Negative electrode sheet for solid-state battery and method for manufacturing the same, and battery

Abstract

This invention relates to the field of battery technology, specifically to a negative electrode sheet for solid-state batteries, its preparation method, and the battery itself. The disclosed negative electrode sheet for solid-state batteries includes: a current collector, and a coating disposed on at least one surface of the current collector in the thickness direction; the coating includes a silicon-based material, a sulfide electrolyte material, and carbon nanotubes; wherein the sulfide electrolyte material includes Li7P2S8I electrolyte. The negative electrode sheet of this invention has good ionic and electronic conductivity, effectively mitigating the volume expansion of the negative electrode sheet during cycling, and improving the battery's energy density, cycle performance, and fast-charging performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a negative electrode sheet for solid-state batteries, a method for preparing the same, and the battery itself. Background Technology

[0002] Silicon-based anode materials have high theoretical capacity, with a potential of E=0.3V (relative to Li). + The high lithium intercalation potential of ( / Li) also prevents lithium metal nucleation and dendrite growth. In solid-state batteries, due to the large volume expansion of silicon-based materials during cycling, silicon particles are easily crushed, causing some ionic and electronic conduction pathways of the negative electrode to fail, which in turn increases the internal resistance of the solid-state battery and reduces its fast-charging performance.

[0003] Therefore, it is of great significance to improve the strength of silicon-based anode sheets, reduce the volume expansion of silicon-based anode materials during cycling, improve the ionic and electronic conductivity of silicon-based anode sheets, and enable the anode sheets to have good fast-charging performance. Summary of the Invention

[0004] In view of this, the present invention aims to at least partially solve one of the technical problems in the related art. To this end, the present invention provides a negative electrode sheet for solid-state batteries, a method for preparing the same, and a battery. By adding carbon nanotubes and sulfide electrolyte materials to silicon-based materials, the ionic conductivity and electronic conductivity of the negative electrode sheet can be improved, effectively mitigating the volume expansion of the negative electrode sheet during cycling, giving the negative electrode sheet good strength, and thus improving the energy density, cycle performance, and fast-charging performance of the battery.

[0005] To solve the above-mentioned technical problems, the present invention is implemented as follows: According to one aspect of the present invention, a negative electrode sheet for a solid-state battery is provided, comprising: a current collector, and a coating disposed on at least one surface of the current collector in the thickness direction; The coating comprises silicon-based materials, sulfide electrolyte materials, and carbon nanotubes; The sulfide electrolyte material includes Li7P2S8I electrolyte.

[0006] According to a second aspect of the present invention, the present invention also provides a method for preparing a negative electrode sheet for a solid-state battery, comprising the following steps: Silicon-based materials, sulfide electrolyte materials, carbon nanotubes, and binders are added to a solvent, stirred, and ball-milled to obtain a slurry. The slurry is coated onto at least one side of the current collector surface in the thickness direction and dried to obtain the negative electrode sheet; wherein the sulfide electrolyte material includes Li7P2S8I electrolyte.

[0007] According to a third aspect of the present invention, the present invention also provides a battery comprising: a negative electrode sheet as described in any of the above embodiments, or a negative electrode sheet prepared by the preparation method described in any of the above embodiments.

[0008] Implementing the technical solution of the present invention has at least the following beneficial effects: 1. In this invention, by adding carbon nanotubes with a mass content of non-zero and sulfide electrolyte materials with a mass content of non-zero to silicon-based materials, the ionic conductivity and electronic conductivity of the negative electrode sheet can be improved, effectively alleviating the volume expansion of the negative electrode sheet during cycling, giving the negative electrode sheet good strength, and thus improving the energy density, cycle performance and fast charging performance of the battery.

[0009] 2. In a preferred embodiment of the present invention, the sulfide electrolyte material is Li7P2S8I electrolyte, which has a low Young's modulus and good contact with silicon-based materials, which can further alleviate the interface contact problem caused by silicon-based expansion; and when Li7P2S8I electrolyte is introduced into silicon-based materials to form a negative electrode sheet, a small amount of LiI will be generated during the formation, which acts as an SEI film, which can prevent the sulfide electrolyte and silicon-carbon materials from undergoing more side reactions, thereby ensuring that the battery has excellent cycle life.

[0010] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0011] The technical solution of the present invention and how the technical solution of the present invention solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of the present invention will be described below.

[0012] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0013] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0014] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0015] Silicon-based anode materials have high theoretical capacity, with a potential of E=0.3V (relative to Li). + The high lithium intercalation potential of silicon (Li) also prevents lithium metal nucleation and dendrite growth. In solid-state batteries, due to the large volume expansion effect of silicon anodes, silicon particles are pulverized during lithiation / delithiation, easily forming gaps between silicon and active materials and solid electrolytes. This ultimately leads to the failure of the ion-electron conduction pathway in the anode, severely affecting the lifespan of solid-state batteries.

[0016] Currently, the common method is to add additives to the silicon-based negative electrode to enhance its strength and prevent large volume expansion of the silicon-based material; however, this method can easily affect the fast-charging performance of the negative electrode.

[0017] In view of the above problems, how to obtain a negative electrode with good ionic and electronic conductivity, while also making the negative electrode have good fast charging performance, has become an important research topic.

[0018] The specific technical solution of the present invention is as follows: [Negative electrode sheet for solid-state batteries] In some embodiments of the present invention, a negative electrode sheet for a solid-state battery is provided, comprising: a current collector, and a coating disposed on at least one surface of the current collector in the thickness direction; The coating comprises silicon-based materials, sulfide electrolyte materials, and carbon nanotubes; among which, the sulfide electrolyte material includes Li7P2S8I electrolyte.

[0019] As an example, the current collector in the negative electrode is made of metal foil, such as aluminum foil, copper foil, or aluminum alloy tubular foil. The thickness direction of the current collector is the same as the thickness direction of the current collector itself. A coating is provided on part or all of the surface of either side of the current collector; or a coating is provided on part or all of the surface of both sides of the current collector. It is understood that the shape of the coating on the surface of the current collector can be rectangular, elliptical, or any other arbitrary shape, and no specific limitation is made here.

