Negative electrode material and preparation method thereof, secondary battery and electronic device

Abstract

A negative electrode material and a preparation method thereof, a secondary battery and an electronic device, the negative electrode material includes silicon carbon particles, the cross section of the silicon carbon particles includes a surface region and an internal region, the surface region contains a first substance, and the first substance has ionic conductivity; a hole area ratio of the surface region is greater than a hole area ratio of the inner region. By regulating and controlling the pore area distribution of the surface area and the internal area of the silicon-carbon particles to be matched with the first substance, the expansion of the silicon material can be effectively buffered, an efficient lithium ion path is constructed in the surface area, and the dynamic performance and the expansion inhibition performance of the secondary battery are improved.

Description

Technical Field

[0001] The present application belongs to the field of energy storage technology, and specifically relates to a negative electrode material and a preparation method thereof, a secondary battery and an electronic device. Background Art

[0002] As a rechargeable energy storage device, secondary batteries play a vital role in modern society and are widely used in portable electronic devices, electric vehicles, energy storage systems and other fields. The basic principle is to store and release electrical energy through the process of lithium ion insertion and extraction between positive and negative electrode materials. In secondary batteries, the negative electrode material, as a carrier of lithium ions, plays a decisive role in the overall performance of the battery. An ideal negative electrode material should have high specific capacity, good cycle stability, high coulombic efficiency, and excellent electronic and ionic conductivity.

[0003] However, with the continuous development of secondary battery technology, improving its kinetic performance and inhibiting expansion performance have become technical problems that need to be solved urgently. Among them, the improvement of kinetic performance is directly related to the charge and discharge rate and efficiency of the battery, which is crucial to meet the needs of fast charging and high-power applications. The expansion problem, especially in silicon-containing battery systems, is caused by the precipitation and dissolution reactions of silicon-containing materials during the charging and discharging process, which will lead to significant changes in the volume of the negative electrode, thereby causing an increase in the internal stress of the battery, and may even cause safety problems such as battery short circuit and failure. Therefore, how to improve the kinetic performance and inhibit expansion performance of secondary batteries is a key issue in promoting the continuous advancement and widespread application of secondary battery technology. Summary of the invention

[0004] In view of this, the present application provides a negative electrode material and a preparation method thereof, a secondary battery and an electronic device. By regulating the pore area of ​​the surface area and the internal area of ​​the silicon-carbon particles and coordinating with the first substance, it is possible to buffer the expansion of the silicon material and construct an efficient lithium ion path in the surface area, thereby improving the kinetic performance and inhibiting expansion performance of the secondary battery.

[0005] In the first aspect, the present application provides a negative electrode material, including silicon-carbon particles, the cross-section of the silicon-carbon particles includes a surface area and an internal area, the surface area contains a first substance, and the first substance has ion conductivity; the first substance contains an M element, and the M element is selected from at least one of an S element, an N element, an La element, an Ti element, an Zr element, an Al element, and an P element; the pore area ratio of the surface area is greater than the pore area ratio of the internal area; the surface area refers to the area from 0nm to 500nm away from the surface of the silicon-carbon particles, and the internal area refers to the area from 600nm to 1200nm away from the surface of the silicon-carbon particles. The present application controls the pore area ratio of the surface area in the cross section of the silicon-carbon particle to be greater than the pore area ratio of the internal area, that is, controls the pores in the surface area of ​​the silicon-carbon particle to have a larger pore size. When nano-silicon is deposited, silane is difficult to adsorb in the larger pores. At the same time, the smaller specific surface area caused by the large pore size also reduces the contact between the surface area and the silane gas, which is not conducive to the attachment and deposition of nano-silicon. Therefore, the deposition amount of nano-silicon in the surface area can be reduced, and more nano-silicon is deposited in the internal area deep in the porous carbon, which is beneficial to improve the buffering effect on the volume expansion of nano-silicon during lithium insertion and extraction, improve the inhibitory effect on the expansion of the negative electrode material, reduce the side reaction with the electrolyte, and reduce the damage to the surface of the silicon-carbon particles; and the first substance with ion conductivity is easily combined in the larger pores in the surface area, and a continuous and efficient lithium ion path can be constructed in the surface area of ​​the silicon-carbon particle, thereby improving the kinetic performance of the negative electrode material. The lithium ion path in the surface area also helps to disperse the expansion stress, while avoiding the violent side reactions caused by the direct contact between the nano-silicon and the electrolyte, reducing the accumulation of by-products, so that the secondary battery exhibits excellent rate performance and expansion inhibition performance.

[0006] In some embodiments, the silicon carbon particles contain porous carbon, and the porous carbon includes type I pores and type II pores. The pore diameter of the type I pores is D1 nm, 0.5≤D1<2, and the pore diameter of the type II pores is D2 nm, 2≤D1≤15; based on the sum of the pore volume of the type I pores and the pore volume of the type II pores, the pore volume proportion of the type II pores is P%, 2≤P≤20. The present application regulates the sum of the pore volume of the first type of pores and the pore volume of the second type of pores in the porous carbon. The pore volume proportion of the second type of pores is within the above range, that is, the pore volume proportion of the first type of pores is 80% to 98%, and the pore volume proportion of the first type of pores is much higher than that of the second type of pores, which can provide a higher silicon deposition capacity, thereby increasing the lithium storage capacity of silicon-carbon particles; combined with the fact that the pore area proportion of the surface area is greater than that of the internal area, it is beneficial for nano-silicon to be deposited more in the deep area exceeding 500nm inside the porous carbon, thereby improving the buffering effect on the volume expansion of nano-silicon, and the first substance is deposited more in the surface area, thereby improving the conductivity of the ion path in the surface area, thereby further improving the rate performance and expansion inhibition performance of the secondary battery.

[0007] In some embodiments, 4≤P≤15. When the porous carbon satisfies this condition, the rate performance and the expansion suppression performance of the secondary battery can be further improved.

[0008] In some embodiments, the first material is selected from lithium aluminum oxide, lithium phosphate, Li x1 PO y1 N z1 , where 2.8≤x1≤3.3, 3.0≤y1≤3.8, 0.16≤z1≤0.46, Li7La3Zr2O 12 , Li 3x2 La 2 / 3-x2 TiO3, where 0.06≤x2≤0.16, lithium thiophosphate, Li 1+x3 Al x3 Ti 2-x3 (PO4)3, wherein 0≤x3≤0.7, at least one of Li6PS5Cl. The first substance has high ionic conductivity and can form a continuous and efficient lithium ion path in the surface area of ​​the silicon-carbon particles, thereby shortening the diffusion path of lithium ions in the silicon-carbon particles, accelerating the speed of lithium ion insertion and extraction, and can also serve as a buffer layer to reduce the volume expansion of silicon-carbon particles and improve the wettability of the electrolyte to the silicon-carbon particles, thereby facilitating further improvement of the rate performance and expansion inhibition performance of the secondary battery.

[0009] In some embodiments, based on the mass of the silicon-carbon particles, the mass percentage of the M element is C%, 0.3≤C≤6; preferably, 0.6≤C≤4. When the mass percentage of the M element meets the above range, the conduction path and structural stability of the lithium ion path can be further optimized, the diffusion rate of lithium ions in the surface area of ​​the silicon-carbon particles can be increased, and the rate performance and expansion inhibition performance of the secondary battery can be improved.

