Porous carbon material and preparation method thereof, silicon carbon material and application

Abstract

The invention discloses a porous carbon material and a preparation method thereof, a silicon carbon material and application. The porous carbon material comprises first-class pores, second-class pores and third-class pores, the aperture of the first-class hole is P1nm, and P1 is more than 0 and less than or equal to 1; the aperture of the second-class holes is P2nm, and P2 is more than 1 and less than or equal to 3; the aperture of the three types of holes is P3nm, and P3 is more than 3 and less than or equal to 10; based on the sum of the pore volumes of the first-class pores, the second-class pores and the third-class pores, the volume ratio of the first-class pores is V1%, the volume ratio of the second-class pores is V2%, and the volume ratio of the third-class pores is V3%; 0.1 < = V1 < = 10, 50 < = V2 < = 95. The silicon-carbon material is prepared from the porous carbon material with the graded pore diameters, so that the first coulombic efficiency of the silicon-carbon material can be improved, and the high-temperature performance and the safety performance of the secondary battery are improved at the same time.

Description

Technical Field

[0001] The present application belongs to the technical field of battery materials, and specifically relates to a porous carbon material and a preparation method thereof, a silicon-carbon material and applications thereof. Background Art

[0002] Secondary batteries, such as lithium-ion batteries, are battery systems that can be repeatedly charged and discharged. During the charge and discharge process, lithium ions are embedded and deintercalated back and forth between the positive and negative electrodes to achieve the storage and release of electrical energy. As an important component of the battery, the negative electrode material has a crucial impact on the performance of the battery. Common negative electrode materials include graphite, silicon materials, etc. Among them, silicon materials have attracted much attention due to their high specific capacity, but their volume expansion problem during the charge and discharge process has always been a key factor restricting their application.

[0003] During the cycle, the volume change rate of silicon is as high as 300%, especially under high temperature conditions, it is even higher. This drastic volume expansion will generate great stress inside the battery, causing changes in the physical structure of the electrode material, such as cracks, powderization, etc., causing the active material to detach from the pole piece, thereby destroying the contact between the electrode material and the current collector, causing the battery capacity to decay rapidly. And the expansion may also cause the reduction of the internal porosity of the battery, reduce the lithium ion movement channel, cause the precipitation of lithium metal, and affect the safety of the battery. In addition, when external extrusion is applied to silicon system batteries, the negative impact of this volume change will be further amplified. Specifically, external extrusion will increase the mechanical stress inside the battery, making the silicon material more prone to cracks and powderization, and may also damage key components such as the diaphragm, causing internal short circuits, and posing serious safety risks. Therefore, it is necessary to improve the high temperature expansion problem and extrusion safety performance of secondary batteries to improve the cycle stability and safety of secondary batteries. Summary of the invention

[0004] In view of this, the present application provides a porous carbon material and a preparation method thereof, a silicon-carbon material and an application thereof. By adopting a porous carbon material with graded pore sizes to prepare a silicon-carbon material, the first coulombic efficiency of the silicon-carbon material can be improved, while also improving the high-temperature expansion suppression performance and extrusion safety performance of the secondary battery.