[0020] Generally, silicon-based materials have high energy density, which can improve the energy density of batteries. However, silicon-based materials are prone to significant volume expansion during cycling, especially in solid-state batteries. Excessive expansion of the negative electrode can lead to poor contact between the negative electrode and the solid electrolyte layer, resulting in rapid capacity decay, low ionic conductivity of the negative electrode, poor ion transport performance, and reduced fast-charging performance. Researchers in this invention discovered that adding carbon nanotubes to silicon-based materials can effectively improve the strength of the negative electrode, reduce its expansion rate, and enhance its electronic conductivity. However, while carbon nanotubes themselves have good conductivity and can improve the electronic conductivity of the negative electrode, they cannot effectively improve its ionic conductivity. Furthermore, the inter-particle voids in silicon-based materials result in poor contact between silicon particles, leading to increased battery polarization and decreased energy density. Therefore, a certain amount of sulfide electrolyte material can be added to silicon-based materials to improve the ionic conductivity of the negative electrode, thereby improving the battery's cycle performance and fast charging performance.

[0021] The researchers of this invention also discovered that, compared to other electrolyte materials, the Li7P2S8I electrolyte, a sulfide electrolyte material, has a lower Young's modulus (approximately 10 GPa to 15 GPa, lower than other electrolyte materials, such as other sulfide electrolytes with a Young's modulus of 20 GPa to 25 GPa), resulting in better contact properties and further mitigating the interfacial contact problems caused by silicon-based expansion. Furthermore, when the Li7P2S8I electrolyte is incorporated into silicon-based materials to form the negative electrode, a small amount of LiI is generated during formation, acting as an SEI film. This prevents side reactions between the sulfide electrolyte and silicon-carbon materials, giving the solid-state battery excellent cycle and fast-charging performance.

[0022] Furthermore, by adding carbon nanotubes (with a non-zero mass content) and sulfide electrolyte materials (with a non-zero mass content) to silicon-based materials, the ionic and electronic conductivity of the negative electrode can be improved, effectively mitigating the volume expansion of the negative electrode during cycling and enhancing the battery's cycle performance and fast-charging performance. It is understood that the mass content of the aforementioned sulfide electrolyte material can be controlled by controlling the mass content of iodine in the negative electrode coating. The mass content of iodine in the negative electrode, i.e., the mass content of Li7P2S8I electrolyte, and the mass content of carbon nanotubes, can be measured using inductively coupled plasma atomic emission spectrometry (ICP-AES), atomic absorption spectrometry (AAS), or energy dispersive X-ray spectroscopy (EDS). The expansion rate of the negative electrode can be measured using in-situ thickness measurement, scanning electron microscopy (SEM) observation of the cross-sectional structure, or an expansion force tester; the testing methods for the above parameters are not limited to the examples provided.

[0023] In some embodiments, the mass content of iodine in the coating is set as x, dimensionless; the mass content of carbon nanotubes in the coating is set as y, dimensionless.

[0024] Where x and y are both greater than 0, and x / y satisfies: 1≤x / y≤150.

[0025] As an example, the ratio of the mass content of iodine to the mass content of carbon nanotubes in the coating, i.e., x / y, can only be any one of 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 50, 80, 100, 120, 130, 140, 145, 148, or 150, or any point value between any two. By limiting the mass content ratio of iodine to carbon nanotubes in the negative electrode coating, the mass content of Li7P2S8I electrolyte and carbon nanotubes in the coating can be well controlled. This ensures that the negative electrode has both good ionic and electronic conductivity, while also ensuring good contact between silicon-based material particles in the negative electrode, effectively reducing the battery's internal resistance and improving the battery's fast-charging performance. If the content is outside the above range, it indicates that the mass content of Li7P2S8I electrolyte is too high and the mass content of carbon nanotubes is too low. This may lead to poor contact between silicon-based material particles, decreased electronic conductivity, increased internal resistance of the battery, decreased fast charging performance, and increased risk of lithium plating short circuit. Alternatively, if the mass content of Li7P2S8I electrolyte is too low and the mass content of carbon nanotubes is too high, the ionic conductivity of the negative electrode sheet will be poor, the ion transport efficiency will be reduced, and the electronic conductivity will be increased. This imbalance may cause lithium ions to preferentially gain electrons and reduce to form dendrites instead of diffusing into the electrode, which may lead to lithium plating short circuit at the interface between the negative electrode sheet and the solid electrolyte layer. Furthermore, because the mass content of Li7P2S8I electrolyte is too low, it cannot occupy the gaps well to alleviate the volume expansion of silicon-based material particles, and thus cannot effectively reduce the expansion rate of the negative electrode sheet.

[0026] In some embodiments, the iodine content in the coating is 1wt% to 15wt%.

[0027] For example, the iodine content in the negative electrode can be any one of 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.5wt%, 2wt%, 3wt%, 5wt%, 8wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, or 15wt%, or any value between any two. By limiting the iodine content, the sulfide electrolyte material content in the negative electrode can be well controlled, thus ensuring a good expansion rate for the negative electrode. Simultaneously, the Li7P2S8I electrolyte can effectively prevent contact failure of silicon-based materials, improving the battery's fast-charging performance. If the content is less than the above range, the negative electrode has low ionic conductivity, poor ion transport, and is prone to lithium plating and short circuits, and cannot effectively alleviate the volume expansion of the negative electrode. If the content is greater than the above range, it will cause poor contact between silicon particles, poor electronic conductivity of the negative electrode, increased battery polarization, increased cost, and decreased battery energy density. It is understandable that, as mentioned above, a small amount of LiI will be generated during the formation of Li7P2S8I electrolyte. Therefore, the content of Li7P2S8I electrolyte can be controlled by the mass content of iodine in the negative electrode.