[0010] In some embodiments, the silicon-carbon particles include porous carbon and nano-silicon located in the pores of the porous carbon; a carbon layer is provided on the surface of the silicon-carbon particles, and the thickness of the carbon layer is T nm, 5≤T≤80; preferably, 10≤T≤50. The present application controls at least part of the surface of the silicon-carbon particles to have a carbon layer, which can form an excellent electron path with the internal porous carbon, and can improve the ionic conductivity and electronic conductivity of the silicon-carbon particles in combination with the first substance, and can improve the mechanical strength and toughness of the silicon-carbon particles, improve the buffering effect on the expansion of nano-silicon during the charge and discharge process, and improve the structural stability of the silicon-carbon particles, thereby further improving the rate performance and expansion inhibition performance of the secondary battery.

[0011] In some embodiments, 20≤C×T≤60. When 20≤C×T≤60 is satisfied, the coordination effect between the carbon layer and the first material can be enhanced, and the rate performance and expansion suppression performance of the secondary battery can be further improved.

[0012] The present application also provides a method for preparing the aforementioned negative electrode material, which comprises at least the following steps:

[0013] Step S1, calcining the precursor material at T1°C in an inert gas atmosphere for t1 hours to obtain a carbonized material; 550≤T1≤1600, 2≤t1≤10;

[0014] Step S2, after the carbonized material is crushed, a first activated gas is introduced at T2°C and reacted for t2 hours to obtain a first activated material; 780≤T2≤950, 8≤t2≤20; the first activated gas is at least one of water vapor and carbon dioxide;

[0015] Step S3, heating the first activated material to T3°C in an inert gas atmosphere, introducing a second activated gas, and reacting for t3 hours to obtain porous carbon; 850≤T3≤1300, 2≤t3≤8; the second activated gas is at least one of water vapor, carbon dioxide or oxygen;

[0016] Step S4, introducing silane gas into the porous carbon at T4°C and keeping the temperature for t4 hours to obtain silicon-precipitated particles; 380≤T4≤600, 2≤t4≤5;

[0017] Step S5, transferring the precipitated silicon particles to a dispersion medium in an inert gas protection atmosphere, adding an M element source and dispersing the particles, and then evaporating the dispersion medium in a vacuum environment to obtain silicon-carbon particles.

[0018] Based on the above scheme, the present application uses two activation treatments to make the pores in the surface area have a larger pore size, thereby controlling the pore area ratio of the surface area of ​​the silicon-carbon particles to be greater than the pore area ratio of the internal area, and arranging a first substance including the M element in the surface area, which can construct an efficient lithium ion pathway and improve the buffering effect on the volume expansion of nano-silicon, thereby further improving the rate performance and expansion inhibition performance of the secondary battery.

[0019] In some embodiments, the preparation method further comprises: step S6, heating the silicon-carbon particles to T5°C in an inert gas atmosphere, introducing acetylene gas, and keeping the temperature for t5 hours; 500≤T5≤700, 2≤t5≤8. Through step S4, a carbon layer can be provided on the surface of the silicon-carbon particles, which can further improve the rate performance and expansion inhibition performance of the secondary battery after being combined with the first substance.

[0020] The present application also provides a secondary battery, comprising a positive electrode, a negative electrode and an electrolyte; the negative electrode comprises a negative electrode collector and a negative electrode material layer arranged on at least one surface of the negative electrode collector; the negative electrode material layer comprises the aforementioned negative electrode material or the negative electrode material prepared by the aforementioned preparation method.

[0021] In some embodiments, the electrolyte includes at least one of ethyl acetate or ethyl fluoroacetate; based on the mass of the electrolyte, the electrolyte satisfies at least one of the following conditions:

[0022] (1) the mass proportion of ethyl acetate is E%, 1≤E≤20; preferably, 5≤E≤16;

[0023] (2) The mass percentage of ethyl fluoroacetate is F%, 15≤F≤50; preferably, 20≤F≤30.

[0024] Based on the above scheme, the M element in the first substance can induce ethyl acetate and ethyl fluoroacetate to form a solid electrolyte interface film (SEI film) rich in inorganic substances on the surface of silicon-carbon particles, reduce the consumption of lithium ions in the electrolyte, and improve the compactness and stability of the SEI film, so as to buffer the volume expansion of silicon-carbon particles during the charging and discharging process, wherein ethyl fluoroacetate can further improve the flexibility of the SEI film and further adapt to the volume change of nano-silicon. The SEI film rich in Li element is also conducive to improving the interface compatibility between the negative electrode and the electrolyte, improving the wettability of the electrolyte to the above silicon-carbon particles, and promoting the transmission of lithium ions at the interface between the silicon-carbon particles and the electrolyte, thereby improving the expansion inhibition performance and rate performance of the secondary battery.

[0025] In some embodiments, the electrolyte includes a first lithium salt, and the first lithium salt is selected from at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, or lithium trifluoromethylsulfonate; based on the mass of the electrolyte, the mass proportion of the first lithium salt is S1%, 0.01≤S1≤1. The present application provides more free lithium ions through the first lithium salt, which can further improve the ionic conductivity of the secondary battery system by cooperating with the first substance in the surface area of ​​the silicon-carbon particles, and is also beneficial to improve the wettability of the electrolyte to the silicon-carbon particles, and participate in the formation of a more stable LiF-rich SEI film on the surface of the silicon-carbon particles, buffering the volume expansion of the silicon-carbon particles, thereby further improving the expansion inhibition performance and rate performance of the secondary battery.

[0026] The present application further provides an electronic device, comprising the aforementioned secondary battery. Based on the aforementioned secondary battery, the electronic device of the present application can adapt to the conditions of rapid charge and discharge, and achieve excellent service life and safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a pore size distribution curve of porous carbon in a negative electrode material provided in Example 1-1 of the present application. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the present application more clear, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described here are only used to explain the present application and are not used to limit the present application.

[0029] In the first aspect, the present application provides a negative electrode material, including silicon-carbon particles, the cross-section of the silicon-carbon particles includes a surface area and an internal area, the surface area contains a first substance, and the first substance has ion conductivity; the first substance contains an M element, and the M element is selected from at least one of an S element, an N element, an La element, an Ti element, an Zr element, an Al element, and an P element; the pore area ratio of the surface area in the cross-section of the silicon-carbon particles is greater than the pore area ratio of the internal area; the surface area refers to the area from 0nm to 500nm away from the surface of the silicon-carbon particles, and the internal area refers to the area from 600nm to 1200nm away from the surface of the silicon-carbon particles. The present application controls the pore area ratio of the surface region to be greater than the pore area ratio of the internal region, that is, controls the pores in the surface region of the silicon-carbon particles to have a larger pore size. When nano-silicon is deposited, silane is difficult to adsorb in the larger pores. At the same time, the smaller specific surface area caused by the large pore size also reduces the contact between the surface region and the silane gas, which is not conducive to the attachment and deposition of nano-silicon. Therefore, the deposition amount of nano-silicon in the surface region can be reduced, and more nano-silicon is deposited in the internal region deep in the porous carbon, which is beneficial to improve the buffering effect on the volume expansion of nano-silicon during lithium insertion and extraction, improve the inhibitory effect on the expansion of the negative electrode material, reduce the side reaction with the electrolyte, and reduce the damage to the surface of the silicon-carbon particles; and the first substance with ion conductivity is easily combined in the larger pores in the surface region, and a continuous and efficient lithium ion path can be constructed in the surface region of the silicon-carbon particles, thereby improving the kinetic performance of the negative electrode material. The lithium ion path in the surface region also helps to disperse the expansion stress, while avoiding the violent side reactions caused by the direct contact between the nano-silicon and the electrolyte, reducing the accumulation of by-products, so that the secondary battery exhibits excellent rate performance and expansion inhibition performance.