[0005] In a first aspect, the present application provides a porous carbon material, comprising a first type of pore, a second type of pore and a third type of pore; the pore size of the first type of pore is P 1 nm,0<P 1 ≤1; the aperture of the second type of hole is P 2 nm,1<P 2 ≤3; the aperture of the three types of holes is P 3 nm,3<P 3 ≤10; Based on the sum of the pore volumes of type I, type II, and type III pores, the volume proportion of type I pores is V 1%, and the volume proportion of the second type of pores is V 2 %, and the volume proportion of the three types of pores is V 3 %;0.1≤V 1 ≤10,50≤V 2 ≤95. The present application satisfies the above characteristics by controlling the hierarchical pore structure of the porous carbon material, wherein the first type of pores can increase the density and compression strength of the porous carbon material; the second type of pores can provide abundant active sites for depositing silicon materials, so that the silicon material is deposited in the second type of pores as much as possible. On the one hand, the grain size of the silicon material can be limited, and the volume expansion amplitude of the silicon material during the process of embedding and removing lithium can be reduced. On the other hand, the combination of the second type of pores and the first type of pores can give the porous carbon material good mechanical flexibility and structural stability, improve the carbon wall strength of the porous carbon material, and provide a buffer space for the volume expansion of the silicon material, thereby absorbing and dispersing the internal stress generated by the volume change of the silicon material under high temperature cycle conditions, as well as the stress from the outside under extrusion conditions, which helps to maintain the structural integrity of the silicon-carbon material and the electrode assembly. In addition, the combination of the first type of pores, the second type of pores and the third type of pores can also absorb and disperse heat, reduce or avoid thermal runaway caused by local overheating, and also help the rapid transmission of lithium ions, improve the conductivity of lithium ions, reduce the possibility of lithium metal precipitation, and reduce the heat accumulation caused by the obstruction of lithium ion transmission. Therefore, the present application defines the porous carbon material as including a pore size grading structure of type I pores, type II pores and type III pores, and regulates the pore volume ratio of type I pores and type II pores to conform to the above range, which can improve the first coulombic efficiency of the silicon-carbon material and its electrochemical performance under high temperature or extrusion conditions, thereby improving the secondary battery's high temperature expansion inhibition performance and extrusion safety performance.

[0006] In some embodiments, the porous carbon material satisfies at least one of the following conditions:

[0007] (1) 0.5 ≤ V 1 ≤10;

[0008] (2)50≤V 2 ≤85;

[0009] (3)5≤V 3 ≤45;

[0010] (4)0.1≤V 1 / V 3 ≤20.

[0011] Based on the above scheme, the coordination effect of type I pores, type II pores and type III pores can be improved, the internal stress caused by the volume change of silicon materials under high-temperature cycling conditions and the stress from the outside under extrusion conditions can be absorbed and dispersed, the pulverization and breakage of silicon-carbon materials can be reduced, and the conductivity of lithium ions can be improved, thereby further improving the first coulomb efficiency of silicon-carbon materials, as well as the high-temperature expansion inhibition performance and extrusion safety performance of secondary batteries.

[0012] In some embodiments, the pore volume of the porous carbon material is 0.50 cm 3 / g to 1.0cm 3 / g; and / or, the elastic modulus of the porous carbon material is 1GPa to 50GPa, preferably 23GPa to 44GPa. On the basis of the above-mentioned pore size classification structure, the pore volume and / or elastic modulus of the porous carbon material are regulated to meet the above-mentioned range, so that it has a suitable silicon deposition amount, balances the energy density and buffer space of the silicon-carbon material, is conducive to absorbing and dispersing stress and heat, improves the conductivity of lithium ions, and further improves the first coulomb efficiency of the silicon-carbon material, as well as the high-temperature expansion inhibition performance and extrusion safety performance of the secondary battery.

[0013] The present application also provides a method for preparing the aforementioned porous carbon material, comprising the following steps:

[0014] Step S1, carbonizing a carbon precursor in an inert gas atmosphere to obtain a carbonized material;

[0015] Step S2, mixing the carbonized material and the pore-forming agent in a mass ratio of 1: (0.2-2.5) to obtain a mixture; then activating the mixture in an inert gas atmosphere to obtain an activated material; the activation treatment includes sequentially performing an activation treatment at T 1 Keep warm at t 1 Hours, T 2 Keep warm at t 2 Hours and T 3 Keep warm at t 3 Hours; among which, 700≤T 1 ≤800,0.1≤t 1 ≤1;800<T 2 ≤900,4≤t 2 ≤7;900<T 3 ≤1000,0.5≤t 3 ≤4;

[0016] Step S3, washing the activated material with water and acid solution in turn, and filtering to obtain a porous carbon material.

[0017] Based on the above scheme, the present application adopts a gradient insulation design during the activation treatment process, and utilizes the different reaction rates of the pore former and the carbonized material at different temperatures. By controlling the insulation time and temperature at different stages, it is possible to regulate the proportion and distribution of type I pores, type II pores and type III pores in the porous carbon material, thereby realizing the preparation of porous carbon materials with graded pore sizes, and further improving the first coulombic efficiency of silicon-carbon materials, as well as the high-temperature expansion inhibition performance and extrusion safety performance of secondary batteries.

