Composite negative electrode material, preparation method thereof and solid-state battery

Abstract

The invention relates to a composite negative electrode material and a preparation method thereof and a solid-state battery, the composite negative electrode material comprises a negative electrode active material and a sulfide solid-state electrolyte layer coating the surface of the negative electrode active material, and the negative electrode active material is selected from at least one of lithium titanium oxide or modified lithium titanium oxide; wherein a lithium sulfide with a chemical general formula of Li2Sx is formed on a contact interface of the negative electrode active material and the sulfide solid electrolyte layer, x is any integer selected from 1-8, and the lithium sulfide is at least partially embedded into the negative electrode active material and / or the sulfide solid electrolyte layer, and the specific surface area of the composite negative electrode material is less than or equal to 3.99 m < 2 > / g. The sulfide solid electrolyte layer is constructed on the surface of the negative electrode active material, and the lithium sulfide material with relatively high electronic conductivity is formed at the contact interface of the sulfide solid electrolyte layer and the negative electrode active material, so that the electrochemical performance and the service life of the solid-state battery are effectively improved.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a composite negative electrode material, its preparation method, and a solid-state battery. Background Technology

[0002] Sulfide solid electrolytes (LPSCs) have up to 10 -2 With an ionic conductivity of S / cm, solid-state batteries constructed by combining lithium titanate anode materials can combine the advantages of high energy density and excellent electrochemical performance. Summary of the Invention

[0003] Because the lithium titanate anode material and the sulfide solid electrolyte have a solid-solid contact, poor physical contact can easily lead to increased interfacial impedance, which limits ion transport efficiency. In addition, the lithium titanate anode material is prone to chemical side reactions with the sulfide solid electrolyte at the contact interface, generating a high-impedance interfacial layer, which further aggravates the interfacial impedance and affects the electrochemical performance and lifespan of the solid-state battery.

[0004] Therefore, it is necessary to address the above problems by providing a composite anode material, its preparation method, and a solid-state battery. By constructing a sulfide solid electrolyte layer on the surface of the anode active material, a lithium sulfide material with high electronic conductivity is formed at the interface between the two, thereby effectively improving the electrochemical performance and lifespan of the solid-state battery.

[0005] A composite negative electrode material includes a negative electrode active material and a sulfide solid electrolyte layer coated on the surface of the negative electrode active material, wherein the negative electrode active material is selected from at least one of lithium titanium oxide or modified lithium titanium oxide.

[0006] The interface between the negative electrode active material and the sulfide solid electrolyte layer forms a chemical formula of Li₂S. x The lithium sulfide, where x is selected from any integer from 1 to 8, is at least partially embedded in the negative electrode active material and / or the sulfide solid electrolyte layer, and the specific surface area of ​​the composite negative electrode material is less than or equal to 3.99 m². 2 / g.

[0007] In one embodiment, the specific surface area of ​​the coated composite anode material is reduced by 10% to 25% compared to the anode active material.

[0008] In one embodiment, the lithium sulfide in the composite anode material has a mass fraction of 0.1‰ to 0.5‰.

[0009] In one embodiment, the sulfide solid electrolyte layer is island-shaped and covers the surface of the negative electrode active material.

[0010] In one embodiment, the median particle size D of the sulfide solid electrolyte particles in the sulfide solid electrolyte layer is... 50 The range is from 0.1 μm to 10 μm;

[0011] And / or, the median particle size D of the negative electrode active material 50 The range is from 0.1 μm to 2.0 μm.

[0012] In one embodiment, the specific surface area of ​​the composite negative electrode material is 3.00 m². 2 / g~3.99 m 2 / g.

[0013] In one embodiment, the specific surface area of ​​the composite negative electrode material is 3.20 m². 2 / g~3.60 m 2 / g.

[0014] In one embodiment, the mass ratio of the negative electrode active material to the sulfide solid electrolyte layer is (1:0.001) to (1:0.050).