[0030] In the present application, a thin slice sample of silicon carbon particles can be obtained by focused ion beam (FIB), the thickness of the thin slice sample is 50-100 nm, and then the thin slice sample is observed by transmission electron microscopy (TEM) to compare the pore area sizes of the surface area and the internal area.

[0031] In some embodiments, the silicon carbon particles include porous carbon, the porous carbon includes a type I pore and a type II pore, the pore size of the type I pore is D1 nm, 0.5≤D1<2, the pore size of the type II pore is D2 nm, 2≤D1≤15; based on the sum of the pore volume of the type I pore and the pore volume of the type II pore, the pore volume of the type II pore accounts for P%, 2≤P≤20. Preferably, 4≤P≤15. Exemplarily, P can be a value within the range of 2, 4, 5, 6, 9, 10, 11, 12, 14, 15, 17, 18, 19, 20 or any two thereof. The present application regulates the sum of the pore volume of the first type of pores and the pore volume of the second type of pores in the porous carbon. The pore volume proportion of the second type of pores is within the above range, that is, the pore volume proportion of the remaining first type of pores is 80% to 98%. The pore volume proportion of the first type of pores is much higher than the pore volume proportion of the second type of pores, which can provide a higher silicon deposition capacity, thereby increasing the lithium storage capacity of the silicon-carbon particles; combined with the fact that the pore area proportion of the surface area is greater than that of the internal area, it is beneficial for more nano-silicon to be deposited in the deep area exceeding 500nm inside the porous carbon, thereby improving the buffering effect on the volume expansion of nano-silicon, and the first substance is more deposited in the surface area, thereby improving the conductivity of the ion path in the surface area, thereby further improving the rate performance and expansion inhibition performance of the secondary battery.

[0032] In some embodiments, the first material is selected from lithium aluminum oxide, lithium phosphate, Li x1 PO y1 N z1 , where 2.8≤x1≤3.3, 3.0≤y1≤3.8, 0.16≤z1≤0.46, Li7La3Zr2O 12 , Li 3x2 La 2 / 3-x2 TiO3, where 0.06≤x2≤0.16, lithium thiophosphate, Li 1+x3 Al x3 Ti 2-x3 (PO4)3, wherein 0≤x3≤0.7, at least one of Li6PS5Cl. The first substance has high ionic conductivity and can form a continuous and efficient lithium ion path in the surface area of ​​the silicon-carbon particles, thereby shortening the diffusion path of lithium ions in the silicon-carbon particles, accelerating the speed of lithium ion insertion and extraction, and can also serve as a buffer layer to reduce the volume expansion of silicon-carbon particles and improve the wettability of the electrolyte to the silicon-carbon particles, thereby facilitating further improvement of the rate performance and expansion inhibition performance of the secondary battery.

[0033] In some embodiments, based on the mass of the silicon-carbon particles, the mass percentage of the M element is C%, 0.3≤C≤6; preferably, 0.6≤C≤4. Exemplarily, C can be a value in the range of 0.5, 0.7, 1.3, 2.4, 3.3, 4.1, 4.3, 5.5, 5.9, 6.0 or any two thereof. When the mass percentage of the M element satisfies the above range, the conduction path and structural stability of the lithium ion path can be further optimized, the diffusion rate of lithium ions in the surface area of ​​the silicon-carbon particles can be increased, and the rate performance and expansion inhibition performance of the secondary battery can be improved.

[0034] In some embodiments, the silicon-carbon particles include porous carbon and nano-silicon located in the pores of the porous carbon; a carbon layer is provided on the surface of the silicon-carbon particles, and the thickness of the carbon layer is T nm, 5≤T≤80; preferably, 10≤T≤50. Exemplarily, T can be a value within the range of 5, 8, 15, 22, 27, 31, 35, 44, 48, 53, 59, 66, 71, 80 or any two thereof. The present application controls at least part of the surface of the silicon-carbon particles to have a carbon layer, which can form an excellent electron path with the internal porous carbon, and can be combined with the first substance to improve the ionic conductivity and electronic conductivity of the silicon-carbon particles, and can improve the mechanical strength and toughness of the silicon-carbon particles, improve the buffering effect on the expansion of nano-silicon during the charge and discharge process, and improve the structural stability of the silicon-carbon particles, thereby further improving the rate performance and expansion inhibition performance of the secondary battery.

[0035] In some embodiments, 20≤C×T≤60. Exemplarily, the value of C×T is 20, 23, 25, 29, 33, 37, 40, 41, 43, 44, 46, 47, 48, 50, 51, 53, 55, 56, 57, 59, 60 or a value in the range of any two thereof. When the above range is met, the mutual coordination effect of the carbon layer and the first substance can be improved, and the rate performance and expansion inhibition performance of the secondary battery can be further improved.

[0036] The present application also provides a method for preparing the aforementioned negative electrode material, which comprises at least the following steps:

[0037] Step S1, calcining the precursor material at T1°C in an inert gas atmosphere for t1 hours to obtain a carbonized material; 550≤T1≤1600, 2≤t1≤10;

[0038] Step S2, after the carbonized material is crushed, a first activated gas is introduced at T2°C and reacted for t2 hours to obtain a first activated material; 780≤T2≤950, 8≤t2≤20; the first activated gas is at least one of water vapor and carbon dioxide;

[0039] Step S3, heating the first activated material to T3°C in an inert gas atmosphere, introducing a second activated gas, and reacting for t3 hours to obtain porous carbon; 850≤T3≤1300, 2≤t3≤8; the second activated gas is at least one of water vapor, carbon dioxide or oxygen;

[0040] Step S4, introducing silane gas into the porous carbon at T4°C and keeping the temperature for t4 hours to obtain silicon-precipitated particles; 380≤T4≤600, 2≤t4≤5;

[0041] Step S5, transferring the precipitated silicon particles to a dispersion medium in an inert gas protection atmosphere, adding an M element source and dispersing the particles, and then evaporating the dispersion medium in a vacuum environment to obtain silicon-carbon particles.

[0042] In some embodiments, the dispersion medium includes at least one of 1,2-dimethoxyethane, tetrahydrofuran, acetonitrile, ethyl propionate, ethyl acetate, 2-methyltetrahydrofuran, and ethanol.