[0018] The present application also provides a silicon-carbon material, including a porous carbon material and a silicon material located in the pores of the porous carbon material; the porous carbon material includes any of the aforementioned porous carbon materials or the porous carbon material obtained by the aforementioned preparation method; the grain size of the silicon material is 0.9nm to 2nm. The present application can limit the grain size of the silicon material and alleviate its volume expansion through the above-mentioned graded aperture structure, which is also beneficial to improve the utilization rate of the silicon material in the electrochemical reaction and improve the first coulomb efficiency of the silicon-carbon material; and the above-mentioned graded aperture structure can also absorb and disperse stress and heat through the buffer space remaining after the deposition of the silicon material, enhance the structural stability of the silicon-carbon material, and improve the high-temperature expansion suppression performance and extrusion safety performance of the secondary battery.

[0019] 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 current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector; the negative electrode material layer comprises the aforementioned silicon-carbon material; the compaction density of the negative electrode material layer is 0.95 g / cm 3 Up to 1.05g / cm 3 When the compaction density of the negative electrode material layer is further adjusted within the above range, the energy density and internal buffer space of the secondary battery can be balanced, the wettability and contact efficiency of the silicon-carbon particles and the electrolyte can be improved, the internal expansion stress and external extrusion stress can be dispersed, and the material breakage and lithium metal precipitation can be reduced, thereby further improving the first coulomb efficiency of the silicon-carbon material, as well as the high-temperature expansion inhibition performance and extrusion safety performance of the secondary battery.

[0020] In some embodiments, the electrolyte includes propylene carbonate and ethylene carbonate, and the sum of the mass proportions of propylene carbonate and ethylene carbonate is E%, 10≤E≤30 based on the mass of the electrolyte. Propylene carbonate and ethylene carbonate can promote the formation of a stable solid electrolyte interface film (SEI film), and the higher viscosity of the two is beneficial to improve the anti-extrusion ability of the battery, but the wettability of the electrolyte will be lost. The hierarchical pore size structure of the porous carbon material of the present application can provide a suitable buffer space for the silicon material. By controlling the sum of the mass proportions of propylene carbonate and ethylene carbonate in the electrolyte to meet the above conditions, the viscosity of the electrolyte and the film-forming effect can be balanced. The above buffer space can also increase the diffusion path of lithium ions, and is conducive to promoting the formation of a more uniform, more stable and thinner SEI film on the surface of the silicon-carbon material, which can reduce the consumption of lithium ions in the electrolyte, and reduce the side reactions of the silicon-carbon material and the electrolyte, which helps to further improve the first coulomb efficiency, and improve the high-temperature expansion inhibition and extrusion safety performance of the secondary battery.

[0021] In some embodiments, the electrolyte includes lithium tetrafluoroborate, and the mass proportion of lithium tetrafluoroborate is S1%, 0.01≤S1≤0.8, and preferably 0.05≤S1≤0.6 based on the mass of the electrolyte. The present application uses lithium tetrafluoroborate in the electrolyte. When the mass proportion is within the above range, it can add boron-containing and fluorine-containing components to the SEI film on the surface of the silicon-carbon material, and cooperate with ethylene carbonate and propylene carbonate to improve the flexibility and density of the SEI film, reduce the breakage of the SEI film and the side reaction of the electrolyte, and further enhance the structural stability of the silicon-carbon material of the present application. In addition, by utilizing its higher ionic conductivity and the buffer space inside the silicon-carbon material, the transmission rate of lithium ions can be further improved, and the precipitation of lithium metal can be reduced or avoided, so that the first coulomb efficiency of the secondary battery, the high-temperature expansion performance and the extrusion safety performance can be further improved.

[0022] In some embodiments, the electrolyte includes lithium bis(trifluoromethylsulfonyl imide), and the mass proportion of lithium bis(trifluoromethylsulfonyl imide is S2% based on the mass of the electrolyte, 0.05≤S2≤2, preferably 0.1≤S2≤1.2. The present application regulates the mass proportion of lithium bis(trifluoromethylsulfonyl imide) in the electrolyte to meet the above range, and the combination with lithium tetrafluoroborate can further increase the content of inorganic substances such as LiF in the SEI film, improve the density, stability and ion conductivity of the SEI film, thereby enhancing the SEI film's ability to transport lithium ions and its protective effect on silicon-carbon materials, and further improving the first coulomb efficiency of the secondary battery, the high-temperature expansion inhibition performance and the extrusion safety performance.