[0015] In one embodiment, the lithium titanium oxide is selected from Li4Ti5O. 12 Li7Ti5O 12 At least one of Li2TiO3, Li2Ti3O7 or LiTiO2.

[0016] In one embodiment, the modified lithium titanium oxide has the general chemical formula Li₄Ti. 5-x M x O 12 Where 0 < x < 1, and M is selected from at least one of magnesium, aluminum, manganese, iron or cobalt.

[0017] In one embodiment, the sulfide solid electrolyte layer uses a sulfide solid electrolyte with the general chemical formula Li. (7-a-b) PS (6-a-b) X a Y b Where X is at least one of fluorine, chlorine, bromine or iodine, Y is at least one of oxygen, indium, selenium, gallium, tellurium or germanium, and 0≤a+b≤2.

[0018] A method for preparing the composite anode material includes: mixing an anode active material with a sulfide solid electrolyte, subjecting it to heat treatment, and coating the surface of the anode active material with a sulfide solid electrolyte layer to obtain the composite anode material.

[0019] The negative electrode active material is selected from at least one of lithium titanium oxide or modified lithium titanium oxide, and the interface between the negative electrode active material and the sulfide solid electrolyte layer has the chemical formula Li₂S. x The lithium sulfide, where x is selected from any integer from 1 to 8, is at least partially embedded in the negative electrode active material and / or the sulfide solid electrolyte layer, and the specific surface area of ​​the composite negative electrode material is less than or equal to 3.99 m². 2 / g.

[0020] In one embodiment, the sulfide solid electrolyte layer is island-shaped and covers the surface of the negative electrode active material.

[0021] In one embodiment, the heat treatment temperature is 200°C to 500°C, and the time is 1 h to 20 h.

[0022] In one embodiment, the median particle size D of the negative electrode active material 50 The range is 0.1 μm to 2 μm;

[0023] And / or, the median particle size D of the sulfide solid electrolyte particles in the sulfide solid electrolyte layer. 50 The range is 0.1 μm to 10 μm.

[0024] In one embodiment, the mass ratio of the negative electrode active material to the sulfide solid electrolyte is (1:0.001) to (1:0.050).

[0025] A negative electrode includes a negative electrode active material layer, wherein the negative electrode active material layer includes the composite negative electrode material.

[0026] A solid-state battery, the solid-state battery including the negative electrode.

[0027] This application achieves a specific surface area of ​​3.99 m² by constructing a sulfide solid electrolyte layer on the surface of the negative electrode active material and controlling the interface structure. 2 The composite anode material with a density below / g achieves effective surface coverage and interface modification of the anode active material, reducing interfacial side reactions and thus improving the ionic conductivity of the composite anode material and enhancing the electrochemical performance of the battery. Furthermore, a lithium sulfide with high electronic conductivity is formed between the anode active material and the sulfide solid electrolyte layer, effectively improving the electronic conductivity of the composite anode material and further synergistically improving the ionic conductivity, thereby further enhancing the rate performance and cycle life of the battery. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is the XPS spectrum of the composite anode material prepared in Example 1 of this application. Detailed Implementation

[0030] To facilitate understanding of this application, it will be described in more detail below. However, it should be understood that this application can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular implementations or embodiments only and is not intended to be limiting of this application. The optional range of the term "and / or" as used herein includes any one of two or more of the related listed items, as well as any and all combinations of the related listed items, including any two related listed items, any more related listed items, or a combination of all related listed items.

[0032] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0033] The composite anode material provided in this application includes an anode active material and a sulfide solid electrolyte layer coated on the surface of the anode active material. The anode active material is selected from at least one of lithium titanium oxide or modified lithium titanium oxide. The interface between the anode active material and the sulfide solid electrolyte layer has a chemical formula of Li₂S. xThe lithium sulfide, where x is selected from any integer from 1 to 8, is at least partially embedded in the negative electrode active material and / or the sulfide solid electrolyte layer, and the specific surface area of ​​the composite negative electrode material is less than or equal to 3.99 m². 2 / g.