[0043] In some exemplary embodiments, the preparation of porous carbon includes:

[0044] The precursor material is carbonized at 550-1600°C for 2-10 hours under a nitrogen atmosphere to obtain a carbonized material. The carbonized material is then placed in a reaction furnace, heated to 780-950°C, and then water vapor is introduced to form pores. After keeping the temperature for 8-20 hours, the first activated material is obtained. The first activated material is then heated to 850-1300°C under a nitrogen atmosphere, and then water vapor is introduced. After keeping the temperature for 2-8 hours, porous carbon is obtained. Through the two-step activation process, the pore area ratio of the surface area in the cross section of the silicon-carbon particles is controlled to be greater than the pore area ratio of the internal area.

[0045] In some embodiments, the precursor is selected from at least one of a biomass precursor, a sugar precursor, a synthetic resin precursor, or an asphalt precursor.

[0046] In some exemplary embodiments, the preparation of silicon carbon particles includes:

[0047] Place porous carbon in a fluidized bed device, introduce nitrogen into the interior to completely fluidize it, and then heat it to 380-600°C; for example, the heating rate is 5°C / min; after the temperature in the fluidized bed stabilizes, introduce silane gas, keep it warm for 2-5 hours, obtain silicon-precipitated particles, then switch to nitrogen and gradually cool to room temperature. Transfer the silicon-precipitated particles to anhydrous acetonitrile under nitrogen protection, add Li2S and P2S5 in a molar ratio of 7:3, stir evenly, and place it in a vacuum environment to heat and evaporate the solvent to obtain silicon-carbon particles.

[0048] Based on the above scheme, the present application uses two activation treatments to make the pores in the surface area have a larger pore size, thereby controlling the pore area ratio of the surface area in the cross section of the silicon-carbon particles to be greater than the pore area ratio of the internal area, and arranging a first substance including the M element in the surface area, which can construct an efficient lithium ion path and improve the buffering effect on the volume expansion of nano-silicon, thereby further improving the rate performance and expansion inhibition performance of the secondary battery.

[0049] In some exemplary embodiments, the preparation method further includes: step S6, heating the silicon-carbon particles to T6°C under nitrogen protection, then introducing acetylene gas, and keeping the temperature for t6h; 500≤T6≤700, 2≤t6≤8. Through step S6, a carbon layer can be provided on the surface of the silicon-carbon particles, which can further improve the rate performance and expansion inhibition performance of the secondary battery after being combined with the first substance.

[0050] In some embodiments, step S6 includes: transferring the silicon-carbon particles obtained in step S3 to a rotary kiln under nitrogen protection, introducing nitrogen for a period of time and then heating the temperature to 550°C at a rate of 10°C / min, and then continuously introducing acetylene gas. After keeping the temperature for 2 to 8 hours, the acetylene gas is cut off and the temperature is lowered. The obtained material is silicon-carbon particles with a carbon layer on the surface.

[0051] The present application also provides a secondary battery, comprising a positive electrode, a negative electrode and an electrolyte.

[0052] Secondary battery

[0053] The secondary battery of the present application is not particularly limited. According to the type of electron transport material, it is divided into various categories. For example, when the electron transport material is lithium (Li, including ions), the secondary battery is a lithium ion battery; when the electron transport material is sodium (Na, including ions), the secondary battery is a sodium ion battery.

[0054] According to one embodiment of the present application, a secondary battery may include a battery cell and an electrolyte. The battery cell may include a packaging material and an electrode assembly disposed inside the packaging material, and the electrolyte may be filled in an internal space formed by the packaging material. The packaging material may protect the electrode assembly from external impact and prevent the electrolyte from leaking to the outside. Depending on the shape of the packaging material, the battery cell may be divided into a prismatic, cylindrical, or soft-pack type.

[0055] The electrode assembly includes a positive electrode, a negative electrode and a separator, as well as other components known in the art in a secondary battery, which are not limited in this application. Among them, the separator can be between the positive electrode and the negative electrode.

[0056] The present application has no particular restrictions on the preparation method of the secondary battery, and for example, may include the following steps: stacking the positive electrode, the separator, and the negative electrode in order, and winding, folding, etc. them as needed to obtain an electrode assembly, placing the electrode assembly in a packaging material, injecting an electrolyte into the packaging material and sealing it to obtain a secondary battery.

[0057] positive electrode

[0058] In the present application, there is no special restriction on the positive electrode, as long as the purpose of the present application can be achieved. The positive electrode includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector; the above-mentioned "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be located on one surface of the positive electrode current collector along its own thickness direction, or on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the surface of the positive electrode current collector, or it can be a partial area of ​​the surface of the positive electrode current collector. There is no special restriction in the present application, as long as the purpose of the present application can be achieved.

[0059] The present application does not particularly limit the type, size and shape of the positive electrode current collector, as long as it does not cause chemical changes in the battery cell and has conductivity. For example, the positive electrode current collector can use materials such as stainless steel, aluminum, nickel, titanium, calcined carbon, or surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium or silver. In the present application, the positive electrode current collector may also contain non-metallic elements, such as non-metallic elements including at least one of fluorine, phosphorus, boron, chlorine, silicon, and sulfur.

[0060] The positive electrode current collector may have an appropriate thickness as required. Although not particularly limited, the positive electrode current collector may have a thickness in the range of 1 μm to 500 μm, or may have a thickness in the range of 1 μm to 300 μm, or may have a thickness in the range of 1 μm to 100 μm, or may have a thickness in the range of 1 μm to 50 μm, or may have a thickness in the range of 1 μm to 20 μm.

[0061] Unless otherwise specifically stated, the terms thickness (or height), width and length used in the present application refer to average values ​​and can be measured by measuring instruments that can measure thickness (or height), width and length, respectively, according to methods in the art.

[0062] The positive electrode current collector may form fine concavoconvexities on the surface, thereby further enhancing the adhesion with the positive electrode material layer. For example, the positive electrode current collector may be in the form of one or more selected from a film, a sheet, a foil, a net, a porous body, a foam and a non-woven fabric.

[0063] In the present application, the positive electrode material layer includes a positive electrode active material. The present application has no particular restrictions on the type of the positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include lithium nickel cobalt manganese oxide (LiNi 0.90 Co 0.05 Mn 0.05 O2(NCM 955 )、NCM 811 、NCM 622 、NCM 523 、NCM 111 ), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel lithium manganese oxide, spinel lithium nickel manganese oxide and lithium titanate. In the present application, the positive electrode active material may also contain non-metallic elements, for example, non-metallic elements include at least one of fluorine, phosphorus, boron, chlorine, silicon or sulfur. In the present application, there is no particular restriction on the thickness of the positive current collector and the positive electrode material layer, as long as the purpose of the present application can be achieved.

[0064] In some embodiments, the positive electrode material layer may further include a positive electrode binder. The present application does not particularly limit the type of positive electrode binder, as long as the purpose of the present application can be achieved. For example, the positive electrode binder may include but is not limited to polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified styrene-butadiene rubber (SBR), polyolefin ester, polyolefin alcohol, polyacrylic acid or polyurethane. In some embodiments, the polyolefin binder includes at least one of polyethylene or polypropylene.