[0023] In addition, the present application also relates to an electronic device, comprising the aforementioned secondary battery. DETAILED DESCRIPTION

[0024] 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.

[0025] In order to solve the problems in the prior art, the present application provides a porous carbon material, including type I pores, type II pores and type III pores; the pore size of type I pores is P 1 nm,0<P 1 ≤1; the aperture of the second type of hole is P 2 nm,1<P 2 ≤3; the aperture of the three types of holes is P 3 nm,3<P 3 ≤10; Based on the sum of the pore volumes of type I, type II, and type III pores, the volume proportion of type I pores is V 1 %, and the volume proportion of the second type of pores is V 2 %, and the volume proportion of the three types of pores is V 3 %;0.1≤V 1 ≤10,50≤V 2 ≤95.

[0026] The inventors found that: the present application satisfies the above characteristics by controlling the hierarchical pore structure of the porous carbon material, wherein the first type of pores can increase the density and compression strength of the porous carbon material; the second type of pores can provide abundant active sites for depositing silicon materials, so that the silicon materials are deposited in the second type of pores as much as possible, which can limit the grain size of the silicon material and reduce the volume expansion amplitude of the silicon material during the process of embedding and removing lithium. On the other hand, the second type of pores and the first type of pores can give the porous carbon material good mechanical flexibility and structural stability, improve the carbon wall strength of the porous carbon material, and provide a buffer space for the volume expansion of the silicon material, thereby absorbing and dispersing the internal stress generated by the volume change of the silicon material under high temperature cycle conditions, and the stress from the outside under extrusion conditions, which helps to maintain the structural integrity of the silicon-carbon material and the electrode assembly. In addition, the combination of the first type of pores, the second type of pores and the third type of pores can also absorb and disperse heat, reduce or avoid thermal runaway caused by local overheating, and also help the rapid transmission of lithium ions, improve the conductivity of lithium ions, reduce the precipitation of lithium metal, and reduce the heat accumulation caused by the obstruction of lithium ion transmission. Therefore, the present application defines the porous carbon material as including a pore size grading structure of type I pores, type II pores and type III pores, and regulates the pore volume ratio of type I pores and type II pores to conform to the above range, which can improve the first coulombic efficiency of the silicon-carbon material and its electrochemical performance under high temperature or extrusion conditions, thereby improving the secondary battery's high temperature expansion inhibition performance and extrusion safety performance.

[0027] In some embodiments, 0.1≤V 1 ≤10, preferably 0.5≤V 1≤10; illustratively, V 1 The value can be 0.1, 0.4, 2.0, 3.2, 3.5, 5.1, 6.1, 7.4, 8.8, 9.5, 10 or a value within the range formed by any two of them. The present application controls the volume proportion of a type of pores to meet the above range, which can increase the density and compression strength of the porous carbon material, improve the carbon wall strength of the porous carbon material, help maintain the structural integrity of the silicon-carbon material and the electrode assembly under the conditions of silicon material volume expansion and external extrusion, improve the first coulomb efficiency of the silicon-carbon material, and the high-temperature expansion inhibition performance and extrusion safety performance of the secondary battery.

[0028] In some embodiments, 50 ≤ V 2 ≤95, preferably 50≤V 2 ≤85; illustratively, V 2 The value can be 50, 51, 58, 63, 68, 70, 78, 83, 86, 93, 95 or a value within the range formed by any two of them. The present application regulates the volume proportion of the second type of pores in the porous carbon material to meet the above range, which can limit the grain size of the silicon material, reduce the volume expansion amplitude of the silicon material during the process of embedding and extracting lithium, and promote the improvement of the mechanical flexibility and structural stability of the porous carbon material, absorb and disperse stress and heat, improve the first coulomb efficiency of the silicon-carbon material, and the high-temperature expansion inhibition performance and extrusion safety performance of the secondary battery.