[0034] This application achieves a specific surface area of ​​3.99 m² by constructing a sulfide solid electrolyte layer on the surface of the negative electrode active material and controlling the interface structure. 2 Composite anode materials with a density of less than 1 g achieve effective coverage and interface modification of the surface of the anode active material, thereby improving the ionic conductivity of the composite anode material and enhancing the electrochemical performance of the battery.

[0035] Meanwhile, the lithium sulfide located at the interface between the negative electrode active material and the sulfide solid electrolyte layer has high electronic conductivity, which can effectively improve the electronic conductivity of the composite negative electrode material and further synergistically improve the ionic conductivity of the material with the sulfide solid electrolyte layer, thus forming an ion-electron dual-pathway conduction system. In addition, the coated sulfide solid electrolyte layer can reduce interfacial side reactions and suppress interfacial impedance, thereby significantly improving the rate performance and cycle life of solid-state batteries.

[0036] To achieve interface modification while preserving the efficient ion transport capability of the negative electrode active material, the sulfide solid electrolyte layer can be coated onto the surface of the negative electrode active material in an island-like form. This structure, through the synergistic configuration of localized coverage and exposed areas, can both suppress interfacial side reactions and construct a local electron conduction network using the covered areas, and maintain direct and rapid ion transport pathways through the exposed areas. This enhances interfacial chemical stability while ensuring the effectiveness of ion transport kinetics, thereby improving ionic conductivity. Furthermore, the unique interfacial structure formed by the island-like coating helps to regulate charge distribution and transfer processes at the interface, further improving the rate performance and cycle life of the solid-state battery.

[0037] Furthermore, compared with the negative electrode active material, the specific surface area of ​​the coated composite negative electrode material is reduced by 10% to 25%, for example, any value or a range between 10%, 13%, 15%, 20%, 23% or 25% of the specific surface area.

[0038] To ensure effective coverage and interface modification of the anode active material surface while also considering the rationality of the ion transport path and the effective suppression of interfacial chemical side reactions, the specific surface area of ​​the composite anode material can be controlled at 3.00 m². 2 / g~3.99 m 2 Within the range of / g, further selection is made from 3.20 m 2 / g~3.60 m2 / g, for example, can be selected from 3.20 m 2 / g、3.30 m 2 / g, 3.40 m 2 / g, 3.50 m 2 / g or 3.60 m 2 Any point value in / g or any range of values ​​between the two.

[0039] In this way, we can avoid the problem of excessively thick coating layers that may hinder ion conduction due to excessively high specific surface area change rate, and also prevent excessive exposure of active surfaces that may lead to exacerbated interfacial chemical side reactions and deteriorated electrode processing performance due to excessively low specific surface area change rate. This will improve the electrochemical performance of solid-state batteries while optimizing interfacial transport and enhancing chemical stability.

[0040] Furthermore, by adopting an island-shaped coating distribution to control the specific surface area of ​​the composite anode material, it is possible to better achieve synergistic optimization of interface stability and ionic conductivity.

[0041] To ensure efficient ion transport and interfacial compatibility while balancing the electrochemical reaction kinetics of the anode active material and the stability of the electrode structure, the median particle size D of the anode active material can be adjusted. 50 The particle size is controlled within the range of 0.1 μm to 2 μm, and can be selected from any point or range between 0.1 μm, 0.4 μm, 0.8 μm, 1.2 μm, 1.6 μm, or 2 μm. This size range is beneficial for maintaining a reasonable ion solid-phase diffusion distance while controlling the specific surface area of ​​the composite anode material. In addition, combined with the surface island-like coating structure, this particle size range can further synergistically optimize the bulk ion transport, interfacial side reaction suppression, and mechanical stability of the material.

[0042] To control the coating effect, the median particle size D of the sulfide solid electrolyte particles in the sulfide solid electrolyte layer is... 50 The particle size can range from 0.1 μm to 10 μm; for example, the median particle size D... 50 It can be any point value among 0.1 μm, 0.5 μm, 1 μm, 2 μm, 4 μm, 6 μm, 8 μm or 10 μm, or a range of values ​​between any two.