[0065] In some embodiments, the positive electrode material layer may further include a conductive agent. The present application does not particularly limit the type of conductive agent in the positive electrode material layer, as long as the purpose of the present application can be achieved. In some exemplary embodiments, the conductive agent includes a carbon-based material, such as graphite such as natural graphite or artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, or carbon fiber; conductive polymers, such as polyphenylene derivatives; conductive metal oxides, such as zinc oxide, titanium oxide, etc.; conductive whiskers, such as potassium titanate, etc.; or a mixture formed by any combination of these substances.

[0066] In the present application, the positive electrode material layer can be formed by coating the positive electrode slurry on at least one side of the positive electrode current collector and drying it, and can be rolled after drying as needed. The positive electrode slurry contains the above-mentioned positive electrode active material, positive electrode binder and conductive agent. In addition, the positive electrode slurry may also contain a solvent. The present application does not particularly limit the type of solvent, as long as the purpose of the present application can be achieved. For example, the solvent can use N-methyl-2-pyrrolidone.

[0067] The present application has no particular restrictions on the mass ratios of the positive electrode active material, the conductive agent, and the positive electrode binder in the positive electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved. These mass ratios can apply known mass ratios.

[0068] negative electrode

[0069] The present application has no special restrictions on the negative electrode, as long as the purpose of the present application can be achieved. For example, the negative electrode includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. In the present application, the negative electrode material layer can be disposed on one surface in the thickness direction of the negative electrode current collector, or on two surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector, or it can be a partial area of ​​the negative electrode current collector. The present application has no special restrictions, as long as the purpose of the present application can be achieved.

[0070] The present application has no particular restrictions on the type, size and shape of the negative electrode current collector, as long as it does not cause chemical changes in the battery cell and has conductivity. For example, the negative electrode current collector may be made of, for example, stainless steel, copper, nickel, titanium, calcined carbon, or a material in which the surface of copper or stainless steel is surface-treated with carbon, nickel, titanium or silver.

[0071] The negative electrode current collector may have an appropriate thickness as required. Although not particularly limited, the negative electrode current collector may have a thickness in the range of 1 μm to 500 μm, or may have a thickness in the range of 1 μm to 300 μm, or may have a thickness in the range of 1 μm to 100 μm, or may have a thickness in the range of 1 μm to 50 μm, or may have a thickness in the range of 1 μm to 20 μm, or may have a thickness in the range of 5 μm to 10 μm.

[0072] The negative electrode current collector may have fine concavoconvexities on the surface, thereby further enhancing the adhesion with the negative electrode material layer. For example, the negative electrode current collector may be in the form of one or more selected from a film, a sheet, a foil, a net, a porous body, a foam and a non-woven fabric.

[0073] In some embodiments, the negative electrode material may also include other materials, such as, but not limited to, carbon materials such as graphite (artificial graphite, natural graphite or graphitized carbon fiber) or amorphous carbon; metals such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys that can be alloyed with lithium or alloys thereof with lithium; SiO β (0<β≤2), SnO, SnO2, vanadium oxide, lithium vanadium oxide and other metal oxides that can be doped or dedoped with lithium, or alloys formed with lithium; or Si-C composites or Sn-C composites and other composites containing the metal and carbon materials; or lithium titanate TiO2-Li4Ti5O 12 , and any one of them or a mixture of two or more thereof can be used. Specifically, the carbon material can use low crystalline carbon and high crystalline carbon, etc. Representative low crystalline carbons are soft carbon and hard carbon. Examples of high crystalline carbon can be amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, primary graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, carbon microspheres (mesophase carbon microspheres), mesophase pitch, and high temperature calcined carbons such as petroleum and coal-based coke (coke derived from petroleum or coal tar pitch), etc.

[0074] The negative electrode material layer in the present application also includes a negative electrode binder. The present application does not particularly limit the type of negative electrode binder, as long as the purpose of the present application can be achieved. For example, the negative electrode binder may include, but is not limited to, polyvinylidene fluoride (PVDF), polyvinyl alcohol, styrene butadiene rubber (SBR), polyethylene oxide, carboxymethyl cellulose (CMC), hydroxypropyl cellulose, cellulose acetate, diacetyl cellulose, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, polymethyl methacrylate, polybutyl acrylate, polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyarylate, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyurethane, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, styrene butadiene rubber, acrylic (ester) styrene butadiene rubber, epoxy resin or nylon. At least one of them.

[0075] The present application does not particularly limit the type of the conductive agent in the negative electrode material layer, as long as the purpose of the present application can be achieved. In some exemplary embodiments, the conductive agent includes carbon-based materials, such as graphite such as natural graphite or artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, or carbon fiber; metal-based materials, such as metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; conductive metal oxides, such as zinc oxide, titanium oxide, etc.; conductive whiskers, such as potassium titanate, etc.; or mixtures formed by any combination of these substances.

[0076] The present application has no particular restrictions on the mass ratios of the negative electrode material, negative electrode conductive agent, and negative electrode binder in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved. These mass ratios can apply known mass ratios.

[0077] In the present application, the negative electrode material layer can be formed by coating the negative electrode slurry on at least one side of the negative electrode current collector and drying it, and can be rolled after drying as needed. The negative electrode slurry contains the above-mentioned negative electrode material and negative electrode binder, and can further contain a conductive agent as needed. In addition, the negative electrode slurry can also contain a solvent, and the present application does not particularly limit the type of solvent, as long as the purpose of the present application can be achieved. For example, the solvent can use deionized water.

[0078] Diaphragm

[0079] The separator of the present application is used to prevent short circuit between the positive electrode and the negative electrode, and at the same time, it is a membrane that allows electron transport substances to pass through. The present application has no special restrictions on the separator, as long as it can achieve the purpose of the present application. For example, the material of the separator may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (such as polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, aramid, etc.; the type of the separator may include at least one of woven membranes, non-woven membranes, microporous membranes, composite membranes, rolled membranes, and spun membranes.

[0080] According to some embodiments of the present application, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, a film or a composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used.

[0081] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer with an inorganic substance. For example, the inorganic layer includes inorganic particles and a binder, and the present application has no particular restrictions on the inorganic particles, and may include, for example, at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The present application has no particular restrictions on the binder, and may, for example, be at least one of the above-mentioned positive electrode binder or negative electrode binder. The polymer layer contains a polymer, and the present application has no particular restrictions on the polymer, and for example, the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether or polyvinylidene fluoride and poly(vinylidene fluoride-hexafluoropropylene). In the present application, there is no particular limitation on the thickness of the separator, as long as the purpose of the present application can be achieved. For example, the thickness of the separator may be 5 μm to 500 μm.

[0082] Electrolyte

[0083] In the present application, the electrolyte refers to a medium that causes the movement of electron transport substances to smoothly carry out the electrochemical reactions of the positive and negative electrodes. The electrolyte can use commonly used organic liquid electrolytes, inorganic liquid electrolytes, gel-type polymer electrolytes, molten inorganic electrolytes, etc., but is not limited thereto. Solid electrolytes such as gel-type polymer electrolytes can also be used to replace the electrolyte. Batteries using solid electrolytes are generally referred to as solid-state batteries or all-solid-state batteries. The liquid electrolyte (electrolyte) generally contains a non-aqueous solvent and a lithium salt.

