Negative electrode material and battery

Abstract

The present application relates to the technical field of negative electrode materials. Provided are a negative electrode material and a battery. The negative electrode material comprises an inner core and a coating layer located on at least part of the surface of the inner core. The inner core comprises a carbon matrix, and an active substance and boron element distributed in the carbon matrix. The active substance comprises a silicon material and a metal material, and at least part of the silicon material being connected to the metal material. The negative electrode material of the present application has low expansion, ultra-high conductivity, and high initial coulombic efficiency.

Description

Negative electrode material and battery TECHNICAL FIELD

[0001] The present application relates to the technical field of negative electrode materials, and particularly relates to a negative electrode material and a battery. BACKGROUND

[0002] Lithium ion batteries have advantages of high energy density, long service life and no environmental pollution, and have been widely used in the 3C field. With the development of the market, lithium ion batteries are not only widely used in mobile devices such as smart phones and portable computers, but also applied to large equipment fields such as electric vehicles and electric tools. In order to improve the energy density of the battery, the research and development of silicon-based negative electrode materials are becoming mature. Silicon will undergo a large volume change during lithiation / delithiation, which will cause the material to break, powder, fall off from the current collector and the continuous growth of the solid electrolyte interface, ultimately leading to the capacity decay of the battery.

[0003] To solve these problems, silicon-carbon negative electrode materials have emerged. Although the introduction of porous carbon materials can improve the electrical conductivity of silicon-based negative electrode materials and inhibit expansion, the porous carbon often includes a large amount of amorphous carbon structure, and its ability to improve the electrical conductivity is limited, and the electrical conductivity of the silicon-carbon negative electrode material is often small.

[0004] Therefore, how to make the negative electrode material have both ultrahigh electrical conductivity and high initial coulombic efficiency is still a problem to be solved at present.

[0005] SUMMARY

[0006] The present application provides a negative electrode material and a battery, and the negative electrode material has both ultrahigh electrical conductivity and high initial coulombic efficiency.

[0007] In a first aspect, the present application provides a negative electrode material, which comprises a core and a coating layer located on at least part of the surface of the core, the core comprises a carbon matrix, an active substance and a boron element distributed in the carbon matrix, the active substance comprises a silicon material and a metal material, and at least part of the silicon material and the metal material are connected.

[0008] In some embodiments, the mass percentage content of the metal element in the negative electrode material is A%, the mass percentage content of the silicon element in the negative electrode material is B%, and the negative electrode material satisfies: 0.03

[0009] In some embodiments, 1.4

[0010] In some embodiments, the metal material comprises at least one of lithium particles, magnesium particles and sodium particles.

[0011] In some embodiments, the mass percentage content of boron element in the negative electrode material is C%, 0.4

[0012] In some embodiments, the carbon matrix has pores, and at least part of the boron atoms are distributed on the pore walls of the carbon matrix.

[0013] In some embodiments, the silicon material comprises at least one of silicon element, silicon oxide and silicon alloy.

[0014] In some embodiments, the silicon material comprises silicon oxide, and the general formula of the silicon oxide is SiO x , wherein 0.5≤x<2.

[0015] In some embodiments, the silicon material comprises crystalline silicon and / or amorphous silicon.

[0016] In some embodiments, the average particle size of the silicon material is 1 nm to 50 nm.

[0017] In some embodiments, the carbon matrix comprises at least one of amorphous carbon, graphitized carbon, mesocarbon microbeads and carbon gel.

[0018] In some embodiments, the negative electrode material has pores, and the total pore volume of the negative electrode material is 0.001 cm 3 / g to 0.1 cm 3 / g.

[0019] In some embodiments, the thickness of the coating layer is 5 nm to 20 nm.

[0020] In some embodiments, the coating layer comprises at least one of carbon, nitride, metal oxide, metal fluoride, metal oxyfluoride and polymer.

[0021] In some embodiments, the specific surface area of the negative electrode material is less than 10 m 2 / g.

[0022] In some embodiments, the volume distribution median particle size D50 of the negative electrode material is 5 μm to 10 μm.

[0023] In some embodiments, the powder conductivity of the negative electrode material under a pressure of 20 KN is 8 S / cm to 30 S / cm.

[0024] In some embodiments, the mass percentage content of oxygen element in the negative electrode material is less than 4%.

[0025] In some embodiments, the mass percentage content of carbon element in the negative electrode material is 35% to 55%.

[0026] In a second aspect, the present application provides a battery, which comprises the negative electrode material.

[0027] The technical scheme of the present application has at least the following beneficial effects:

[0028] The negative electrode material provided by the present application has a core-shell structure, the inner core comprises a carbon matrix and active substances and boron elements distributed in the carbon matrix, the boron elements are doped into the carbon matrix, the P empty orbit of the boron atom can form a P-π conjugate system with the π-π conjugate system of the carbon matrix due to the P empty orbit of the boron atom, the electron orbit of the conjugate system is increased, the electron flow in the carbon matrix is enhanced, and thus the conductivity of the negative electrode material is enhanced. In addition, the connection between the metal material and the silicon material can enhance the conductivity of the negative electrode material due to the excellent conductivity of the metal material. The surface of the inner core at least partially has a coating layer, the existence of the coating layer can reduce the specific surface area of the negative electrode material, reduce the side reaction between the active substances and the electrolyte, and improve the initial coulomb efficiency of the negative electrode material. In the present application, the three-dimensional conductive network formed by the coating layer, the boron-doped carbon matrix and the metal material can greatly improve the conductivity of the negative electrode material, and the negative electrode material has high conductivity, high initial coulomb efficiency and excellent fast charging performance. BRIEF DESCRIPTION OF DRAWINGS

[0029] Fig. 1 is a structural schematic diagram of the negative electrode material provided by the present application.

[0030] Fig. 2 is a flow schematic diagram of the preparation method of the negative electrode material provided by the present application.