[0029] In some embodiments, 5 ≤ V 3 ≤45; illustratively, V 3 The value is within the range of 5, 9, 10, 17, 22, 25, 27, 35, 36, 42, 45 or any two thereof. The present application regulates the volume proportion of the three types of pores in the porous carbon material to meet the above range, which can provide a suitable buffer space to absorb and disperse stress from the inside and / or outside, and also contribute to the penetration of the electrolyte and the rapid transmission of lithium ions, improve the conductivity of lithium ions, reduce or avoid the precipitation of lithium metal, thereby maintaining the structural integrity of the silicon-carbon material and the electrode assembly when the silicon material expands and is squeezed by the outside world, and can also reduce heat accumulation, reduce or avoid thermal runaway caused by local overheating, and thus improve the first coulomb efficiency of the silicon-carbon material, as well as the high-temperature expansion inhibition performance and extrusion safety performance of the secondary battery.

[0030] In some embodiments, 0.1≤V 1 / V 3 ≤20. For example, V 1 / V 3The value is within the range of 0.1, 2.1, 3.3, 4.6, 7.3, 9.2, 11.9, 14.4, 17.5, 18.5, 20 or any two thereof. When the volume ratio of the first type of pores and the third type of pores meets the above range, the coordination effect of the first type of pores, the second type of pores and the third type of pores can be comprehensively improved, the stress from the inside and / or the outside can be absorbed and dispersed, the pulverization and crushing of the silicon-carbon material can be reduced, and the conductivity of lithium ions can be improved, thereby further improving the first coulomb efficiency of the silicon-carbon material, as well as the high temperature expansion inhibition performance and extrusion safety performance of the secondary battery.

[0031] In some embodiments, the pore volume of the porous carbon material is 0.50 cm 3 / g to 1.0cm 3 / g; for example, the pore volume of a porous carbon material is 0.5 cm 3 / g, 0.54cm 3 / g, 0.60cm 3 / g, 0.61cm 3 / g, 0.72cm 3 / g, 0.74cm 3 / g, 0.78cm 3 / g, 0.85cm 3 / g, 0.90cm 3 / g, 0.96cm 3 / g, 1cm 3 / g or a value within the range of any two thereof. When the pore volume of the porous carbon material is regulated within the above range, it is beneficial to provide a suitable buffer space, absorb and disperse stress from the inside and / or outside, promote full contact between the silicon-carbon material and the electrolyte, and improve the electrochemical reaction activity. In combination with the above pore size distribution, it is possible to improve the utilization rate of the pores while maintaining a certain specific surface area, so that the silicon-carbon material exhibits better performance in the battery, further improve the first coulomb efficiency of the silicon-carbon material, and the high-temperature expansion inhibition performance and extrusion safety performance of the secondary battery.

[0032] In some embodiments, the elastic modulus of the porous carbon material is 1 GPa to 50 GPa, preferably 23 GPa to 44 GPa. Exemplarily, the elastic modulus of the porous carbon material is 1 GPa, 3 GPa, 8 GPa, 14 GPa, 18 GPa, 26 GPa, 31 GPa, 38 GPa, 40 GPa, 45 GPa, 50 GPa or a value within the range composed of any two of them. On the basis of the above-mentioned pore size classification structure, the elastic modulus of the porous carbon material is regulated to conform to the above-mentioned range, which can improve the mechanical flexibility and structural stability of the porous carbon material, and is conducive to maintaining the structural integrity of the silicon-carbon material and the electrode assembly under internal expansion and external extrusion conditions, further improving the first coulomb efficiency of the silicon-carbon material, and the high-temperature expansion inhibition performance and extrusion safety performance of the secondary battery.

[0033] The present application also provides a method for preparing the aforementioned porous carbon material, comprising the following steps:

[0034] Step S1, carbonizing a carbon precursor in an inert gas atmosphere to obtain a carbonized material;

[0035] Step S2, mixing the carbonized material and the pore-forming agent in a mass ratio of 1: (0.2-2.5) to obtain a mixture; then activating the mixture in an inert gas atmosphere to obtain an activated material; the activation treatment includes sequentially performing an activation treatment at T 1 Keep warm at t 1 Hours, T 2 Keep warm at t 2 Hours and T 3 Keep warm at t 3 Hour;

[0036] Step S3, washing the activated material with water and acid solution in turn, and filtering to obtain a porous carbon material.