[0084] In some embodiments, the electrolyte includes at least one of ethyl acetate or ethyl fluoroacetate; based on the mass of the electrolyte, the mass proportion of ethyl acetate is E%, 1≤E≤20; preferably, 5≤E≤16; for example, E can be 1, 2, 3, 4, 6, 8, 9, 10, 13, 14, 15, 16, 18, 20 or a value in the range of any two thereof. Based on the mass of the electrolyte, the mass proportion of ethyl fluoroacetate is F%, 15≤F≤50; preferably, 20≤F≤30; illustratively, F can be 15, 16, 19, 22, 25, 28, 31, 33, 36, 37, 41, 42, 45, 47, 50 or a value in the range of any two thereof.

[0085] Based on the above scheme, the M element in the first substance can induce ethyl acetate and ethyl fluoroacetate to form a solid electrolyte interface film (SEI film) rich in inorganic substances on the surface of silicon-carbon particles, reduce the consumption of lithium ions in the electrolyte, and improve the compactness and stability of the SEI film, so as to buffer the volume expansion of silicon-carbon particles during the charging and discharging process, wherein ethyl fluoroacetate can further improve the flexibility of the SEI film and further adapt to the volume change of nano-silicon. The SEI film rich in Li element is also conducive to improving the interface compatibility between the negative electrode and the electrolyte, improving the wettability of the electrolyte to the above silicon-carbon particles, and promoting the transmission of lithium ions at the interface between the silicon-carbon particles and the electrolyte, thereby improving the expansion inhibition performance and rate performance of the secondary battery.

[0086] In some embodiments, the electrolyte includes a first lithium salt, and the first lithium salt is selected from at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, or lithium trifluoromethylsulfonate; based on the mass of the electrolyte, the mass proportion of the first lithium salt is S1%, 0.01≤S1≤1. Exemplarily, S1 can be 0.01, 0.07, 0.13, 0.24, 0.27, 0.32, 0.42, 0.49, 0.55, 0.66, 0.73, 0.83, 0.86, 0.92, 1, or a value in the range of any two thereof. The present application provides more free lithium ions through the first lithium salt, and the first substance in the surface area of ​​the silicon-carbon particles can further improve the ionic conductivity of the secondary battery system, while also being beneficial to improving the wettability of the electrolyte to the silicon-carbon particles, and forming a more stable LiF-rich SEI film on the surface of the silicon-carbon particles, buffering the volume expansion of the silicon-carbon particles, thereby further improving the expansion inhibition performance and rate performance of the secondary battery.

[0087] According to some embodiments of the present application, the lithium salt may also include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(oxalatoborate) {LiB(C2O4)2, LiBOB}, lithium difluorooxalatoborate {LiBF2(C2O4), LiDFOB}, LiNO3, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiC(SO2CF3)3, Li2SiF6 or lithium difluoroborate. The present application does not limit the content of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved.

[0088] The application has no particular restrictions on non-aqueous solvents. For example, non-aqueous solvents may include but are not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents. The above-mentioned carbonate compounds may include but are not limited to at least one of linear carbonate compounds, cyclic carbonate compounds or fluorocarbonate compounds. The above-mentioned linear carbonate compounds may include but are not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate or ethyl methyl carbonate (EMC). The above-mentioned cyclic carbonate may include but are not limited to at least one of propylene carbonate (PC), butylene carbonate or vinyl ethylene carbonate. The fluorinated carbonate compound may include, but is not limited to, at least one of 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The carboxylate compound may include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decalactone, valerolactone, or caprolactone. The above-mentioned ether compound may include but is not limited to at least one of 1,3-dioxolane (DOL), ethylene glycol dimethyl ether (1,2-dimethoxyethane, DME), dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran.

[0089] Electronic Devices

[0090] The present application further provides an electronic device, comprising the aforementioned secondary battery. Based on the aforementioned secondary battery, the electronic device of the present application can adapt to the conditions of rapid charge and discharge, and achieve excellent service life and safety.

[0091] The electronic device of the present application is not particularly limited, and it can be used for any electronic device known in the prior art. For example, the electronic device can include but is not limited to a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0092] Measurement method

[0093] The present application can be measured by the following method, and the physical properties in the following examples and comparative examples are measured by the following method.

[0094] Pore ​​size distribution and pore volume test

[0095] The porous carbon was tested using a physical adsorption instrument (model: ipore 620). The process included: taking 0.15 g of porous carbon as a sample and placing it in a sample tube, first degassing it at 200°C for 6 hours, and then testing the adsorption amount of argon by the sample at different pressures to draw the isothermal adsorption curve of the sample, and then using BET fitting to calculate the specific surface area of ​​the sample, and using non-local density functional theory (NLDFT) fitting to calculate the pore volume and pore size distribution of the sample, and then calculating the pore volume ratio of type I pores and type II pores based on the pore volume.

[0096] M element and mass ratio test

[0097] The ICP method was used for element content analysis, and the ICP-OES (PE Avio 200) equipment was used to measure the mass proportion of the M element in the silicon-carbon particles.

[0098] Carbon layer thickness test

[0099] After obtaining a thin slice sample of silicon-carbon particles by FIB, the thickness of the coated carbon layer was measured using TEM. The thickness of the carbon layer was measured at 10 different positions such as the edge and the center, and the arithmetic mean was calculated as the thickness of the carbon layer.

[0100] Ionic conductivity test

[0101] The GITT method was used to test the ionic conductivity. The process included: 1) mixing silicon carbon particles: binder (polymethyl acrylate): conductive agent (carbon nanotubes) in a ratio of 8:1:1 to make a slurry, then coating, drying, cold pressing, punching and assembling into a pair of lithium half-cells; 2) subjecting the half-cell to the first cycle at a rate of 0.1C, with a voltage range of 0.005V to 2.0V; 3) discharging the half-cell at a constant current of 0.1C to 0.005V, then discharging at a constant current of 0.1C for 10min, standing for 1h, and repeating the above steps until the buckling voltage is ≤0.005V; 4) extracting the steady-state voltage and using the following formula to calculate the ionic conductivity (ion diffusion coefficient) D:

[0102]

[0103] Cyclic expansion performance test

[0104] The lithium-ion full battery was placed in a constant temperature box at 25℃±1℃ for 30 minutes, charged to 4.35V at 0.5C constant current, then charged to 0.025C at 4.35V constant voltage, placed for 5 minutes, and then discharged to 3.0V at 0.5C. This is a charge and discharge cycle process. The initial thickness H0 of the lithium-ion full battery was recorded. After that, the above cycle process was repeated for 600 cycles. The thickness H1 after the 600th cycle was recorded.

[0105] Cycle expansion ratio = H0 / H1×100%.

[0106] Rate performance test

[0107] The lithium-ion full battery was left standing at a test temperature of 25°C for 5 minutes, then charged to 4.35V at a constant current of 0.5C, and then charged to 0.025C at a constant voltage of 4.35V; left standing for 5 minutes, and then discharged to 3.0V at a constant current of 0.2C, and the 0.2C discharge capacity was recorded; then left standing for 5 minutes, the above charging process was repeated, and then the battery was discharged at a constant current of 2C, and the 2C discharge capacity was recorded.