[0043] To fully leverage the role of lithium sulfide, effectively enhancing electronic conductivity while synergistically optimizing ionic conductivity with the sulfide solid electrolyte layer, and simultaneously reducing interfacial impedance and suppressing side reactions, thereby improving the rate performance and cycle stability of solid-state batteries, the mass fraction of lithium sulfide in the composite anode material can be 0.1‰ to 0.5‰. For example, the mass fraction can be any value among 0.1‰, 0.2‰, 0.3‰, 0.4‰, or 0.5‰, or any value within a range of two.

[0044] To achieve sufficient interface modification while maintaining high energy density and structural integrity of the composite anode material, the mass ratio of the anode active material to the sulfide solid electrolyte layer can be controlled within the range of (1:0.001) to (1:0.050), specifically any value from 1:0.001, 1:0.010, 1:0.020, 1:0.030, 1:0.040, or 1:0.050, or any value between any two. This allows for effective coverage and interface modification of the anode active material surface through a sufficient amount of sulfide solid electrolyte layer, suppressing side reactions and constructing a localized ion-electron synergistic transport interface. It also avoids the decrease in the proportion of anode active material, the tortuous ion transport path, and the overall reduction in material energy density caused by excessive sulfide solid electrolyte layer. Furthermore, this ratio range can synergize with the island-like coating structure and the particle size of the anode active material, further optimizing the balance of ion conduction, interface stability, and mechanical strength in the composite anode material.

[0045] Furthermore, when the mass ratio of the negative electrode active material to the sulfide solid electrolyte layer is within this range, an appropriate amount of lithium sulfide can be formed. This prevents the amount of lithium sulfide formed from being too small, which would prevent the formation of a dense layered contact between the negative electrode active material and the sulfide solid electrolyte layer, further leading to poor interfacial contact, increased interfacial impedance, and weakened suppression of lithium dendrites. Conversely, it also prevents the formation of too much lithium sulfide, which could result in excessive high electronic conductivity products between the negative electrode active material and the sulfide solid electrolyte layer, further obstructing the ion pathway at the interface and affecting the rate performance of the battery.

[0046] Optionally, the lithium titanium oxide may be selected from Li4Ti5O 12 Li7Ti5O 12 At least one of Li₂TiO₃, Li₂Ti₃O₇, or LiTiO₂, wherein the modified lithium titanium oxide may be a transition metal modified lithium titanium oxide, and the general chemical formula of the modified lithium titanium oxide may be Li₄Ti 5-x M x O 12 Where 0 < x < 1, and M is selected from at least one of magnesium, aluminum, manganese, iron or cobalt.

[0047] Optionally, the sulfide solid electrolyte used in the sulfide solid electrolyte layer may have the general chemical formula Li. (7-a-b) PS (6-a-b) X a Y b Where X is at least one of fluorine, chlorine, bromine or iodine, Y is at least one of oxygen, indium, selenium, gallium, tellurium or germanium, and 0≤a+b≤2.

[0048] This application also provides a method for preparing the composite negative electrode material, comprising: mixing a negative electrode active material with a sulfide solid electrolyte, subjecting it to heat treatment, and coating the surface of the negative electrode active material with a sulfide solid electrolyte layer to obtain the composite negative electrode material; wherein, the negative electrode active material is selected from at least one of lithium titanium oxide or modified lithium titanium oxide, and the contact interface between the negative electrode active material and the sulfide solid electrolyte layer forms a chemical formula of Li2S. x The lithium sulfide, where x is selected from any integer from 1 to 8, is at least partially embedded in the negative electrode active material and / or the sulfide solid electrolyte layer, and the specific surface area of ​​the composite negative electrode material is less than or equal to 3.99 m². 2 / g.