[0037] In some embodiments, 700 ≤ T 1 ≤800,0.1≤t 1 ≤1; for example, T 1 A value selected from the range of 700, 710, 720, 740, 750, 760, 770, 780, 790, 800 or any two thereof, t 1 A value selected from the range of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or any two thereof.

[0038] In some embodiments, 800 < T 2 ≤900,4≤t 2 ≤7; for example, T 2A value selected from the range of 810, 820, 840, 850, 860, 870, 880, 890, 900 or any two thereof, t 2 A value selected from 4, 4.3, 4.6, 4.9, 5.3, 5.7, 6.0, 6.1, 6.4, 6.9, 7 or a range consisting of any two thereof.

[0039] In some embodiments, 900 < T 3 ≤1000,0.5≤t 3 ≤4; for example, a value selected from 910, 920, 930, 940, 950, 960, 970, 990, 1000 or a range consisting of any two of them, t 3 A value selected from the range consisting of 0.5, 0.8, 1.2, 1.4, 1.9, 2.3, 2.7, 3.1, 3.4, 3.7, 4 or any two thereof.

[0040] Based on the above scheme, the present application adopts a gradient insulation design during the activation treatment process, and utilizes the different reaction rates of the pore former and the carbonized material at different temperatures. By controlling the insulation time and temperature at different stages, it is possible to regulate the proportion and distribution of type I pores, type II pores and type III pores in the porous carbon material, thereby realizing the preparation of porous carbon materials with graded pore sizes, and further improving the first coulombic efficiency of silicon-carbon materials, as well as the high-temperature expansion inhibition performance and extrusion safety performance of secondary batteries.

[0041] In the present application, there is no special requirement for the selection of the carbon precursor, as long as it can meet the requirements of the present application, for example, it can be selected from at least one of a biomass precursor, a sugar precursor, a synthetic resin precursor or an asphalt precursor.

[0042] In some embodiments, the carbonization treatment is performed at a temperature of 600° C. to 1400° C. and for a time of 2 h to 8 h.

[0043] In some embodiments, the pore former can be selected from at least one of potassium hydroxide, potassium carbonate, potassium bicarbonate or potassium chloride, in particular at least one of potassium hydroxide, potassium carbonate or potassium bicarbonate, or a mixture of at least one of potassium hydroxide, potassium carbonate or potassium bicarbonate and potassium chloride.

[0044] In some embodiments, the molar concentration of hydrogen ions in the washing acid solution is 0.1 mol / L to 2 mol / L, and the acid solution can be selected from hydrochloric acid.

[0045] The present application also provides a silicon-carbon material, including a porous carbon material and a silicon material located in the pores of the porous carbon material; the porous carbon material includes any of the aforementioned porous carbon materials or the porous carbon material obtained by the aforementioned preparation method; the grain size of the silicon material is 0.9nm to 2nm. Exemplarily, the grain size of the silicon material is 0.9nm, 1.1nm, 1.2nm, 1.3nm, 1.4nm, 1.6nm, 1.7nm, 1.8nm, 1.9nm, 2nm or a value within the range composed of any two of them. The present application can limit the grain size of the silicon material and alleviate its volume expansion through the above-mentioned graded aperture structure, and it is also beneficial to improve the utilization rate of the silicon material in the electrochemical reaction and improve the first coulomb efficiency of the silicon-carbon material; and the above-mentioned graded aperture structure can also absorb and disperse stress and heat through the buffer space remaining after the deposition of the silicon material, enhance the structural stability of the silicon-carbon material, and improve the high-temperature expansion inhibition performance and extrusion safety performance of the secondary battery.

[0046] In some embodiments, the silicon carbon material further includes an amorphous carbon layer located on the surface of the porous carbon material.