[0031] Fig. 3 is a schematic diagram of the discharge state of the battery provided by the present application. DETAILED DESCRIPTION

[0032] The present application will be explained by the following examples, which are exemplary and only used to explain the present application, but cannot be explained as a limitation to the present application.

[0033] In a first aspect, the present application provides a negative electrode material, as shown in Fig. 1, which comprises an inner core 10 and a coating layer 20 located on at least a part of the surface of the inner core 10, the inner core 10 comprises a carbon matrix 11, active substances 12 and boron elements 13 distributed in the carbon matrix 11, the active substances 12 comprise silicon materials 14 and metal materials 15, and at least a part of the particles of the silicon materials 14 and the particles of the metal materials 15 are connected.

[0034] In the present application, the particles of the silicon materials 14 and the particles of the metal materials 15 are in contact, and electrons flow between them.

[0035] The negative electrode material provided in the application has a core-shell structure, the inner core comprises a carbon matrix and active substances and boron elements distributed in the carbon matrix, the boron elements are doped into the carbon matrix, the P-empty orbit of the boron atom can form a P-pi conjugated system with the pi-pi conjugated system of the carbon matrix due to the P-empty orbit of the boron atom, the electron orbit of the conjugated system is increased, the electron flow in the carbon matrix is enhanced, and then the conductivity of the negative electrode material is enhanced. In addition, the connection of the metal material and the silicon material can enhance the conductivity of the negative electrode material due to the excellent conductivity of the metal material. The surface of the inner core has a coating layer, the specific surface area of the negative electrode material can be reduced due to the coating layer, the side reaction between the active substances and the electrolyte is reduced, and the first coulomb efficiency of the negative electrode material can be improved. In the application, the three-dimensional conductive network formed by the coating layer, the boron-doped carbon matrix and the metal material can greatly improve the conductivity of the negative electrode material, and the negative electrode material has high electrical conductivity, high first coulomb efficiency and excellent fast charging performance.

[0036] In some embodiments, the mass percentage content of the metal element in the negative electrode material is A%, the mass percentage content of the silicon element in the negative electrode material is B%, and 0.03

[0037] In some embodiments, the mass percentage content of the metal element in the negative electrode material is A%, and 1.4

[0038] In some embodiments, the mass percentage of silicon in the negative electrode material is B%, and 42 < B < 58. Specifically, it can be 43%, 44%, 45%, 48%, 50%, 52%, 51%, 53%, 55%, or 57.9%, without being limited herein. Controlling the mass percentage of silicon in the negative electrode material within the above range is beneficial to the negative electrode material having both high specific capacity and high initial coulombic efficiency.

[0039] In some embodiments, the mass percentage of boron in the negative electrode material is C%, and 0.4 < C < 1.7. Specifically, it can be 0.41%, 0.44%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.6%, 1.65%, or 1.69%, without being limited herein. Since the decomposition of metal borate produces metal and borane, the boiling point of borane is low, and it is easy to volatilize. The doping efficiency of boron is low. Increasing the mass percentage of boron in the negative electrode material will increase the production cost. When the mass percentage of boron in the negative electrode material is too low, it is difficult to effectively improve the electronic conductivity of the carbon matrix by boron. Controlling the mass percentage of boron within the above range is beneficial to increasing the electronic conductivity of the carbon matrix and improving the fast-charging performance of the negative electrode material.

[0040] In some embodiments, the carbon matrix includes at least one of amorphous carbon, graphitized carbon, mesocarbon microbeads, and carbon gel. The carbon matrix can improve the conductivity of the negative electrode material.

[0041] In some embodiments, the carbon matrix has pores, and at least part of the active material is filled in the pores of the carbon matrix. It can be understood that the active material is filled in the pores of the carbon matrix, which ensures the dispersive distribution of the active material and the carbon matrix. On the one hand, it can improve the specific capacity of the negative electrode material. On the other hand, the porosity of the carbon matrix after filling the active material can be reduced, which can improve the density of the negative electrode material, effectively reduce the occurrence of side reactions between the negative electrode material and the electrolyte, and further improve the cycle performance of the material.

[0042] In some embodiments, the metal material includes at least one of lithium particles, magnesium particles, and sodium particles.

[0043] In some embodiments, the metal material includes lithium particles. The appropriate amount of lithium particles distributed in the carbon matrix can realize the pre-lithiation of the negative electrode material. The active lithium ions generated by the lithium particles in the first charge and discharge process can participate in the establishment of the solid electrolyte membrane, thereby improving the initial coulombic efficiency of the negative electrode material.

[0044] In some embodiments, the silicon material can also form a silicon alloy with the metal material, such as a silicon-lithium alloy, a silicon-magnesium alloy, a silicon-sodium alloy, etc. It should be noted that in some cases, the active material includes the silicon material, the metal material, and the alloy thereof.

[0045] In some embodiments, the silicon material includes at least one of elemental silicon, silicon oxide, and silicon alloy.

[0046] In some embodiments, the silicon alloy may be at least one of silicon-lithium alloy, silicon-magnesium alloy, etc., and is not limited thereto.

[0047] In some embodiments, the elemental silicon includes amorphous silicon and / or crystalline silicon; preferably, the elemental silicon includes amorphous silicon, which expands isotropically during lithium intercalation, thereby reducing the collapse of the pore structure, suppressing rapid capacity decay, and improving the lithium intercalation cycle performance of the anode material.

[0048] In some embodiments, the general formula for silicon oxide is SiO. x Where 0.5 ≤ x < 2. Specifically, SiO x Specifically, it could be SiO 0.5 SiO 0.7 SiO 0.9 SiO, SiO 1.2 SiO 1.5 SiO 1.8 SiO 1.9 etc. are not specified here.