[0049] This application employs a melt solid-phase coating process to prepare the composite anode material. This method can form a structurally controllable sulfide solid electrolyte layer on the surface of the anode active material by adjusting process parameters, thereby achieving precise control over the coating morphology and specific surface area of ​​the composite anode material. Simultaneously, this process promotes the formation of a tightly bonded interface between the sulfide solid electrolyte layer and the anode active material, and during heat treatment, lithium sulfides are generated in situ at the interface. These lithium sulfides have high electronic conductivity and can form an electron permeation network at the interface, improving the reaction kinetics of the anode active material and further enhancing the rate performance and cycle life of the solid-state battery.

[0050] To achieve effective melting and spreading of the sulfide solid electrolyte while avoiding excessive temperature leading to structural damage to the negative electrode active material or excessive interfacial reaction, the heat treatment temperature is 200℃~500℃, or can be any value or a range between 200℃, 250℃, 300℃, 350℃, 400℃, 450℃ or 500℃. The heat treatment time is preferably 1 h~20 h, or can be any value or a range between 1 h, 5 h, 10 h, 15 h or 20 h.

[0051] By controlling the heat treatment temperature, the performance of composite anode materials and the formation of lithium sulfides can be regulated. When the heat treatment temperature is too high, the generated coating layer may decompose and deteriorate, which may lead to poor interfacial contact, obstruction of ion and electron transport paths, and the formation of a poor interfacial layer, which may further increase the interfacial impedance. In addition, at high temperatures, sulfide solid electrolytes are easy to decompose, which may make it difficult to form lithium sulfides at the interface, thereby affecting the cycle and rate performance of the battery.

[0052] Optionally, the median particle size D of the negative electrode active material 50 The particle size is 0.1 μm to 2 μm, and can be any value or a range between 0.1 μm, 0.4 μm, 0.8 μm, 1.2 μm, 1.6 μm, or 2 μm; the median particle size D of the sulfide solid electrolyte particles in the sulfide solid electrolyte layer is... 50 The thickness is 0.1 μm to 10 μm, and can be any value or a range between any two of 0.1 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm; the mass ratio of the negative electrode active material to the sulfide solid electrolyte is (1:0.001) to (1:0.050), for example, the mass ratio is any value or a range between any two of 1:0.001, 1:0.010, 1:0.020, 1:0.030, 1:0.040 or 1:0.050.

[0053] This application also provides a negative electrode, including a negative electrode active material layer, wherein the negative electrode active material layer includes the composite negative electrode material.

[0054] Optionally, the mass fraction of the composite negative electrode material in the negative electrode active material layer is 30% to 87%, for example, any one value or any two values ​​of 30%, 40%, 50%, 60%, 70%, 80% or 87%.

[0055] Optionally, the negative electrode active material further includes a solid electrolyte, wherein the mass fraction of the solid electrolyte in the negative electrode active material layer is 10% to 60%, for example, the mass ratio is any one value or any two values ​​of 10%, 20%, 30%, 40%, 50% or 60%; the solid electrolyte is selected from at least one of sulfide solid electrolyte, oxide solid electrolyte or polymer solid electrolyte.

[0056] Optionally, the negative electrode active material layer further includes a conductive agent, wherein the mass fraction of the conductive agent in the negative electrode active material layer is 0.5% to 10.0%, for example, any one value or a range of any two values ​​from 0.5%, 0.6%, 0.8%, 1.0%, 2.0%, 4.0%, 6.0%, 8.0%, and 10.0%; the conductive agent is selected from at least one of SP, KS6, SFG, VGCF, and CNT.

[0057] Optionally, the negative electrode active material layer further includes a binder, wherein the mass fraction of the binder in the negative electrode active material layer is 1.3% to 10.0%, for example, any one value or any two values ​​from 1.3%, 1.6%, 1.8%, 2.0%, 4.0%, 6.0%, 8.0%, and 10.0% by mass; the binder is selected from at least one of polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), nitrile rubber (NBR), and their modified materials.

[0058] Optionally, the negative electrode active material layer further includes a polymer additive, wherein the polymer additive has a mass fraction of 0.5% to 5% in the negative electrode active material layer, for example, a mass ratio of any one value or any two values ​​from 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, or 5.0%; the polymer additive is selected from at least one of polyethylene oxide (PEO), polyethylene glycol (PEG), or succinic anhydride (SN).