[0108] Rate capacity retention rate = 2C discharge capacity / 0.2C discharge capacity × 100%.

[0109] The following uses lithium-ion batteries as an example to illustrate the solution of the present application in combination with the following specific embodiments. Unless otherwise specified, the raw materials used in the following embodiments are all from common commercial products, and the devices or equipment used are all purchased from conventional market sales channels.

[0110] Example 1-1

[0111] Preparation method of silicon carbon particles:

[0112] Step S1, carbonizing phenolic resin as a precursor material at 900° C. for 2 h in a nitrogen atmosphere to obtain a carbonized material.

[0113] Step S2, then placing the carbonized material in a reaction furnace, heating it to 860° C., then introducing water vapor to form pores, and keeping the temperature for 14 hours to obtain the first activated material.

[0114] Step S3, then heating the first activated material to 1100° C. in a nitrogen atmosphere, introducing water vapor, and keeping the temperature for 5 hours to obtain porous carbon.

[0115] Step S4, take the porous carbon and place it in a fluidized bed equipment, introduce nitrogen into the inside to make it completely fluidized, and then increase the temperature to 500°C at a heating rate of 5°C / min; after the temperature in the fluidized bed stabilizes, introduce silane gas, keep it warm for 3 hours, obtain silicon precipitate particles, then switch to nitrogen and gradually cool to room temperature.

[0116] Step S5, transfer the silicon precipitate particles to anhydrous acetonitrile under nitrogen protection, add Li2S and P2S5 in a molar ratio of 7:3, stir evenly, and heat in a vacuum environment to evaporate the solvent to obtain silicon-carbon particles.

[0117] Preparation of negative electrode:

[0118] Silicon-carbon particles and artificial graphite are mixed in a mass ratio of 10:90 to obtain negative electrode active materials. The negative electrode active material (95wt%), carbon nanotubes (0.5wt%), polymethyl acrylate (3.5%), and sodium carboxymethyl cellulose (1%) are mixed, and then deionized water is added and stirred evenly to prepare a negative electrode slurry. The negative electrode slurry is evenly coated on one surface of the copper foil, and after drying, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet coated with a negative electrode material layer on both sides. The coated copper foil is dried, pressurized, and cut into a specified size, and the pole ears are welded to make a negative electrode.

[0119] Preparation of positive electrode:

[0120] Lithium cobalt oxide (97 wt%), conductive carbon black (1.5 wt%), and polyvinylidene fluoride (1.5 wt%) were mixed in N-methylpyrrolidone to prepare positive electrode slurry. The positive electrode slurry was evenly coated on one surface of the aluminum foil, and the coating step was repeated on the other surface of the aluminum foil after drying to obtain a positive electrode sheet with a double-sided positive electrode material layer. The coated aluminum foil was dried, pressurized, and cut into a specified size, and the tabs were welded to make the positive electrode.

[0121] Preparation of diaphragm: A 12 μm thick polyethylene (PE) microporous membrane was selected as the diaphragm.

[0122] Preparation of electrolyte:

[0123] In an argon atmosphere glove box with a water content of less than 10ppm, ethylene carbonate (EC) and diethyl carbonate (DEC) (mass ratio 1:1) were mixed to obtain a base solvent, and then ethyl fluoroacetate and lithium hexafluorophosphate were added to the base solvent and mixed evenly to obtain an electrolyte. Based on the mass of the electrolyte, the mass content of lithium hexafluorophosphate was 12.5%, the mass content of ethyl fluoroacetate was 20%, and the remainder was the base solvent.

[0124] Lithium-ion full battery production:

[0125] The positive electrode, separator and negative electrode are stacked in order, so that the separator is placed between the positive electrode and the negative electrode to play an isolating role, and the electrode assembly is wound, and the electrode assembly is placed in an outer packaging aluminum-plastic film, and the above-mentioned electrolyte is injected after baking. After vacuum packaging, standing, formation, shaping, capacity testing and other processes, a lithium-ion full battery is obtained.

[0126] Example 1-2 to Example 1-21, Comparative Example 1-1 to Comparative Example 1-5

[0127] The only difference from Example 1-1 is that the mass percentage C% of the M element, the pore volume percentage P% of the second type of pores and the thickness of the carbon layer are adjusted according to Table 1. The specific adjustment parameters and performance test results are shown in Table 1 below. Among them, in each embodiment or comparative example in Table 1, the pore area percentage of the surface area is greater than the pore area percentage of the internal area through the second activation of step S3, and the mass percentage C% of the M element is increased by increasing the amount of M source added; the reaction temperature in step S3 is increased, the reaction time is extended, and the pore volume percentage P% of the second type of pores in the porous carbon is increased; the porous carbon of comparative example 1-1 is not subjected to the secondary activation of step S3, and the surface area and the internal pore size distribution are the same, that is, the pore volume percentage of the larger pore size pores in the surface area is small, so the M element bound to the surface area is also small.

[0128] The silicon-carbon particle flake samples of Example 1-1 and Comparative Example 1-1 were prepared by focused ion beam (FIB), and the flake samples were observed by transmission electron microscope (TEM). By comparing the pore area of ​​the surface region and the pore area of ​​the internal region, it can be seen that the pore area of ​​the surface region of the silicon-carbon particle flake sample of Example 1-1 is larger than the pore area of ​​the internal region, and the pore area of ​​the surface region of the silicon-carbon particle flake sample of Comparative Example 1-1 is smaller than the pore area of ​​the internal region.

[0129] The pore size distribution curve of the porous carbon of Example 1-1 was tested by a physical adsorption instrument. Figure 1 As shown, it can be seen that the porous carbon includes type I pores and type II pores. The pore diameter of type I pores is D1 nm, 0.5≤D1<2, and the pore diameter of type II pores is D2 nm, 2≤D1≤15. Based on the sum of the pore volume of type I pores and the pore volume of type II pores, the pore volume of type II pores accounts for P%=9%.

[0130] The method for preparing silicon-carbon particles of Examples 1-16 to 1-21 further includes: step S6, transferring the silicon-carbon particles to a rotary kiln under nitrogen protection, introducing nitrogen for a period of time, raising the temperature to 550°C at a rate of 10°C / min, and then continuously introducing acetylene gas, keeping the temperature for a period of time, cutting off the acetylene gas and cooling the temperature to obtain silicon-carbon particles with a carbon layer on the surface. The thickness T nm of the carbon layer is increased by increasing the insulation time in step S6.

[0131] Table 1

[0132]

[0133]

[0134] As can be seen from Table 1, the present application controls the pore area of ​​the surface area in the cross section of the silicon-carbon particles to be larger than the pore area of ​​the internal area, and in combination with the first substance containing the M element, the secondary battery can exhibit excellent rate performance and expansion suppression performance. In particular, when the mass proportion C% of the M element in the silicon-carbon particles is further controlled to meet 0.3≤C≤6, the secondary battery can exhibit more excellent rate performance and expansion suppression performance. In particular, when it meets 0.6≤C≤4, the expansion suppression performance and rate performance of the secondary battery can be further improved.