[0049] In some embodiments, the silicon material includes silicon particles and a silicon oxide layer on the surface of the silicon particles. The silicon oxide layer includes silicon oxide, the general formula of which is SiO. x Where 0.5 ≤ x < 2. Specifically, SiO x Specifically, it could be SiO 0.5 SiO 0.7 SiO 0.9 SiO, SiO 1.2 SiO 1.5 SiO 1.8 SiO 1.9 etc. are not specified here.

[0050] In some embodiments, the silicon material comprises silicon particles and a silicon oxide layer on the surface of the silicon particles, and the mass percentage of oxygen atoms in the silicon material is 1% to 18%, based on 100% of the mass of the silicon material. Specifically, the mass percentage of oxygen atoms in the silicon material can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17% or 18%, etc., which is not limited herein. Controlling the mass percentage of oxygen atoms in the silicon material within the above range is beneficial to forming a stable silicon oxide layer on the surface of the silicon particles, which can reduce the direct contact between the silicon particles and the electrolyte, thereby reducing the side reaction between the silicon particles and the electrolyte and improving the cycle stability of the negative electrode material. It can also ensure that the silicon material has stable activity and improve the specific capacity of the negative electrode material.

[0051] In some embodiments, the average particle size of the silicon material is 1 nm to 50 nm. Optionally, the average particle size of the silicon material can be specifically 1 nm, 2 nm, 5 nm, 10 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm or 50 nm, etc., or other values within the range, which can be selected according to actual needs, which is not limited herein. The mechanical stress of the expanded silicon material decreases with the decrease of the particle size, and the size can be reduced to shorten the electron and ion transmission path. At the same time, the size of the silicon material is reduced, and the gap between adjacent silicon materials is increased, which can reserve space for the expansion of the silicon material. It can be understood that the average particle size of the silicon material within the above range can ensure the battery capacity of the lithium ion battery and reduce the irreversible capacity loss. Preferably, the average particle size of the silicon material is 1 nm to 10 nm.

[0052] In some embodiments, the morphology of the silicon material includes at least one of a point shape, a spherical shape, an ellipsoidal shape and a sheet shape, which can be selected according to actual needs, which is not limited herein.

[0053] In some embodiments, the thickness of the coating layer is 5 nm to 20 nm, which can be specifically 5 nm, 6 nm, 8 nm, 10 nm, 12 nm, 15 nm, 18 nm or 20 nm, etc., which is not limited herein. In the present application, the thickness of the coating layer is controlled within the above range, which is beneficial to reducing the specific surface area of the negative electrode material, reducing the side reaction activity of the metal material, improving the safety of the negative electrode material, and improving the first coulombic efficiency of the negative electrode material. When the coating layer is too thin, the risk of contact between the metal material and the outside increases, and the metal material is easily oxidized, even self-ignited, and the safety performance of the negative electrode material decreases. When the coating layer is too thick, the active ion transmission efficiency in the electrolyte decreases, the interface impedance between the negative electrode material and the electrolyte increases, and the fast charging performance of the negative electrode material decreases.

[0054] In some embodiments, the coating layer includes at least one of carbon, nitride, metal oxide, metal fluoride, metal oxyfluoride, and polymer.

[0055] In some embodiments, the coating layer can include lithium-ion permeable carbon, which can include at least one of graphene, soft carbon, hard carbon, and the like. The presence of the coating layer can effectively inhibit the volume expansion of the anode material, reduce the structural damage of the anode material during the cycling process, and also enhance the mechanical strength and pressure resistance of the anode material.

[0056] In some embodiments, the coating layer can include lithium-ion permeable nitride, which can include at least one of titanium nitride, vanadium nitride, cobalt nitride, nickel nitride, and carbon nitride.

[0057] In some embodiments, the coating layer can include lithium-ion permeable metal oxide, which can include at least one of titanium oxide, aluminum oxide, lithium oxide, cobalt oxide, and vanadium oxide.

[0058] In some embodiments, the coating layer can include aluminum oxide. In some cases, oxides of other metals that naturally form a protective oxide layer on the surface can be used instead of aluminum oxide. These include, but are not limited to, titanium oxide (Ti), chromium oxide (Cr), tantalum oxide (Ta), niobium oxide (Nb), and the like. A variety of oxide coating deposition techniques can be used to deposit such an oxide coating, including physical vapor deposition, chemical vapor deposition, magnetron sputtering, atomic layer deposition, microwave-assisted deposition, wet chemistry, and the like.

[0059] For example, a metal oxide precursor in the form of a water-soluble salt can be added to a suspension of the core particles (in water). The addition of a base (e.g., sodium hydroxide or an amine) results in the formation of a metal (M) hydroxide. The core particles suspended in the mixture can then act as nucleation sites for the M-hydroxide precipitation. Once the core particles are coated with a shell of M-hydroxide, they can be annealed to convert the hydroxide shell to the corresponding oxide layer, which then adheres well to the surface of the anode material.

[0060] In some embodiments, the coating layer includes lithium-ion permeable metal fluoride or metal oxyfluoride. Examples of such metal fluoride materials include, but are not limited to, vanadium fluoride, vanadium oxyfluoride, iron fluoride, iron oxyfluoride, aluminum fluoride, aluminum oxyfluoride, titanium fluoride, titanium oxyfluoride, aluminum fluoride, aluminum oxyfluoride, zinc fluoride, zinc oxyfluoride, niobium fluoride, niobium oxyfluoride, tantalum fluoride, tantalum oxyfluoride, nickel fluoride, nickel oxyfluoride, magnesium fluoride, magnesium oxyfluoride, copper fluoride, copper oxyfluoride, manganese fluoride, and manganese oxyfluoride.

[0061] In some embodiments, the coating layer includes a lithium-ion permeable polymer.

[0062] In some embodiments, the polymer layer is a conductive polymer. In other embodiments, the polymer is an electrically insulating polymer. Examples of lithium ion permeable polymers include, but are not limited to, sulfonated polystyrene grafted fluorinated ethylene propylene, sulfonated inorganic-organic hybrid polymers, partially fluorinated polystyrene, organically modified layered phosphonates, polyphenylene sulfide, polyether ether, polysaccharide, poly(ethylene) glycol), and polyethylene oxide.