[0059] This application also provides a solid-state battery, which includes the aforementioned negative electrode.

[0060] Furthermore, the solid-state battery also includes a positive electrode, wherein the positive electrode active material is selected from high-nickel ternary lithium positive electrode materials. By using the positive electrode of this positive electrode active material in combination with the negative electrode of this application, the solid-state battery can have excellent electrochemical performance.

[0061] The technical solution of this application will be further described below through specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0062] Example 1

[0063] Preparation of composite anode material: Taking the median particle size D 50 Li4Ti5O with a thickness of 1 μm 12 A total of 100g of Li4Ti5O was added.12 Compared with the median particle size D of 1g 50 The composite anode material was obtained by uniformly mixing 2 μm Li6PS5Cl and calcining it at 350℃ for 10 h. In the composite anode material, the sulfide solid electrolyte layer is island-shaped and coated on Li4Ti5O. 12 surface.

[0064] Preparation of the negative electrode: 6.50g of composite negative electrode material, 2.95g of Li6PS5Cl solid electrolyte, 0.10g of SP conductive agent, 0.20g of CNT conductive agent, 0.20g of SBR binder, and 0.05g of SN polymer additive were placed in 10.00g of xylene and stirred evenly to obtain a negative electrode slurry. The slurry was then evenly coated on one side of an aluminum foil and dried to obtain the negative electrode.

[0065] Example 2

[0066] Preparation of composite anode material: Taking the median particle size D 50 Li7Ti5O with a thickness of 0.1 μm 12 A total of 100g of Li7Ti5O 12 With a median particle size D of 0.1g 50 Li6PS5Cl with a particle size of 0.1 μm 0.5 Br 0.5 After uniform mixing, the mixture was calcined at 200℃ for 20 h to obtain a composite anode material. In the composite anode material, the sulfide solid electrolyte layer was island-shaped and coated on Li7Ti5O. 12 surface.

[0067] Preparation of the negative electrode: 8.00g of composite negative electrode material and 1.75g ​​of Li6PS5Cl were prepared. 0.5 Br 0.5 Solid electrolyte, 0.05g SP conductive agent, 0.02g CNT conductive agent, 0.18g SBR binder, and 0.05g SN polymer additive are mixed evenly in 10.00g xylene to obtain a negative electrode slurry, which is then evenly coated on one side of an aluminum foil and dried to obtain the negative electrode.

[0068] Example 3

[0069] Preparation of composite anode material: Take the median particle size D 50 Li4Ti5O with a thickness of 2 μm 12 A total of 100g of Li4Ti5O was added. 12 Compared with the median particle size D of 5g 50 Li with a thickness of 10 μm 5.5 PS 4.5 Cl 1.5After uniform mixing, the mixture was calcined at 500℃ for 1 h to obtain a composite anode material. In the composite anode material, the sulfide solid electrolyte layer was island-shaped and coated on Li4Ti5O. 12 surface.

[0070] Preparation of the negative electrode: 5.50g of composite negative electrode material and 4.00g of Li were mixed. 5.5 PS 4.5 Cl 1.5 Solid electrolyte, 0.05g SP conductive agent, 0.01g CNT conductive agent, 0.25g SBR binder, and 0.10g SN polymer additive are mixed evenly in 10.00g xylene to obtain a negative electrode slurry, which is then evenly coated on one side of an aluminum foil and dried to obtain the negative electrode.

[0071] The negative electrode active material (Li4Ti5O) used in Example 1 12 The specific surface area of ​​the prepared composite anode material was measured. The instrument used for the measurement was a specific surface area and pore size analyzer (model: JW-BK400; manufacturer: Beijing Jingwei Gaobo Science and Technology Co., Ltd.). The measurement method was carried out in accordance with GB / T 19587-2017 "Determination of specific surface area of ​​solid materials by gas adsorption BET method". The formula for calculating the specific surface area change rate was: Change rate = (Specific surface area of ​​anode active material - Specific surface area of ​​composite anode material) / Specific surface area of ​​anode active material × 100%. The results are shown in Table 1.