[0028] In some embodiments, the median particle size D of the sulfide electrolyte material v50 Its wavelength ranges from 500 nm to 15 μm.

[0029] For example, the median particle size D of the sulfide electrolyte material v50 The median particle size can be any value between any two of the following: 500nm, 600nm, 700nm, 800nm, 900nm, 950nm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 12μm, 14μm, 14.5μm, or 15μm. Limiting the median particle size range of the sulfide electrolyte material ensures the formation of an ion-electron conductive network on the surface of the silicon-based material particles, thereby improving the battery's fast-charging performance. If the particle size is smaller than the above range, the sulfide electrolyte material will be difficult to disperse during the preparation process. If the particle size is larger than the above range, the sulfide electrolyte material particles will not be able to effectively coat and fill the gaps between the silicon-based material particles, making it difficult to form a complete negative electrode ion-electron conductive network. This will cause the negative electrode to easily plaque lithium and short-circuit, reducing the battery's fast-charging performance. Similarly, the median particle size of sulfide electrolyte materials can also be tested using laser particle size analysis, or by using SEM (scanning electron microscope) or TEM (transmission electron microscope) to scan the sample surface with a high-energy electron beam to obtain the morphology and size information of the particles. Combined with image analysis software, the particle size and distribution can be statistically analyzed.

[0030] In some embodiments, the carbon nanotube content in the coating is 0.1wt% to 1wt%.

[0031] For example, the mass content of carbon nanotubes in the coating can be any one of 0.1wt%, 0.11wt%, 0.12wt%, 0.13wt%, 0.14wt%, 0.15wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 0.95wt%, or 1wt%, or any point between any two. By limiting the mass content range of carbon nanotubes, the electronic conductivity of the negative electrode can be improved, while the volume expansion effect of the negative electrode can be mitigated, thereby improving its fast charging performance. If the carbon nanotube content is outside the aforementioned range, it will cause an imbalance in the ionic and electronic conductivity of the negative electrode. Specifically, too much carbon nanotube will enhance electrolyte side reactions between the negative electrode and the solid electrolyte layer, increase interfacial impedance, make it difficult to disperse during the slurry mixing process, and cause uneven electron transport due to carbon nanotube aggregation, increasing the risk of lithium plating and short circuits in the electrode. Too little carbon nanotube will not effectively alleviate the volume expansion of silicon particles, and will also reduce the electronic conductivity of the negative electrode, hindering electron transport and reducing the fast-charging performance of the negative electrode. The carbon nanotube content can be measured by scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS), or by X-ray fluorescence spectroscopy, elemental analysis, and stoichiometric methods.

[0032] In some embodiments, the diameter ratio of the carbon nanotubes is 8 × 10⁻⁶. 3 ~3.5×10 4 .

[0033] As an example, the value of b can be 8 × 10. 3 8.1×10 3 8.2×10 3 8.5×10 3 9×10 3 1×10 4 1.1×10 4 1.5×10 4 1.8×10 4 2×10 4 2.3×10 4 2.5×10 4 2.8×10 4 3×10 4 3.1×10 4 3.2×10 4 3.3×10 4 3.4×10 4 Or 3.5×10 4The value can be any one of the values ​​or any point between any two of the values. To improve the electronic conductivity of the negative electrode, the diameter ratio of the carbon nanotubes is limited to the above range. This ensures that adding carbon nanotubes to the negative electrode can effectively improve its electronic conductivity, while also increasing its strength and reducing its volume expansion during cycling, i.e., reducing its expansion rate. If the carbon nanotube diameter is smaller than the above range, the improvement in electronic conductivity is less significant, and carbon nanotubes smaller than the range have poor mechanical properties, failing to effectively improve the strength of the negative electrode and thus making it difficult to effectively improve its expansion. If the diameter is larger than the above range, the carbon nanotubes are difficult to disperse. During the preparation process, the carbon nanotubes cannot be well dispersed, easily resulting in uneven dispersion of carbon nanotubes in the active coating on the prepared negative electrode. This leads to inconsistent volume expansion of the active coating, and unevenness on the surface of the active coating away from the current collector, affecting the overall performance of the negative electrode. It is understandable that the tube diameter ratio of carbon nanotubes is the ratio of the length of the carbon nanotube to its diameter; the tube diameter ratio of carbon nanotubes can be tested using SEM or TEM; the expansion rate of the negative electrode sheet can be measured using in-situ thickness measurement, scanning electron microscopy (SEM) to observe the cross-sectional structure, or an expansion force tester.

[0034] Preferably, the length of the carbon nanotubes is 10 μm to 60 μm. Exemplarily, the length of the carbon nanotubes can be any one of 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 18 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 41 μm, 42 μm, 43 μm, 44 μm, 45 μm, 46 μm, 48 μm, 50 μm, 55 μm, or 60 μm, or any value between any two of these.

[0035] Preferably, the diameter of the carbon nanotubes is 1 nm to 3 nm. For example, the diameter of the carbon nanotubes can be any one of 1 nm, 1.1 nm, 1.2 nm, 1.3 nm, 1.4 nm, 1.5 nm, 1.8 nm, 2 nm, 2.2 nm, 2.4 nm, 2.6 nm, 2.8 nm, or 3 nm, or any value between any two of these.

[0036] In some embodiments, the median particle size D of the silicon-based material v50 The range is from 1μm to 15μm.