[0063] In some embodiments, the coating layer can have several layers (2 or more) of different lithium ion permeable materials, including but not limited to lithium ion permeable metal oxides, lithium ion permeable metal fluorides, lithium ion permeable carbon, and lithium ion permeable polymers.

[0064] In some embodiments, the negative electrode material has pores, and the total pore volume of the negative electrode material is 0.001 cm 3 / g to 0.1 cm 3 / g. Specifically, it can be 0.001 cm 3 / g, 0.005 cm 3 / g, 0.006 cm 3 / g, 0.007 cm 3 / g, 0.01 cm 3 / g, 0.02 cm 3 / g, 0.03 cm 3 / g, 0.04 cm 3 / g, 0.05 cm 3 / g, 0.08 cm 3 / g, or 0.1 cm 3 / g, etc., and of course, other values within the above ranges are also possible and are not limited herein. The appropriate amount of pores in the negative electrode material can provide space for the volume expansion of the silicon material, alleviate the expansion effect of the negative electrode material, improve the cycle stability of the negative electrode material, and also adsorb or accommodate a small amount of gas generated by the side reaction of the silicon material and the electrolyte, thereby improving the gas generation phenomenon of the negative electrode material.

[0065] In some embodiments, the volume distribution median particle size D50 of the negative electrode material is 5 μm to 10 μm; specifically, it can be 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 9.5 μm, 10 μm, etc., and of course, other values within the above ranges are also possible and are not limited herein. In the present application, the average particle size of the negative electrode material is controlled within the above range, which is beneficial to improving the cycle performance of the lithium ion battery made of the negative electrode material.

[0066] In some embodiments, the powder conductivity of the negative electrode material under a pressure of 20 kN is 8 S / cm to 30 S / cm, and can be 8 S / cm, 10 S / cm, 12 S / cm, 15 S / cm, 18 S / cm, 20 S / cm, 25 S / cm, or 30 S / cm, etc., without being limited herein. By distributing the metal material and boron atoms in the carbon matrix, the present application is advantageous to increase the electronic conductivity of the carbon matrix, and improve the powder conductivity and fast charging performance of the negative electrode material.

[0067] In some embodiments, the specific surface area of the negative electrode material is <10 m 2 / g, and can be 9.9 m 2 / g, 9.8 m 2 / g, 9.5 m 2 / g, 9.0 m 2 / g, 8.5 m 2 / g, 8.0 m 2 / g, 7.0 m 2 / g, 6.0 m 2 / g, 5.0 m 2 / g, 4.0 m 2 / g, 3.0 m 2 / g, or 1.0 m 2 / g, etc., and can also be other values within the above range, without being limited herein. It can be understood that the specific surface area of the negative electrode material affects the contact area of the negative electrode material and the electrolyte. When the specific surface area of the negative electrode material is within the above range, the side reaction of the negative electrode material and the electrolyte is reduced, the consumption of active lithium ions is reduced, and the first coulombic efficiency of the negative electrode material is improved.

[0068] In some embodiments, the mass percentage of carbon elements in the negative electrode material is 35% to 55%. Specifically, the mass percentage of carbon elements in the negative electrode material can be 35%, 40%, 42%, 45%, 48%, 50%, 52%, 53%, or 55%, without being limited herein.

[0069] In some embodiments, the mass percentage of oxygen elements in the negative electrode material is <4%, and specifically, the mass percentage of oxygen elements in the negative electrode material can be 3.9%, 3.8%, 3.7%, 3.5%, 3.0%, 2.9%, 2%, or 1%, without being limited herein.

[0070] In a second aspect, the present application provides a preparation method of a negative electrode material, as shown in FIG. 2, comprising the following steps:

[0071] Step S10, preparing a first precursor, the first precursor comprising a porous carbon material and a metal borate salt distributed in the porous carbon material;

[0072] Step S20, heating the first precursor to a first holding stage, and continuing to heat to a second holding stage to obtain a second precursor, wherein in the first holding stage, the metal borate salt is thermally decomposed to obtain a metal material, and in the second holding stage, boron atoms are doped into the porous carbon material;

[0073] Step S30, performing silicon deposition on the second precursor to obtain a silicon-based inner core;

[0074] Step S40, coating the silicon-based inner core to obtain the negative electrode material.

[0075] In the above scheme, by preparing the first precursor, the metal borate salt can be distributed in the porous carbon material, and then heating treatment is performed. In the first holding stage, the metal borate salt is thermally decomposed to obtain a metal material and borane. Since the boiling point of borane is low, as the heating temperature rises to the second holding stage, part of the borane volatilizes, and part of the borane is doped into the porous carbon material to obtain the second precursor. The second precursor includes a carbon matrix and a metal material distributed in the carbon matrix. Boron atoms are doped into the carbon matrix, and the boron atoms and carbon atoms form a P-pi conjugate system, which increases the electron orbit of the conjugate system and enhances the electron flow in the carbon matrix, thereby enhancing the conductivity of the negative electrode material. Then, the second precursor is subjected to silicon deposition treatment, and the silicon source gas enters the pores of the carbon matrix to form a silicon material. During the silicon deposition process, part of the silicon material is connected with the metal material in the pores of the carbon matrix, so that the conductivity of the negative electrode material is enhanced. Finally, the second precursor with deposited silicon material is subjected to coating treatment, so that a coating layer is formed on the surface of the negative electrode material. The existence of the coating layer can reduce the specific surface area of the negative electrode material, reduce the side reaction between the active material and the electrolyte, and improve the first coulomb efficiency and safety of the negative electrode material. In this application, the three-dimensional conductive network formed by the coating layer, the carbon matrix and the metal material can greatly enhance the conductivity of the silicon material, so that the negative electrode material prepared by the application has high conductivity, high first coulomb efficiency and excellent fast charging performance.