[0072] Table 1

[0073]

[0074] The composite anode material prepared in Example 1 was tested using an X-ray photoelectron spectroscopy (XPS, model: ESCALAB Xi+, manufacturer: Thermo Fisher Scientific). The results are as follows: Figure 1 As shown, XPS test results show that a distinct lithium sulfide (Li2S) characteristic peak is obtained at S 2p, indicating that the composite anode material prepared in Example 1 contains Li2S.

[0075] The negative electrodes obtained in Examples 1-3 were sequentially stacked and pressed with a solid electrolyte membrane and a positive electrode to prepare a pouch solid-state battery. The solid electrolyte membrane was made of LPSC, and the positive electrode active material was NCM811. The dimensions of the pouch solid-state battery were as follows: positive electrode 43mm × 56mm, negative electrode 45mm × 58mm, and solid electrolyte membrane 47mm × 60mm. It should be noted that this application does not limit the type or amount of the solid electrolyte membrane active material and the positive electrode active material, nor does it limit the dimensions of the solid-state battery, as long as the requirements for solid-state battery fabrication and application are met.

[0076] The rate performance of the above-mentioned soft-pack solid-state battery was tested using the Landian Battery Testing System (model: CT3004A, manufacturer: Wuhan Landian Electronics Co., Ltd.). Specifically, the soft-pack solid-state battery was activated once at a current density of 0.05C at 45℃, and then charged and discharged three times at a current density of 1C. The results are shown in Table 2.

[0077] Table 2

[0078]

[0079] As can be seen from Table 2, the negative electrodes prepared in Examples 1-3 have good rate performance when used in pouch solid-state batteries.

[0080] The pouch solid-state batteries assembled in Examples 1-3 were subjected to charge-discharge cycle tests using the Landian Battery Testing System (model: CT3004A, manufacturer: Wuhan Landian Electronics Co., Ltd.). Specifically, the pouch solid-state batteries were charged and discharged once at 45°C with a current density of 0.05C and a voltage range of 2.5V to 4.2V to activate the batteries. Then, 200 charge-discharge cycle tests were performed within the same voltage range with a current density of 1C. The results are shown in Table 3.

[0081] Table 3

[0082]

[0083] The electrochemical impedance of the pouch solid-state battery was tested using an electrochemical workstation (model: CHI660E, manufacturer: Shanghai Chenhua Instrument Co., Ltd.). Specifically, EIS (electrochemical impedance spectroscopy) was performed in the frequency range of 1MHz to 0.1Hz under the condition of AC voltage amplitude of 5mV. The impedance data of the pouch solid-state battery were obtained, and the results are shown in Table 4.

[0084] Table 4

[0085]

[0086] As can be seen from the above data, by coating the surface of the negative electrode active material with a sulfide solid electrolyte layer, a specific amount of lithium sulfide is formed at the contact interface between the two. This lithium sulfide has high electronic conductivity, which can reduce side reactions at the contact interface and reduce interface impedance. While improving electronic conductivity, it also synergistically improves the ionic conductivity of the material, further enhancing the rate performance and cycle life of the solid-state battery.

[0087] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0088] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A composite negative electrode material, characterized in that, It includes a negative electrode active material and a sulfide solid electrolyte layer coated on the surface of the negative electrode active material, wherein the negative electrode active material is selected from at least one of lithium titanium oxide or modified lithium titanium oxide; The interface between the negative electrode active material and the sulfide solid electrolyte layer forms a chemical formula of Li₂S. x The lithium sulfide, where x is selected from any integer from 1 to 8, is at least partially embedded in the negative electrode active material and / or the sulfide solid electrolyte layer, and the specific surface area of ​​the composite negative electrode material is less than or equal to 3.99 m². 2 / g.