[0037] For example, the median particle size D of silicon-based materials v50The particle size can be any value between any one or any two of the following: 1μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 12μm, 14μm, 14.5μm, or 15μm. Limiting the median particle size range of silicon-based materials ensures good contact between silicon-based material particles, sulfide electrolyte material particles, and carbon nanotubes, minimizing the likelihood of side reactions. The silicon-based material exhibits good electron and ion transport speeds. However, if the particle size is smaller than the specified range, the silicon-based material will have an excessively large particle size and specific surface area. When silicon-based materials come into contact with sulfide electrolyte materials or carbon nanotubes, numerous side reactions are likely to occur, leading to increased interfacial impedance. Furthermore, in the manufacturing process, silicon-based particles are difficult to disperse and tend to aggregate, causing uneven ion transport and potentially resulting in lithium plating and short circuits on the negative electrode. If the particle size is larger than the specified range, the contact between silicon-based material particles deteriorates, and they are more prone to volume expansion and breakage, affecting ion transport speeds. The median particle size of silicon-based materials can be measured using laser particle size analysis, or by using SEM (scanning electron microscopy) or TEM (transmission electron microscopy) to scan the sample surface with a high-energy electron beam to obtain particle morphology and size information. Combined with image analysis software, the particle size and distribution can be statistically analyzed.

[0038] In some embodiments, the expansion rate of the negative electrode is 50% to 150%.

[0039] As an example, the expansion rate (c) of the negative electrode can be any one of 50%, 51%, 52%, 53%, 54%, 55%, 58%, 60%, 62%, 65%, 70%, 75%, 80%, 90%, 100%, 110%, 115%, 120%, 125%, 130%, 135%, 140%, or 150%, or any value between any two. By limiting the expansion rate of the negative electrode, it can possess excellent ionic conductivity and strength, resulting in good interfacial contact between the negative electrode and the solid electrolyte layer, as well as between the silicon-based material particles, reducing interfacial impedance and improving the cycle performance and energy density of the solid-state battery. If the expansion rate of the negative electrode is less than the above range, the strength of the negative electrode will be too high, leading to poor interfacial contact between the negative electrode and the solid electrolyte layer, resulting in increased interfacial impedance and polarization, severely affecting the cycle performance and energy density of the battery. If the expansion rate of the negative electrode sheet exceeds the above range, it will cause the negative electrode sheet to pulverize and the silicon particles to be crushed, which will reduce the battery's safety performance and ionic conductivity.

[0040] In some embodiments, the surface resistivity of the coating is 5mΩ to 69mΩ.

[0041] For example, the sheet resistance of the coating can be any value or any point between any two of the following: 5mΩ, 6mΩ, 7mΩ, 8mΩ, 9mΩ, 10mΩ, 20mΩ, 25mΩ, 30mΩ, 35mΩ, 40mΩ, 45mΩ, 50mΩ, 55mΩ, 60mΩ, 62mΩ, 64mΩ, 65mΩ, 66mΩ, 67mΩ, 68mΩ, or 69mΩ. By limiting the range of the sheet resistance of the coating, the negative electrode can be well guaranteed to have good ionic and electronic conductivity, resulting in a high energy density for the battery. If the sheet resistance of the coating is too low, the electronic conductivity of the negative electrode will be too strong, while the ionic conductivity will be weak, increasing the risk of lithium plating and short circuits in the negative electrode. If it is too high, the overall impedance of the battery will be too high, resulting in large battery polarization and energy loss. The sheet resistance of the coating can be measured using the four-probe method, the parallel electrode method, or the dual-electrode method.

[0042] In some embodiments, the ionic conductivity of the negative electrode is 0.001 mS / cm to 1 mS / cm.

[0043] As an example, the ionic conductivity of the negative electrode can be any value or any point in between of 0.001 mS / cm, 0.01 mS / cm, 0.1 mS / cm, 0.2 mS / cm, 0.3 mS / cm, 0.4 mS / cm, 0.5 mS / cm, 0.8 mS / cm, 0.9 mS / cm, or 1 mS / cm. By limiting the ionic conductivity of the negative electrode as described above, it is possible to ensure that the negative electrode has a high capacity and good fast-charging performance, without causing an imbalance in the performance of the negative electrode, i.e., one performance is excellent while another performance is poor. It is understood that the ionic conductivity of the negative electrode can be measured by methods such as electrochemical impedance spectroscopy (EIS), Warburg impedance analysis, constant current intermittent titration, and micro-area scanning probe techniques (such as SECM, scanning electrochemical microscopy).

[0044] In some embodiments, the coating thickness is 30 μm to 200 μm.

[0045] For example, the coating thickness refers to the thickness of the coating applied to any side of the current collector's surface along its thickness direction. Specifically, it can be any value between any two of the following: 30μm, 31μm, 32μm, 33μm, 34μm, 35μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, 160μm, 180μm, 190μm, 195μm, or 200μm. By limiting the coating thickness, the negative electrode sheet can be guaranteed to have good mechanical stability, low ion / electron transport resistance, and good charge / discharge rate performance. If the thickness is less than the above range, the energy density will decrease, and pinholes or band breaks will easily occur, affecting the overall performance of the negative electrode sheet. If the thickness exceeds the above range, the ion / electron transport resistance of the negative electrode increases, affecting its fast-charging performance and potentially leading to poor mechanical stability and reduced rate performance of the battery. The thickness of the active coating in the negative electrode can be measured using a contact thickness gauge (micrometer / film thickness gauge) or SEM cross-sectional observation.

[0046] [Preparation method of negative electrode sheet for solid-state batteries] In some embodiments of the present invention, a method for preparing a negative electrode sheet for a solid-state battery is provided, comprising the following steps: S1. Add silicon-based materials, sulfide electrolyte materials, carbon nanotubes and binders to a solvent, stir and ball mill to obtain a slurry.

[0047] The aforementioned silicon-based material, sulfide electrolyte material, carbon nanotubes, and binder are added to a solvent for mixing. The mixing method can be mechanical stirring or magnetic stirring. The main purpose is to disperse the silicon-based material, sulfide electrolyte material, and carbon nanotubes evenly, while allowing the binder to dissolve well and form a binder solution. Further ball milling can better combine the silicon-based material, sulfide electrolyte material, and carbon nanotubes, while also giving the silicon-based material a suitable particle size.