[0076] The preparation method of the application will be specifically described below in combination with examples:

[0077] Step S10, preparing a first precursor, the first precursor including a porous carbon material and a metal borate salt distributed in the porous carbon material.

[0078] In some embodiments, the total pore volume of the porous carbon material is 0.6 cm 3 / g to 1.0 cm 3 / g. Specifically, the pore volume of all pores in the porous carbon material can be 0.6 cm 3 / g, 0.7 cm 3 / g, 0.8 cm 3 / g, 0.9 cm 3 / g or 1.0 cm3 / g, of course, can also be 0.6 cm 3 / g~1.0 cm 3 / g, and other values between them are not limited herein.

[0079] In some embodiments, the volume distribution median particle size D50 of the porous carbon material is 5.5 μm~10.5 μm, and can specifically be 5.5 μm, 5.8 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm or 10.5 μm, and of course, can also be other values within the above range, which are not limited herein.

[0080] In some embodiments, the metal boron salt includes at least one of sodium borohydride, lithium borohydride, magnesium borohydride, lithium triethylborohydride, and lithium borate.

[0081] In some embodiments, the mass ratio of the porous carbon material to the metal boron salt is 100:(8~20), and the mass ratio can specifically be 100:8, 100:10, 100:12, 100:15, 100:18 or 100:20, and of course, can also be other values within the above range, which are not limited herein. When the mass ratio is too large, it means that the amount of the metal boron salt added is too small, and the prepared negative electrode material has less metal material, so that the space for accommodating the silicon material increases, the specific capacity of the negative electrode material increases, but the expansion effect of the silicon material intensifies, the consumed active lithium ions increase in the charge and discharge cycle process, and the first coulombic efficiency of the negative electrode material decreases. When the mass ratio is too small, it means that the amount of the metal boron salt added is too large, and the prepared negative electrode material has more metal material, so that the space occupied by the metal material in the carbon matrix increases, and the space for accommodating the silicon material decreases, and the specific capacity of the negative electrode material decreases. Moreover, the increase of the mass ratio of the metal material also increases the risk of spontaneous combustion of the negative electrode material, and reduces the safety.

[0082] In some embodiments, the step S10 specifically includes: mixing and stirring the porous carbon material and the metal boron salt solution uniformly, and then performing rotary evaporation to obtain the first precursor.

[0083] In some embodiments, the metal boron salt solution includes a solvent, and the solvent includes at least one of diethyl ether, liquid ammonia, and anhydrous ethanol.

[0084] In some embodiments, the temperature of the rotary evaporation can be 50℃~150℃, and can specifically be 50℃, 70℃, 80℃, 90℃, 100℃, 120℃ or 150℃, and of course, can also be other values within the above range, which are not limited herein.

[0085] In some embodiments, the mixing and the rotary evaporation are both performed under a protective gas.

[0086] Step S20, heating the first precursor to a first holding stage, and then heating to a second holding stage to obtain a second precursor, wherein in the first holding stage, the metal borate salt is thermally decomposed to obtain a metal material, and in the second holding stage, boron atoms are doped into the porous carbon material.

[0087] In some embodiments, the temperature of the first holding stage is 300-500°C, and the holding time is 1-2h. Specifically, the temperature of the first holding stage can be 300°C, 320°C, 350°C, 400°C, 420°C, 450°C, 480°C, and 500°C, and the time can be 1h, 1.2h, 1.3h, 1.5h, 1.6h, 1.7h, 1.8h, and 2h, and other values within the range can also be used, which can be selected according to actual needs, and are not limited herein.

[0088] In some embodiments, the temperature of the second holding stage is 600-850°C, and the holding time is 1-4h. Specifically, the temperature of the second holding stage can be 600°C, 650°C, 700°C, 750°C, 800°C, 820°C, and 850°C, and the time can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 3.8h, and 4h, and other values within the range can also be used, which can be selected according to actual needs, and are not limited herein.

[0089] In some embodiments, the first holding stage and the second holding stage are carried out under a protective gas. The protective gas includes at least one of nitrogen, helium, neon, argon, and krypton, which can be selected according to actual needs, and are not limited herein.

[0090] In some embodiments, the flow rate of the protective gas is 2-200L / min, and can be 2L / min, 5L / min, 10L / min, 20L / min, 50L / min, 70L / min, 80L / min, 90L / min, 100L / min, 150L / min, or 200L / min, and other values within the range can also be used, which can be selected according to actual needs, and are not limited herein.

[0091] In some embodiments, after the protective gas is introduced, air is removed, and the time for removing the air is 0.5-2h.

[0092] In some embodiments, the heating rate is 2-100°C / h, and can be 2°C / h, 5°C / h, 8°C / h, 10°C / h, 20°C / h, 40°C / h, 50°C / h, 80°C / h, or 100°C / h, and other values within the range can also be used, which can be selected according to actual needs, and are not limited herein.

[0093] The application controls the temperature and time of the first and second holding stages, so that the metal borate salt can be fully decomposed to form a metal material, and the boron atoms can be doped into the porous carbon material.

[0094] In some embodiments, at least part of the boron atoms are distributed on the pore walls of the porous carbon material.

[0095] In step S30, the second precursor is subjected to silicon material deposition to obtain a silicon-based inner core.

[0096] In some embodiments, the silicon material deposition on the second precursor specifically includes introducing a silicon source gas to perform gas-phase silicon deposition.

[0097] In some embodiments, the silicon source gas includes at least one of monosilane, disilane, monochlorosilane, dichlorosilane, trichlorosilane, and tetrachlorosilane. It should be noted that when the silicon source gas is monosilane, disilane, monochlorosilane, or dichlorosilane, it is gaseous at room temperature; when the silicon source gas is trichlorosilane or tetrachlorosilane, it is liquid at room temperature, and the liquid silicon source will be gasified into a gaseous silicon source during the gas-phase deposition process.