2. The composite negative electrode material according to claim 1, characterized in that, Compared with the aforementioned negative electrode active material, the specific surface area of ​​the coated composite negative electrode material is reduced by 10% to 25%.

3. The composite negative electrode material according to claim 1, characterized in that, The mass fraction of the lithium sulfide in the composite anode material is 0.1‰ to 0.5‰.

4. The composite negative electrode material according to claim 1, characterized in that, The sulfide solid electrolyte layer is island-shaped and covers the surface of the negative electrode active material.

5. The composite negative electrode material according to claim 1, characterized in that, The median particle size D of the sulfide solid electrolyte particles in the sulfide solid electrolyte layer 50 The range is from 0.1 μm to 10 μm; And / or, the median particle size D of the negative electrode active material 50 The range is from 0.1 μm to 2.0 μm.

6. The composite negative electrode material according to claim 1, characterized in that, The specific surface area of ​​the composite negative electrode material is 3.00 m². 2 / g~3.99 m 2 / g.

7. The composite negative electrode material according to claim 6, characterized in that, The specific surface area of ​​the composite negative electrode material is 3.20 m². 2 / g~3.60 m 2 / g.

8. The composite negative electrode material according to claim 1, characterized in that, The mass ratio of the negative electrode active material to the sulfide solid electrolyte layer is (1:0.001) to (1:0.050).

9. The composite negative electrode material according to claim 1, characterized in that, The lithium titanium oxide is selected from Li4Ti5O 12 Li7Ti5O 12 At least one of Li2TiO3, Li2Ti3O7 or LiTiO2.

10. The composite negative electrode material according to claim 1, characterized in that, The chemical formula of the modified lithium titanium oxide is Li₄Ti. 5-x M x O 12 Where 0 < x < 1, and M is selected from at least one of magnesium, aluminum, manganese, iron or cobalt.

11. The composite negative electrode material according to claim 1, characterized in that, The sulfide solid electrolyte layer uses a sulfide solid electrolyte with the general chemical formula Li. (7-a-b) PS (6-a-b) X a Y b Where X is at least one of fluorine, chlorine, bromine or iodine, Y is at least one of oxygen, indium, selenium, gallium, tellurium or germanium, and 0≤a+b≤2.

12. A method for preparing a composite negative electrode material as described in any one of claims 1 to 11, characterized in that, include: A composite anode material is obtained by mixing a negative electrode active material with a sulfide solid electrolyte, followed by heat treatment, and then coating the surface of the negative electrode active material with a sulfide solid electrolyte layer. The negative electrode active material is selected from at least one of lithium titanium oxide or modified lithium titanium oxide, and the interface between the negative electrode active material and the sulfide solid electrolyte layer has the chemical formula Li₂S. x The lithium sulfide, where x is selected from any integer from 1 to 8, is at least partially embedded in the negative electrode active material and / or the sulfide solid electrolyte layer, and the specific surface area of ​​the composite negative electrode material is less than or equal to 3.99 m². 2 / g.

13. The method for preparing the composite negative electrode material according to claim 12, characterized in that, The sulfide solid electrolyte layer is island-shaped and covers the surface of the negative electrode active material.

14. The method for preparing the composite negative electrode material according to claim 12, characterized in that, The heat treatment temperature is 200℃~500℃, and the time is 1 h~20 h.

15. The method for preparing the composite negative electrode material according to claim 12, characterized in that, The median particle size D of the negative electrode active material 50 The range is 0.1 μm to 2 μm; And / or, the median particle size D of the sulfide solid electrolyte particles in the sulfide solid electrolyte layer. 50 The range is from 0.1 μm to 10 μm.

16. The method for preparing the composite negative electrode material according to claim 12, characterized in that, The mass ratio of the negative electrode active material to the sulfide solid electrolyte is (1:0.001) to (1:0.050).

17. A negative electrode, characterized in that, It includes a negative electrode active material layer, wherein the negative electrode active material layer includes the composite negative electrode material according to any one of claims 1 to 11.

18. A solid-state battery, characterized in that, The solid-state battery includes the negative electrode as described in claim 17.

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