[0047] The silicon-carbon material of the present application can be prepared by a method comprising the following steps:

[0048] The porous carbon material is placed in a rotary kiln, introduced into an inert atmosphere and heated to 450°C to 600°C, then introduced into silane gas for chemical vapor deposition, and kept warm for 2h to 8h, and finally the introduction of silane gas is stopped; then the temperature is raised to 500°C to 650°C in an inert atmosphere, then introduced into alkane gas and kept warm for 2h to 8h to obtain a silicon-carbon material, and then cooled to room temperature.

[0049] In some embodiments, the silane gas may be at least one of monosilane and disilane; the alkane gas may be at least one of methane, ethane, ethylene, and acetylene; the present application has no special requirements for the inert gas involved in the preparation, as long as it can meet the purpose of the present application, for example, the inert gas can be at least one of nitrogen, argon, and helium.

[0050] The present application also provides a secondary battery, comprising a positive electrode, a negative electrode and an electrolyte.

[0051] Secondary battery

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] positive electrode

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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 O 2 (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 (LiCoO 2 ), at least one of 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, the 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 electrode current collector and the positive electrode material layer, as long as the purpose of the present application can be achieved.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] negative electrode

[0068] 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.

[0069] In some embodiments, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes the aforementioned silicon-carbon material; the compaction density of the negative electrode material layer is 0.95 g / cm 3 Up to 1.05g / cm 3 For example, the compaction density of the negative electrode material layer is 0.95 g / cm 3 、0.96g / cm 3 , 0.97g / cm 3 、0.98g / cm 3 , 0.99g / cm 3 , 1.00g / cm 3 , 1.01g / cm3 , 1.02g / cm 3 , 1.03g / cm 3 , 1.04g / cm 3 , 1.05g / cm 3 Or a value within the range formed by any two of them. When the compaction density of the negative electrode material layer is further regulated within the above range, the energy density and internal buffer space of the secondary battery can be balanced, the wettability and contact efficiency of the silicon-carbon particles and the electrolyte can be improved, the internal expansion stress and the external extrusion stress can be dispersed, and the material crushing and lithium metal precipitation can be reduced, thereby further improving the first coulomb efficiency of the silicon-carbon material, as well as the high-temperature expansion suppression performance and extrusion safety performance of the secondary battery.

[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 active 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, SnO 2 , vanadium oxide, lithium vanadium oxide, etc., which can be doped or dedoped with lithium, or alloys thereof with lithium; or Si-C composites or Sn-C composites, etc., which contain the metal and carbon materials; or lithium titanate TiO 2 -Li 4 Ti5 O 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 active material, the negative electrode conductive agent, and the 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 active 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 propylene carbonate and ethylene carbonate, and the sum of the mass proportions of propylene carbonate and ethylene carbonate is E%, based on the mass of the electrolyte, and 10≤E≤30. Exemplarily, E can be 10, 11, 14, 17, 18, 20, 22, 25, 27, 29, 30 or a value in the range of any two thereof. Propylene carbonate and ethylene carbonate can promote the formation of a stable solid electrolyte interface film (SEI film), and the higher viscosity of the two is beneficial to improve the anti-extrusion ability of the battery, but the wettability of the electrolyte will be lost. The graded pore size structure of the porous carbon material of the present application can provide a suitable buffer space for the silicon material. By controlling the sum of the mass proportions of propylene carbonate and ethylene carbonate in the electrolyte to meet the above conditions, the viscosity of the electrolyte and the film-forming effect can be balanced. The above buffer space can also increase the diffusion path of lithium ions, and is conducive to promoting the formation of a more uniform, more stable and thinner SEI film on the surface of the silicon-carbon material, which can reduce the consumption of lithium ions in the electrolyte and reduce the side reactions between the silicon-carbon material and the electrolyte, which helps to further improve the first coulomb efficiency and improve the high-temperature expansion inhibition performance and extrusion safety performance of the secondary battery.

[0085] In some embodiments, based on the mass of the electrolyte, the mass proportion of propylene carbonate is 2% to 17%, and the mass proportion of ethylene carbonate is 6% to 16%.