[0098] In some embodiments, the flow rate of the silicon source gas is 5 L / min to 200 L / min, and can specifically be 5 L / min, 8 L / min, 10 L / min, 12 L / min, 15 L / min, 18 L / min, 20 L / min, 50 L / min, 80 L / min, 100 L / min, or 200 L / min, etc., which are not limited herein.

[0099] In some embodiments, the temperature for silicon deposition is 500°C to 700°C, and can specifically be 500°C, 550°C, 600°C, 620°C, 650°C, 680°C, or 700°C, etc., or other values within the range, which can be selected according to actual needs, and are not limited herein.

[0100] In some embodiments, the time for silicon deposition is 2 h to 8 h, and can specifically be 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, or 8 h, etc., or other values within the range, which can be selected according to actual needs, and are not limited herein.

[0101] It can be understood that the process conditions for gas-phase silicon deposition, such as the deposition temperature, the flow rate of the silicon source gas, and the deposition time, will all affect the deposition of the silicon material in the pores of the porous carbon material. Controlling the temperature, the flow rate of the silicon source gas, and the time for gas-phase silicon deposition within the above ranges can ensure that the silicon source gas does not decompose and deposit before entering the pores of the carbon material, and quickly decomposes and deposits after entering the pores.

[0102] In step S40, the silicon-based core is coated to obtain the negative electrode material.

[0103] In some embodiments, the carbon coating specifically includes introducing a gas-phase carbon source into the silicon deposition product to perform gas-phase carbon coating treatment to obtain the negative electrode material.

[0104] In some embodiments, the gas-phase carbon source includes at least one of methane, ethane, propane, ethylene, acetylene, propylene, cyclopentane, cyclohexane, gaseous benzene, gaseous toluene, and gaseous xylene.

[0105] In some embodiments, the flow rate of the gas-phase carbon source is 10 L / min to 100 L / min, and can specifically be 10 L / min, 12 L / min, 15 L / min, 18 L / min, 20 L / min, 25 L / min, 50 L / min, 60 L / min, 80 L / min, or 100 L / min, etc., which is not limited herein.

[0106] In some embodiments, the carbon coating temperature is 500°C to 800°C, and can specifically be 500°C, 550°C, 600°C, 620°C, 650°C, 680°C, 700°C, 750°C, or 800°C, etc., or other values within the range, which can be selected according to actual needs, and is not limited herein.

[0107] In some embodiments, the carbon coating time is 2 h to 8 h, and can specifically be 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, or 8 h, etc., or other values within the range, which can be selected according to actual needs, and is not limited herein.

[0108] In other embodiments, the silicon-based core can also be carbon-coated by using a solid-phase carbon coating process, which is not limited herein.

[0109] In a third aspect, the embodiments of the present application also provide a battery. FIG. 3 is a schematic diagram of a discharging state of a battery provided by the embodiments of the present application. As shown in FIG. 3, the battery includes a shell and an electrode assembly. The electrode assembly includes a positive electrode sheet 1, a negative electrode sheet 2, and a separator 3. The separator 3 is arranged between the positive electrode sheet 1 and the negative electrode sheet 2. The electrode assembly can be a stacked structure, which is formed by alternately stacking the positive electrode sheet 1, the separator 3, and the negative electrode sheet 2 in sequence. In other embodiments, the electrode assembly can also be a wound structure, which is formed by winding the positive electrode sheet, the separator, and the negative electrode sheet in sequence after being stacked in sequence.

[0110] In some embodiments, the positive electrode sheet 1 includes a positive electrode current collector 101 and a positive electrode active layer 102 arranged on at least one surface of the positive electrode current collector 101.

[0111] In some embodiments, the positive current collector 101 can use an aluminum foil or a nickel foil, or the like, and can also be any composite current collector disclosed in the prior art, such as but not limited to a current collector formed by combining the aforementioned conductive foil (aluminum foil or nickel foil, or the like) and a polymer substrate. The positive active layer 102 contains a positive active material, which includes a compound that reversibly intercalates and deintercalates metal ions.

[0112] In some embodiments, the positive active material can include a lithium transition metal composite oxide, a sodium transition metal composite oxide, or the like. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel.

[0113] In some embodiments, the positive active material can include, but is not limited to, at least one of lithium cobaltate (LiCoO2), lithium nickel manganese cobalt ternary material (NCM), lithium manganate (LiMn2O4), lithium nickel cobalt manganese oxide (LiNi0.5Mn1.5O4), or lithium iron phosphate (LiFePO4). 4) 0.5 1.5 In some embodiments, the positive active material can include, but is not limited to, at least one of lithium cobaltate (LiCoO2), lithium nickel manganese cobalt ternary material (NCM), lithium manganate (LiMn2O4), lithium nickel cobalt manganese oxide (LiNi0.5Mn1.5O4), or lithium iron phosphate (LiFePO4).

[0114] In some embodiments, the negative electrode sheet 2 includes a negative current collector 201 and a negative active material layer 202 provided on at least one surface of the negative current collector.

[0115] In some embodiments, the negative current collector 201 can use at least one of a copper foil, a nickel foil, a stainless steel foil, a titanium foil, or a carbon-based current collector, or the like, and can also be any composite current collector disclosed in the prior art, such as but not limited to a current collector formed by combining the aforementioned conductive foil and a polymer substrate. The negative active material layer 202 includes a negative material, which is the negative material of the first aspect described above or the negative material obtained by the preparation method described above.

[0116] The battery provided by the embodiments of the present application has the advantages of high capacity, high initial efficiency, long cycle life, excellent rate performance, and low swelling. The battery can be a lithium ion battery, a sodium ion battery, a solid electrolyte battery, or the like, without limitation.

