.

16. The negative electrode material composition of claim 15, wherein, The negative electrode active material comprises the modified silicon-based negative electrode active material and optionally a carbon material.

17. The negative electrode material composition of claim 16, wherein, The carbon material comprises any one or a combination of at least two of graphite, carbon black, carbon nanotubes, carbon fibers, mesocarbon microbeads, or petroleum coke.

18. The negative electrode material composition of claim 17, wherein, The graphite is natural graphite and / or artificial graphite.

19. A negative electrode sheet characterized by comprising: The negative electrode tab comprises a current collector and a coating layer arranged on the current collector, and the material of the coating layer comprises the negative electrode material composition according to any one of claims 14-18.

20. An electrochemical energy storage device, characterized by The electrochemical energy storage device comprises at least one of the modified silicon-based negative electrode active material according to any one of claims 1 to 5, the negative electrode material composition according to any one of claims 14 to 18, or the negative electrode sheet according to claim 19.

21. The electrochemical energy storage device of claim 20, wherein, The electrochemical energy storage device is any one of a lithium-ion battery, a sodium-ion battery, a supercapacitor, a fuel cell, or a solar cell.

22. The electrochemical energy storage device of claim 21, wherein, The electrochemical energy storage device is a lithium-ion battery.

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