[0048] S2. The slurry is coated onto at least one side of the current collector in the thickness direction and dried to obtain a negative electrode sheet; wherein the sulfide electrolyte material includes Li7P2S8I electrolyte.

[0049] The obtained slurry is coated onto the current collector and dried. Drying methods can include heating and freezing. After drying, a negative electrode sheet is obtained. It is understood that the negative electrode sheet prepared in this embodiment possesses all the properties, effects, and functions of the negative electrode sheets in any of the above embodiments, and will not be repeated here.

[0050] In some embodiments, the silicon-based material includes one or any proportion (mass ratio or molar ratio) of elemental silicon, silicon alloys, and silicon-carbon materials.

[0051] In some embodiments, the adhesive includes one or any proportion (by mass or molar ratio) of polyvinylidene fluoride, polyacrylic acid, styrene-butadiene rubber, chlorinated nitrile rubber, and polyisobutylene. In some embodiments, the solvent includes one or more of N-methylpyrrolidone, deionized water, xylene, and n-heptane in any proportion (by mass or by volume).

[0052] In some embodiments, the solid content of the slurry is 35% to 60%.

[0053] For example, the solid content of the slurry can be any one of 35%, 40%, 42%, 45%, 46%, 47%, 48%, 49%, 50%, 55%, 58%, 59%, or 60%, or any value between any two. When the solid content of the prepared slurry is within the above range, the silicon-based material and carbon nanotubes can be uniformly dispersed in the solvent. Furthermore, it ensures that the slurry is easily coated onto the current collector and does not easily flow on the current collector, thus forming a uniform active coating. If the solid content is too high, the silicon-based material and / or carbon nanotubes will be unevenly dispersed, affecting the overall performance of the negative electrode. If the solid content is too low, the slurry will easily flow after being coated onto the current collector, thus affecting the uniformity of the active coating.

[0054] In some embodiments, the mass ratio of silicon-based material, sulfide electrolyte material, carbon nanotubes, and binder is (15~30):(1.5~15):(0.03~0.4):1. Exemplarily, the mass ratio of silicon-based material, sulfide electrolyte material, carbon nanotubes, and binder can be any one of 15:1.5:0.03:1, 20:5:0.1:1, 25:10:0.3:1, or 30:15:0.4:1, or any ratio between any two of these. By controlling the mass ratio range of silicon-based material, carbon nanotubes, and binder, the resulting negative electrode sheet can have good conductivity and fast charging performance; simultaneously, the negative electrode sheet has a low expansion rate.

[0055] In some embodiments, the ball milling rate is 200 rpm / min to 2000 rpm / min. Exemplarily, the ball milling rate can be any one of 200 rpm / min, 500 rpm / min, 1000 rpm / min, or 2000 rpm / min, or any value between any two. Limiting the ball milling rate can effectively ensure the uniform dispersion of silicon-based materials and carbon nanotubes, and ensure that the silicon-based materials have a suitable particle size, thus ensuring that the obtained negative electrode sheet has excellent overall performance.

[0056] In some embodiments, the drying temperature is 80°C to 120°C, and the drying time is 10 min to 2 h. Exemplarily, the drying temperature can be any value among 80°C, 100°C, or 120°C, and the drying time can be any value among 10 min, 30 min, 1 h, or 2 h.

[0057] [Battery] In some embodiments of the present invention, a battery is provided, comprising: a positive electrode, a solid electrolyte layer, and a negative electrode for a solid-state battery as described in any of the above embodiments.

[0058] In some embodiments, the battery includes a negative electrode sheet prepared by the method for preparing a negative electrode sheet for a solid-state battery in any of the above embodiments.

[0059] Optionally, the positive electrode includes a positive electrode material, which includes, but is not limited to, one or more of lithium iron phosphate, lithium manganese iron phosphate, ternary materials (NCM), LiCoO2, LiNiO2, and LiMn2O4. The solid electrolyte includes, but is not limited to, LGPS electrolyte, Li3PS4 electrolyte, Li3PSe4 electrolyte, and PEO-LiTFSI (lithium polyoxyethylene-bis(trifluoromethanesulfonyl)imide). The positive electrode, solid electrolyte layer, and negative electrode are stacked sequentially to form a cell unit, and the battery includes multiple cell units.

[0060] Optionally, the battery may include an outer packaging that can be used to encapsulate the aforementioned electrode components and electrolyte. The outer packaging of the battery may be a rigid shell, such as a hard plastic shell, aluminum shell, steel shell, etc. Specifically, the rigid shell may include a housing and a cover plate, wherein the housing may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates enclosing a receiving cavity, the housing having an opening communicating with the receiving cavity, and the cover plate being able to cover the opening to close the receiving cavity, and the battery cell unit being encapsulated within the receiving cavity.

[0061] The solid electrolyte layer in this embodiment is a solid electrolyte used in the art, and is not particularly limited here.

[0062] Since the battery provided in this embodiment of the invention adopts all the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, and will not be described in detail here.

[0063] The following examples illustrate this application in detail, but the implementation and protection of this invention are not limited thereto. The following embodiments are only some embodiments of this application and are not intended to limit this application.

[0064] Silicon-based materials: specifically elemental silicon, with a median particle size D. v50 The range is from 1μm to 15μm.

[0065] Carbon nanotubes: Specifically, single-walled carbon nanotubes, with lengths ranging from 10 μm to 60 μm, diameters from 1 nm to 3 nm, and a tube-to-diameter ratio of 8 × 10⁻⁶. 3 ~3.5×10 4 Available for sale in the market.

[0066] Li7P2S8I electrolyte: specifically Li7P2S8I, median particle size D v50 It has a wavelength of 500nm to 15μm and is commercially available.