[0117] The embodiments of the present application are further described below in multiple embodiments. The embodiments of the present application are not limited to the following specific embodiments. Within the scope of the same rights, appropriate changes can be made.

[0118] Test method:

[0119] 1. Mass percentage content of metal elements, boron elements, and silicon elements in the negative material:

[0120] ​​The negative electrode material is subjected to hot digestion with aqua regia using an Agilent 5800 device using the method of GB / T 24533-2019 "Lithium ion battery graphite negative electrode material". After constant volume, the mass percentage contents of metal elements, boron elements and silicon elements are tested by ICP. The aqua regia is prepared from concentrated hydrochloric acid and concentrated nitric acid in a volume ratio of 3:1. The concentration of the concentrated hydrochloric acid used for preparation is 12 mol / L, and the concentration of the concentrated nitric acid is 14.5 mol / L.

[0121] 2. Specific surface area, pore volume test method:

[0122] The iPore620 pore size tester of Linkchem and the BET pore size distribution test method are used. The pore size distribution data of the material are obtained by DFT simulation analysis using the isothermal adsorption characteristic curve of nitrogen, and then the average pore size, pore volume and BET specific surface area of the material are obtained.

[0123] 3. Particle size test method of negative electrode material:

[0124] The particle size test method refers to GB / T 19077-2016. The volume-based cumulative particle size distribution of the negative electrode material particle size distribution is measured by a Malvern laser particle size analyzer (Mastersizer3000) and a laser diffraction method. D50 represents the particle size corresponding to the cumulative particle size distribution percentage of 50%.

[0125] 4. Type and average particle size of silicon material:

[0126] The type of silicon material is determined by measuring the diffraction peak using an X-ray diffractometer (XRD).

[0127] The silicon material in the negative electrode material is observed by field emission scanning electron microscopy or transmission electron microscopy. The particle size of 5-10 silicon materials is directly measured by a scale, and the average particle size of the silicon material is taken as the final average particle size.

[0128] 5. Powder conductivity test:

[0129] The conductivity under 20KN pressure is tested by using the MCP-PD51 powder resistance test system of Mitsubishi Chemical, Japan, and the volume resistivity of the sample is measured by the four-probe method. The resistance of the powder can be measured by using the instrument, and then the conductivity and resistivity of the powder are automatically calculated by the computer.

[0130] 6. Test method of coating thickness:

[0131] In the electron microscope image taken by the cold field emission scanning electron microscope of Hitachi, Japan, the coating layer of a single particle is measured using the graphic analysis software of the device. The coating thickness of 100 single particles is continuously measured, and the average value is calculated. The average value is the coating thickness.

[0132] 7. Test of the mass percentage content of oxygen element in the negative electrode material:

[0133] According to GB / T 11261-2006, using German Velder oxygen-nitrogen-hydrogen element analyzer ONH 2000, the sample is melted under flux wrapping in an inert atmosphere, the oxygen element contained therein is reduced to carbon dioxide by carbon in the graphite crucible, the generated carbon dioxide enters the infrared detector with the carrier gas, and the mass percentage content of oxygen element is calculated by quantitative statistical calculation of the change of carbon dioxide infrared signal.

[0134] 8. Test of the mass percentage content of carbon element in the negative electrode material:

[0135] Using German Bruker / German Ert infrared carbon-sulfur analyzer G4ICARUS HF / CS-i, the sample is burned in an oxygen-rich state at high temperature, the carbon element contained therein is oxidized to carbon dioxide, and enters the infrared detector with the carrier gas, and the mass percentage content of carbon element is calculated by quantitative statistical calculation of the change of carbon dioxide signal infrared absorption wavelength intensity.

[0136] 9. Electrical performance test:

[0137] The following method is used to test the button cell: the negative electrode slurry is prepared according to the mass ratio of the negative electrode material, conductive carbon black and acrylonitrile multi-component copolymer (LA133) of 70:15:15, coated on a copper foil with a thickness of d0, dried to form a negative electrode sheet, and the electrode sheet thickness is d1. A lithium metal sheet is used as the counter electrode to assemble a button cell in an Ar-filled glove box. The button cell is charged and discharged at a current density of 0.1C in the charge-discharge interval of 0.01-5V, and the first reversible specific capacity and the first coulombic efficiency of the button cell are obtained.

[0138] The button cell is repeatedly charged and discharged 50 times at a current density of 3C in the charge-discharge interval of 0.01V-5V, and the capacity retention rate and the electrode sheet thickness d2 after 50 cycles of the battery are obtained, and the electrode sheet expansion rate = (d2-d0) / (d1-d0)*100%.

[0139] Example 1:

[0140] (1) In an argon atmosphere, 1Kg of porous carbon with a pore volume of 0.6cm 3 / g and a particle size of D50=7.2um is mixed and stirred with a lithium borohydride ether solution containing 50g of lithium element (the mass ratio of porous carbon to lithium borohydride is 70:11), and then rotary evaporation is carried out at 80℃ to remove the ether solution, so that the lithium borohydride is loaded into the pores of the porous carbon to obtain a first precursor.

[0141] (2) Put the first precursor into a deposition furnace, introduce argon gas to remove air, and then heat to a first holding stage at 450°C for 2h, and then continue to heat to a second holding stage at 800°C for 2h, to obtain a second precursor, which comprises a carbon matrix doped with boron elements and lithium metal material distributed in the carbon matrix.

[0142] (3) Reduce the second precursor to 600°C for gas-phase silicon deposition, introduce 50L / min of silane for deposition for 6h, to obtain a silicon-based inner core, which comprises a carbon matrix doped with boron elements, lithium metal material and silicon material distributed in the carbon matrix.

[0143] (4) Put the silicon-based inner core into a vacuum distillation furnace, and heat to 650°C, introduce 50L / min of methane gas for gas-phase carbon coating for 4h, to obtain the negative electrode material.