[0135] In particular, in the porous carbon of the silicon-carbon particles, the pore volume of the second type of pores, based on the sum of the pore volume of the first type of pores and the pore volume of the second type of pores, the pore volume proportion P% satisfies 2≤P≤20, which can further improve the expansion suppression performance and rate performance of the secondary battery. In particular, when 4≤P≤15 is satisfied, the rate performance and expansion suppression performance of the secondary battery can be further improved.

[0136] In particular, when a carbon layer is further provided on the surface of the silicon-carbon particles, and the thickness T nm of the carbon layer is adjusted to satisfy 5≤T≤80, the rate performance and expansion suppression performance of the secondary battery can be further improved. In particular, when 10≤T≤50 is satisfied, the rate performance and expansion suppression performance of the secondary battery can be further improved. In particular, when 20≤C×T≤60 is satisfied, the mutual coordination effect of the carbon layer and the first substance can be enhanced, and the rate performance and expansion suppression performance of the secondary battery can be further improved.

[0137] Example 2-1 to Example 2-13

[0138] The only difference compared with Example 1-19 is that the types and mass proportions of ethyl acetate, ethyl fluoroacetate and the first lithium salt in the electrolyte are adjusted according to Table 2, and the specific adjustment parameters and performance test results are shown in Table 2. At the same time, the content of the basic solvent is adaptively adjusted, wherein the mass ratio of EC and DEC remains unchanged.

[0139] Table 2

[0140]

[0141]

[0142] As can be seen from Table 2, regulating the mass proportion F% of ethyl fluoroacetate in the electrolyte to meet 15≤F≤50 is conducive to improving the expansion inhibition performance and rate performance of the secondary battery, especially when 20≤F≤30 is met, the expansion inhibition performance and rate performance of the secondary battery can be further improved. In particular, when ethyl acetate is further added to the electrolyte and its mass proportion E% is adjusted to meet 1≤E≤20, the expansion inhibition performance and rate performance of the secondary battery can be further improved. In particular, when 5≤E≤16 is met, the expansion inhibition performance and rate performance of the secondary battery can be further improved.

[0143] In particular, adding the first lithium salt to the electrolyte and adjusting its mass percentage S1% to satisfy 0.01≤S1≤1 can further improve the expansion suppression performance and rate performance of the secondary battery.

[0144] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the principles of the present application should be included in the protection scope of the present application.

Claims

1. A negative electrode material, characterized in that: The negative electrode material includes silicon-carbon particles, the cross section of the silicon-carbon particles includes a surface area and an internal area, the surface area contains a first substance, and the first substance has ion conductivity; the first substance contains an M element, and the M element is selected from at least one of an S element, an N element, an La element, an Ti element, an Zr element, an Al element, an P element, and a Cl element; The pore area ratio of the surface region is greater than the pore area ratio of the internal region; The surface region refers to a region between 0 nm and 500 nm away from the surface of the silicon-carbon particles, and the internal region refers to a region between 600 nm and 1200 nm away from the surface of the silicon-carbon particles.

2. The negative electrode material according to claim 1, characterized in that The silicon-carbon particles contain porous carbon, which includes type I pores and type II pores. The pore diameter of the type I pores is D1 nm, 0.5≤D1<2, and the pore diameter of the type II pores is D2 nm, 2≤D1≤15. Based on the sum of the pore volume of the type I pores and the pore volume of the type II pores, the pore volume proportion of the type II pores is P%, 2≤P≤20.

3. The negative electrode material according to claim 2, characterized in that 4≤P≤15。 4. The negative electrode material according to any one of claims 1 to 3, characterized in that The first substance is selected from lithium aluminum oxide, lithium phosphate, Li x1 PO y1 N z1 , where 2.8≤x1≤3.3, 3.0≤y1≤3.8, 0.16≤z1≤0.46, Li7La3Zr2O 12 , Li 3x2 La 2 / 3-x2 TiO3, where 0.06≤x2≤0.16, lithium thiophosphate, Li 1+x3 Al x3 Ti 2-x3 (PO4)3, wherein 0≤x3≤0.7, at least one of Li6PS5Cl.

5. The negative electrode material according to any one of claims 1 to 3, characterized in that Based on the mass of the silicon-carbon particles, the mass proportion of the M element is C%, 0.3≤C≤6; preferably, 0.6≤C≤4.

6. The negative electrode material according to claim 5, characterized in that The silicon-carbon particles contain porous carbon and nano-silicon located in the pores of the porous carbon; a carbon layer is arranged on the surface of the silicon-carbon particles, and the thickness of the carbon layer is T nm, 5≤T≤80; preferably, 10≤T≤50.

7. The negative electrode material according to claim 6, characterized in that 20≤C×T≤60.

8. The method for preparing a negative electrode material according to any one of claims 1 to 7, characterized in that: At least the following steps are included: Step S1, calcining the precursor material at T1°C in an inert gas atmosphere for t1 hours to obtain a carbonized material; 550≤T1≤1600, 2≤t1≤10; Step S2, after the carbonized material is crushed, a first activated gas is introduced at T2°C and reacted for t2 hours to obtain a first activated material; 780≤T2≤950, 8≤t2≤20; the first activated gas is at least one of water vapor and carbon dioxide; Step S3, heating the first activated material to T3°C in an inert gas atmosphere, introducing a second activated gas, and reacting for t3 hours to obtain porous carbon; 850≤T3≤1300, 2≤t3≤8; the second activated gas is at least one of water vapor, carbon dioxide or oxygen; Step S4, introducing silane gas into the porous carbon at T4°C and keeping the temperature for t4 hours to obtain silicon-precipitated particles; 380≤T4≤600, 2≤t4≤5; Step S5, transferring the silicon-precipitated particles to a dispersion medium in an inert gas protection atmosphere, adding an M element source and dispersing the particles, and then evaporating the dispersion medium in a vacuum environment to obtain the silicon-carbon particles.

9. The preparation method according to claim 8, characterized in that: The preparation method further comprises: Step S6, heating the silicon-carbon particles to T5°C in an inert gas protection atmosphere, introducing acetylene gas, and keeping the temperature for t5 hours; 500≤T5≤700, 2≤t5≤8.

10. A secondary battery, characterized in that: It includes a positive electrode, a negative electrode and an electrolyte; the negative electrode includes a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector; The negative electrode material layer comprises the negative electrode material according to any one of claims 1 to 7 or the negative electrode material prepared by the preparation method according to claim 8 or 9.

11. The secondary battery according to claim 10, characterized in that: The electrolyte includes at least one of ethyl acetate or ethyl fluoroacetate; Based on the quality of the electrolyte, the electrolyte satisfies at least one of the following conditions: (1) The mass proportion of ethyl acetate is E%, 1≤E≤20; preferably, 5≤E≤16; (2) The mass proportion of the ethyl fluoroacetate is F%, 15≤F≤50; preferably, 20≤F≤30.

12. The secondary battery according to claim 10, characterized in that: The electrolyte includes a first lithium salt, the first lithium salt being selected from at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide or lithium trifluoromethylsulfonate; Based on the mass of the electrolyte, the mass proportion of the first lithium salt is S1%, 0.01≤S1≤1.

13. An electronic device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 10 to 12.

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