[0067] Example 1 (1) Preparation of negative electrode sheet: S11. Silicon-based material, carbon nanotubes, Li7P2S8I electrolyte and binder polyvinylidene fluoride in a mass ratio of 18:1.6:0.03:1 are added to the solvent N-methylpyrrolidone and ultrasonically dispersed for 20 min. After preliminary mixing, the mixture is transferred to a ball mill jar, the ball mill speed is adjusted to 800 rpm / min, and the mixture is ball milled for 20 min. After that, it is vacuum dried in a vacuum oven at 100℃ for 12 h to obtain the negative electrode material.

[0068] S12. Add the negative electrode material to the solvent N-methylpyrrolidone and stir for 2 hours to disperse completely to obtain a slurry; the solid content of the slurry is 45%; coat the slurry evenly on both sides of the copper foil, dry it at 120℃ for 10 minutes, and then compact it with a roller press to obtain the negative electrode sheet.

[0069] (2) Preparation of positive electrode sheet: Weigh a certain amount of positive electrode material NCM811, conductive agent VGCF (vapor-grown carbon fiber), and electrolyte Li6PS5Cl (80wt%: 1wt%: 16wt%). Pour the above materials into a pulverizer and mix them evenly. Continue to add 3%wt of PTFE (polytetrafluoroethylene) binder powder and mix evenly. Preheat and stir at 80℃ until the binder PTFE is fiberized. Place the above mixed material in a roller press and roll it into a dry film with a thickness of 160μm and attach a current collector to obtain the positive electrode sheet.

[0070] (3) Preparation of solid electrolyte layer: Add electrolyte Li6PS5Cl (97%wt) and binder nitrile rubber (3wt%) to the slurry mixing tank, and continue to add solvent xylene to adjust the solid content of the slurry to 45% to obtain electrolyte slurry. Coat the negative electrode sheet and dry it at 120℃ for 15min to obtain negative electrode-electrolyte composite electrode sheet.

[0071] (4) Battery assembly: Cut the positive electrode sheet and the composite negative electrode sheet into the required size and weld the tabs. Then, hot press the positive electrode sheet at 70°C onto the electrolyte layer side of the above-mentioned negative electrode-electrolyte composite electrode sheet to obtain the battery cell. Subsequently, the battery cell is packaged and isostatically pressed to obtain a solid-state battery.

[0072] In addition to the differences between Examples 2 to 6, Comparative Examples 1 to 2 and Example 1, as shown in Table 1, the following limited differences also exist: Example 2 The preparation was carried out according to the method of Example 1, except that D was used. v50 The D in Example 1 was replaced with a Li7P2S8I electrolyte with a wavelength of 500 nm. v50 =1μm Li7P2S8I electrolyte; and the mass ratio of silicon-based material, carbon nanotubes, Li7P2S8I electrolyte and binder polyvinylidene fluoride is adjusted to 15:14:0.03:1.

[0073] Example 3 The preparation was carried out according to the method of Example 1, except that a tube with a length of 16 μm, a diameter of 2 nm, and a diameter-to-diameter ratio of 8 × 10⁻⁶ was used. 3 The carbon nanotubes used in Example 1 have a length of 30 μm, a diameter of 2 nm, and a diameter-to-diameter ratio of 1.5 × 10⁻⁶. 4 The carbon nanotubes; and the mass ratio of silicon-based material, carbon nanotubes, Li7P2S8I electrolyte and binder polyvinylidene fluoride is adjusted to 22:13.5:0.19:1.

[0074] Example 4 The preparation was carried out according to the method of Example 1, except that D was used. v50 A silicon-based material with a diameter of 15 μm replaced D in Example 1. v50 =6μm silicon-based material; and the mass ratio of silicon-based material, carbon nanotubes, Li7P2S8I electrolyte and binder polyvinylidene fluoride is adjusted to 30:13:0.4:1.

[0075] Example 5 The preparation was carried out according to the method of Example 1, except that D was used. v50 The D in Example 1 was replaced with a Li7P2S8I electrolyte with a particle size of 15 μm. v50 =1μm Li7P2S8I electrolyte; and the mass ratio of silicon-based material, carbon nanotubes, Li7P2S8I electrolyte and binder polyvinylidene fluoride is adjusted to 26:11:0.32:1.

[0076] Example 6 The preparation was carried out according to the method of Example 1, except that a coating with an iodine content of 12 wt% was used instead of the coating with an iodine content of 1 wt% in Example 1; and the mass ratio of silicon-based material, carbon nanotubes, Li7P2S8I electrolyte and binder polyvinylidene fluoride was adjusted to 20:8:0.3:1.

[0077] Comparative Example 1 The preparation was carried out according to the method of Example 1, except that a coating with an iodine content of 15 wt% was used instead of the coating with an iodine content of 1 wt% in Example 1.

[0078] Comparative Example 2 The tube was prepared according to the method in Example 1, except that it had a length of 35 μm, a diameter of 1 nm, and a diameter-to-diameter ratio of 3.5 × 10⁻⁶. 4 The carbon nanotubes used in Example 1 have a length of 30 μm, a diameter of 2 nm, and a diameter-to-diameter ratio of 1.5 × 10⁻⁶. 4 Carbon nanotubes.

[0079] Performance testing: 1. Mass content of silicon in the negative electrode (ICP-MS method): 1.1 Electrode pretreatment is completed in a glove box, with no water or oxygen throughout the process. The active material of the electrode is scraped off, and the copper or aluminum foil current collector is removed to avoid interference from the metal matrix. Then, it is ground into a fine powder of 200 mesh in an agate mortar and mixed evenly. 0.05~0.2g of sample is weighed and placed in a polytetrafluoroethylene inner container for microwave digestion.

[0080] The closed microwave digestion process involves first adding 5 mL of ultrapure water and 8 mL of 25% TMAH (tetramethylammonium hydroxide) to the container, gently shaking to moisten the sample; then adding 1-2 mL of 30% H2O2, sealing the digestion container, placing it in a microwave oven, and setting the microwave temperature program: increasing the temperature from room temperature to 120°C within 5 minutes and holding for 10 minutes; then increasing the temperature from 120°C to 180°C within 8 minutes and holding for 20 minutes; finally, allowing it to cool naturally to room temperature.