[0144] The negative electrode material prepared by the embodiment of the present application comprises an inner core and a coating layer located on at least part of the surface of the inner core, the inner core comprises a carbon matrix, an active material and boron elements distributed in the carbon matrix, the active material comprises silicon material and metal material, and at least part of the silicon material and the metal material are connected.

[0145] Other embodiments are different from the preparation process of embodiment 1 as shown in Table 1.

[0146] Comparative example 1:

[0147] (1) Heat 1Kg of porous carbon with a pore volume of 0.6cm 3 / g and a particle size of D50=7.2um to 600°C for gas-phase silicon deposition, introduce 50L / min of silane for deposition for 6h, to obtain a silicon-based inner core, which comprises a carbon matrix and silicon material distributed in the carbon matrix.

[0148] (2) Put the precursor into a vacuum distillation furnace, and heat to 650°C, introduce 50L / min of methane gas for gas-phase carbon coating for 4h, to obtain the negative electrode material.

[0149] The negative electrode material prepared by comparative example 1 comprises an inner core and a coating layer located on at least part of the surface of the inner core, the inner core comprises a carbon matrix and silicon material distributed in the carbon matrix.

[0150] Table 1. Process parameters for preparing the negative electrode material

[0151] Table 2. Physicochemical parameters of the negative electrode material

[0152] Table 3 Physico-chemical parameters of the batteries

[0153] The negative electrode material prepared according to Examples 1-28 comprises an inner core and a coating layer on at least part of the surface of the inner core. The inner core comprises a carbon matrix and active material and boron atoms distributed in the carbon matrix. Since the boron atoms have an outer P empty orbital, the P empty orbital can form a P-π conjugate system with the π-π conjugate system of the carbon matrix, increase the electron orbit of the conjugate system, and enhance the electron flow in the carbon matrix, thereby enhancing the electrical conductivity of the negative electrode material. In addition, since the metal material has excellent electrical conductivity, the connection of the metal material and the silicon material can enhance the electrical conductivity of the negative electrode material. The inner core has a coating layer on at least part of the surface, and the presence of the coating layer can reduce the specific surface area of the negative electrode material, reduce the occurrence of side reactions between the active material and the electrolyte, and improve the first coulombic efficiency and safety of the negative electrode material. In this application, the three-dimensional conductive network formed by the coating layer, the boron-doped carbon matrix, and the metal material can greatly improve the electrical conductivity of the silicon material, and the negative electrode material has high electrical conductivity, high first coulombic efficiency, and excellent fast-charging performance.

[0154] According to the test data of Example 3 and Comparative Example 1, it can be known that in the preparation process of Comparative Example 1, no metal borate salt is added, and the prepared negative electrode material comprises an inner core and a coating layer on the surface of the inner core. The inner core comprises a carbon matrix and silicon material distributed in the carbon matrix, and the electrical conductivity of the negative electrode material is greatly reduced.

[0155] The above examples according to the drawings illustrate the structure, features and effects of the present application. The above description is only the preferred embodiment of the present application, but the present application is not limited by the drawings. Any changes or modifications made in accordance with the concept of the present application, or equivalent embodiments with equivalent changes, shall be within the scope of the present application.

Claims

1. A negative electrode material, characterized by, The negative electrode material comprises an inner core and a coating layer located on at least part of the surface of the inner core, the inner core comprises a carbon matrix, an active material distributed in the carbon matrix, and boron element, the active material comprises a silicon material and a metal material, and at least part of the silicon material and the metal material are connected.

2. The negative electrode material according to claim 1, characterized in that, The mass percentage content of the metal element in the negative electrode material is A%, the mass percentage content of the silicon element in the negative electrode material is B%, and the negative electrode material satisfies 0.03 3. The negative electrode material according to claim 2, characterized in that, 1.4 4. The negative electrode material of claim 1, wherein, The metal material comprises at least one of lithium particles, magnesium particles, and sodium particles.

5. The negative electrode material of claim 1, wherein, The mass percentage content of the boron element in the negative electrode material is C%, and 0.4 6. The negative electrode material of claim 1, wherein, The silicon material comprises at least one of silicon element, silicon oxide, and silicon alloy.

7. The negative electrode material according to claim 6, characterized in that, The negative electrode material has at least one of the following characteristics: (1) the silicon material comprises a silicon oxide having a general formula of SiO x wherein 0.5≤x<2; (2) The silicon material comprises crystalline silicon and / or amorphous silicon; (3) The average particle size of the silicon material is 1 nm to 50 nm.

8. The negative electrode material of claim 1, wherein, The carbon matrix comprises at least one of amorphous carbon, graphitized carbon, mesocarbon microbeads, and carbon gel.

9. The negative electrode material of claim 1, wherein, The negative electrode material has pores, and the total pore volume of the negative electrode material is 0.001 cm 3 / g to 0.1 cm 3 / g.

10. The negative electrode material of claim 1, wherein, The thickness of the coating layer is 5 nm to 20 nm; and / or the coating layer comprises at least one of carbon, nitride, metal oxide, metal fluoride, metal oxyfluoride, and polymer.

11. The negative electrode material according to any one of claims 1 to 10, characterized in that, The specific surface area of the negative electrode material is less than 10 m 2 / g.

12. The negative electrode material according to any one of claims 1 to 10, characterized by, The volume distribution median particle size D50 of the negative electrode material is 5 μm to 10 μm.

13. The negative electrode material according to any one of claims 1 to 10, characterized by, The powder conductivity of the negative electrode material under a pressure of 20 KN is 8 S / cm to 30 S / cm.

14. The negative electrode material according to any one of claims 1 to 10, characterized by, The mass percentage content of oxygen element in the negative electrode material is less than 4%; and / or the mass percentage content of carbon element in the negative electrode material is 35% to 55%.

15. A battery, characterized by The battery comprises the negative electrode material according to any one of claims 1 to 14.

Images