[0081] After volume adjustment and pretreatment cooling, transfer the digestion solution to a 50mL volumetric flask; rinse the digestion vessel multiple times with ultrapure water, and add all the washings to the volumetric flask; bring the volume to the mark, shake well, and filter through a 0.22μm filter membrane to remove toner and binder residue.

[0082] 1.2 Standard Curve and ICP-MS Parameters: Preparation of standard solutions: Prepare iodine gradient standard solutions with LiI at concentrations of 0 μg / L, 0.1 μg / L, 1 μg / L, 5 μg / L, 10 μg / L and 50 μg / L, and then add TMAH matrix of equal concentration to each solution.

[0083] ICP-MS acquisition: m / z=127 ( 127 I), Internal standard selection 115 In corrects matrix drift.

[0084] Collision mode: Activate the helium collision cell to eliminate S and P matrix mass spectrometry interference.

[0085] 1.3 Calculation formula: w(I, %) = (C × V × F) / (m × 10 6 ) ×100; The iodine concentration was measured on the instrument, and the unit is μg / mL.

[0086] Where V is the total volume of digestion and final volume adjustment (mL); F – Dilution factor; m — mass of the sample — g.

[0087] 2. Mass content of iodine in the negative electrode (thermogravimetric method): Pretreatment: Scrape off the complete active powder from the silicon carbide electrode and remove copper foil and membrane impurities; dry the powder in an 80℃ forced-air oven for 2 hours, cool to room temperature and store in a desiccator; preheat the empty alumina crucible to 850℃ for 30 minutes, cool to constant weight, and record the mass of the empty crucible as m0.

[0088] Weigh 10 mg of the powder to be tested into a constant weight crucible; place it into the TGA furnace, seal it, purge the furnace with air for 10 minutes to remove the inert gas, call the set heating program, and start the test.

[0089] Read the key mass points of TGA, export the curve after the test ends, and take 3 characteristic masses: m1: the mass after the isothermal end at 100℃, that is, the mass after the moisture and residual solvent are completely removed; m2: the mass at the plateau at 600℃, that is, the mass after all carbon, binder and conductive agent are burned off, leaving only unoxidized silicon; m3: the mass at the isothermal endpoint at 850℃, that is, the mass after Si is completely oxidized to SiO2.

[0090] Calculate: The mass of SiO2 generated Δm = m3 - m2 —— (1) Mass of elemental Si in the sample: mSi = Δm × Msi / MSiO2 — (2) Silicon mass fraction: w(Si,%) = mSi / m1 × 100% — (3).

[0091] 3. Carbon nanotube diameter ratio: The diameter and length of carbon nanotubes were observed and measured using transmission electron microscopy (TEM). CNTs were dispersed in ethanol and acetone, sonicated, and then dropped onto a microgrid copper grid and dried. The diameter was measured directly under the electron microscope using a scale, and the average value was taken for 50 or more nanotubes.

[0092] 4. Median particle size of silicon-based material in negative electrode: Particle size was tested using a particle size analyzer. 0.3g of silicon carbide powder was placed in a 50mL beaker, 20mL of anhydrous ethanol was added as a dispersion medium, and the mixture was ultrasonically dispersed for 3-5 minutes before testing. The test values ​​were recorded.

[0093] 5. Median particle size of Li7P2S8I electrolyte in negative electrode sheet: Particle size was tested using a dry method with a particle size analyzer. 0.3g of powder was placed in the material hopper of the analyzer, the air pump was turned on, and the test was performed according to the program. The test values ​​were recorded.

[0094] 6. Expansion rate of negative electrode: Test the stacking pressure of the assembled battery at 100 MPa and temperature at 45°C, and let it stand for 4-8 hours to confirm that the voltage is normal. During the test, first discharge at 0.05C to -0.595V, let it stand for 5 minutes, and then charge at 0.05C to 0.9V. Target SOC control: Stop lithium intercalation at a specific capacity point of 100% SOC as needed.

[0095] The assembled molded battery was placed in a constant temperature test chamber and connected to an in-situ expansion tester sensor. The expansion rate data of the battery under different SOCs was recorded in situ.

[0096] 7. Surface resistance of the coating in the negative electrode: A four-probe resistance meter was used.

[0097] Cut the electrode sheet into 5×10cm or 4×8cm pieces, ensuring the surface is free of oil and warping, and allow it to stand to equilibrate for temperature and humidity. Then, preheat the instrument for 15-20 minutes, calibrating it using a standard resistance block and thickness block to confirm the probe is clean and free of wear. Lay the electrode sheet flat on the sample stage, designating the central area as the test zone, avoiding the edges and coating boundaries as much as possible. Apply gentle, vertical pressure with the probe, controlling the pressure to the set value.

[0098] Select a negative electrode corresponding to a pressure of 25 MPa and a holding time of 10 seconds, enable thickness synchronous acquisition, and set the current range. After the holding time is complete, start the test and record the resistance, thickness, and resistivity; perform multi-point testing on the same sample, switching voltage terminals to measure sides A and B.

[0099] Data processing: Remove outliers, calculate the mean and standard deviation; convert surface resistance (Ω / cm) according to the formula, and record environmental conditions.

[0100] 8. Test method for carbon nanotube content: Cut 5-10 mg of sample from the negative electrode sheet and heat it to 800 °C at 10 °C / min in air. Record the thermogravimetric curves from 30 to 800 °C. The mass fraction of carbon nanotubes is calculated by subtracting the blank control of pure conductive agent and binder system from the mass fraction of mass loss corresponding to the range of 450-600 °C, based on the standard CNT oxidation kinetic curve.

[0101] 9. Thickness of the coating in the negative electrode sheet: Measure manually with a thickness gauge, and take the average value after three measurements.

[0102] 10. Ionic conductivity: Assemble a symmetrical battery consisting of Li, SE (electrolyte), composite negative electrode, SE and Li. Through the polarization potential test step, set the applied voltage to 0.03V, the test time to 3600s, take the steady-state current Iss, calculate the battery ion conduction resistance using the formula R=U / Iss, and calculate the electrode ion conductivity using the formula σ=L / R×S.

[0103] 11. Fast charging capacity retention rate: After battery activation, the battery is charged at a constant current of 0.1C until the cutoff voltage is reached. Then, the charging is switched to constant voltage charging at the cutoff voltage until the charging current drops to 0.02C. The capacity C0 is recorded. The battery is then charged at a constant current of 1C with a preset fast charging current until the battery reaches the full charge cutoff voltage of 4.2V. After the cutoff voltage is reached, the charging is switched to constant voltage charging at the cutoff voltage until the charging current drops to 0.02C. Charging is then stopped, and the battery is discharged at a constant current of 0.1C until the cutoff voltage is reached. The capacity C1 is recorded. Fast charging performance is evaluated using the fast charging capacity retention rate.

[0104] Capacity retention rate = (C1 / C0) × 100%, and the average value is taken from three measurements.

[0105] The above tests are shown in Table 1.

[0106] Table 1 As can be seen from the results in Table 1, compared with Comparative Examples 1 and 2 which only added Li7P2S8I electrolyte or carbon nanotubes, the negative electrode in the examples has good ionic conductivity and electronic conductivity. The volume expansion of the negative electrode during cycling is low, and the battery obtained by the negative electrode has a better fast charging capacity retention rate at 1C than the battery obtained by the negative electrode in the comparative examples.

[0107] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0108] In the above embodiments, the descriptions of each embodiment have their own emphasis. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments. The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification.

[0109] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the following claims.

[0110] It should be noted that the terms "and / or" or " / " used herein are merely descriptions of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The singular forms "a," "described," and "the" used in the embodiments of the invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0111] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0112] It should be understood that the present invention is not limited to the precise structure described above, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A negative electrode sheet for solid-state batteries, characterized in that, include: A current collector, and a coating disposed on at least one surface of the current collector in the thickness direction; The coating comprises silicon-based materials, sulfide electrolyte materials, and carbon nanotubes; The sulfide electrolyte material includes Li7P2S8I electrolyte.

2. The negative electrode sheet for a solid-state battery according to claim 1, characterized in that, The mass content of iodine in the coating is set as x, dimensionless; the mass content of carbon nanotubes in the coating is set as y, dimensionless. Wherein, both x and y are greater than 0, and x / y satisfies: 1≤x / y≤150.

3. The negative electrode sheet for a solid-state battery according to claim 1 or 2, characterized in that, The iodine content in the coating is 1wt% to 15wt%.

4. The negative electrode sheet for a solid-state battery according to claim 3, characterized in that, The median particle size D of the sulfide electrolyte material v50 Its wavelength ranges from 500 nm to 15 μm.

5. The negative electrode sheet for a solid-state battery according to claim 1 or 2, characterized in that, The carbon nanotubes in the coating have a mass content of 0.1wt% to 1wt%.

6. The negative electrode sheet for a solid-state battery according to claim 5, characterized in that, The diameter ratio of the carbon nanotubes is 8×10. 3 ~3.5×10 4 .

7. The negative electrode sheet for a solid-state battery according to claim 6, characterized in that, The length of the carbon nanotubes is 10μm~60μm; And / or, the diameter of the carbon nanotubes is 1 nm to 3 nm.

8. The negative electrode sheet for a solid-state battery according to claim 1, characterized in that, The median particle size D of the silicon-based material v50 The range is from 1μm to 15μm.

9. The negative electrode sheet for a solid-state battery according to claim 1, characterized in that, The expansion rate of the negative electrode sheet is 50%~150%.

10. The negative electrode sheet for a solid-state battery according to claim 1, characterized in that, The surface resistivity of the coating is 5mΩ~69mΩ.

11. The negative electrode sheet for a solid-state battery according to claim 1, characterized in that, The ionic conductivity of the negative electrode is 0.001 mS / cm to 1 mS / cm.

12. The negative electrode sheet for a solid-state battery according to claim 1, characterized in that, The thickness of the coating is 30μm to 200μm.

13. A method for preparing a negative electrode sheet for a solid-state battery, characterized in that, Includes the following steps: Silicon-based materials, sulfide electrolyte materials, carbon nanotubes, and binders are added to a solvent, stirred, and ball-milled to obtain a slurry. The slurry is coated onto at least one side of the current collector surface in the thickness direction and dried to obtain the negative electrode sheet; wherein the sulfide electrolyte material includes Li7P2S8I electrolyte.

14. The method for preparing the negative electrode sheet for a solid-state battery according to claim 13, characterized in that, The silicon-based material includes at least one of elemental silicon, silicon alloys, and silicon-carbon materials; And / or, the adhesive comprises at least one of polyvinylidene fluoride, polyacrylic acid, styrene-butadiene rubber, chlorinated nitrile rubber, and polyisobutylene; And / or, the solvent includes at least one of N-methylpyrrolidone, deionized water, xylene, and n-heptane.

15. The method for preparing the negative electrode sheet for a solid-state battery according to claim 13, characterized in that, The solid content of the slurry is 35%~60%; And / or, the mass ratio of the silicon-based material, sulfide electrolyte material, carbon nanotubes and binder is (15~30):(1.5~15):(0.03~0.4):

1.

16. The method for preparing the negative electrode sheet for a solid-state battery according to claim 13, characterized in that, The ball milling speed is 200 rpm / min to 2000 rpm / min; And / or, the drying temperature is 80℃~120℃, and the drying time is 10min~2h.

17. A battery, characterized in that, include: A positive electrode, a solid electrolyte layer, and a negative electrode for a solid-state battery as described in any one of claims 1 to 12; Alternatively, the negative electrode sheet prepared by the preparation method according to any one of claims 13 to 16.

Images