[0086] In some embodiments, based on the mass of the electrolyte, the electrolyte includes lithium tetrafluoroborate, and the mass proportion of lithium tetrafluoroborate is S1%, 0.01≤S1≤0.8, preferably 0.05≤S1≤0.6. Exemplarily, S1 is 0.05, 0.10, 0.14, 0.20, 0.29, 0.35, 0.40, 0.45, 0.52, 0.59, 0.6 or a value within the range of any two thereof. The present application adopts lithium tetrafluoroborate in the electrolyte. When the mass proportion is within the above range, it can add boron-containing and fluorine-containing components to the SEI film on the surface of the silicon-carbon material, and cooperate with ethylene carbonate and propylene carbonate to improve the flexibility and density of the SEI film, reduce the breakage of the SEI film and the side reactions of the electrolyte, and further enhance the structural stability of the silicon-carbon material of the present application. In addition, by utilizing its higher ionic conductivity and the buffer space inside the silicon-carbon material, it can further improve the transmission rate of lithium ions and reduce or avoid the precipitation of lithium metal, thereby further improving the first coulomb efficiency of the secondary battery, inhibiting high-temperature expansion performance and extrusion safety performance.

[0087] In some embodiments, the electrolyte includes lithium bis(trifluoromethylsulfonyl)imide, and based on the mass of the electrolyte, the mass proportion of lithium bis(trifluoromethylsulfonyl)imide is S2%, 0.05≤S2≤2, preferably 0.1≤S2≤1.2. Exemplarily, S2 is a value within the range of 0.05, 0.20, 0.38, 0.58, 0.81, 0.97, 1.31, 1.46, 1.77, 1.86, 2 or any two thereof. The present application regulates the mass proportion of lithium bis(trifluoromethylsulfonyl)imide in the electrolyte to conform to the above range, and the combination with lithium tetrafluoroborate can further increase the content of inorganic substances such as LiF in the SEI film, improve the density, stability and ionic conductivity of the SEI film, thereby enhancing the SEI film's ability to transport lithium ions and its protective effect on silicon-carbon materials, and further improving the first coulomb efficiency of the secondary battery, the inhibition of high-temperature expansion performance and the extrusion safety performance.

[0088] According to some embodiments of the present application, lithium salts may also include but are not limited to: lithium hexafluorophosphate (LiPF 6 ), lithium difluorophosphate (LiPO 2 F 2 ), lithium bis(fluorosulfonyl)imide {Li(N(SO 2 F) 2 ), LiFSI}, lithium bis(oxalatoborate){LiB(C 2 O 4 ) 2 , LiBOB}, Lithium difluorooxalatoborate {LiBF 2 (C 2 O 4 )、LiDFOB}、LiNO 3 、LiClO4 、LiB(C 6 H 5 ) 4 、LiCH 3 SO 3 、LiCF 3 SO 3 、LiC(SO 2 CF 3 ) 3 , Li 2 SiF 6 or at least one of lithium difluoroborate. The present application does not limit the content of lithium salt in the electrolyte, as long as the purpose of the present application can be achieved.

[0089] 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 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.

[0090] Electronic Devices

[0091] The present application provides an electronic device including the above-mentioned secondary battery. 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 notebook computer, a pen input computer, a mobile computer, an e-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 physical properties mentioned in this application can be measured by the following methods, and the physical properties in the following examples and comparative examples are measured by the following methods.

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

[0095] The porous carbon material was tested using a physical adsorption instrument (model: ipore 620). The process included: taking 0.15 g of porous carbon material 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 relative pressures, thereby drawing the isothermal adsorption curve of the sample and calculating the single-point adsorption pore volume of the sample as the pore volume of the porous carbon material; using NLDFT to calculate the pore size distribution, and then calculating the volume percentage of type I pores, type II pores, and type III pores.

[0096] Elastic modulus test:

[0097] The Shimadzu single particle crusher (FLAT50) was used to measure particles with a size of 8 to 10 μm for crushing force testing, with a minimum / maximum pressure of 0.02 / 10 mN. The elastic modulus of the sample was calculated based on the corresponding deformation and approximate contact surface under the maximum pressure, and using Hooke's law and pressure formula.

[0098] Grain size test:

[0099] The XRD powder diffractometer (model: BRUKER D8 Advance) was used with a Cu target. Test the target material: Take the porous carbon material as the sample to be tested, sieve the sample with a 200-mesh sieve, then take the powder under the sieve and put it into the sample pool, then flatten the surface, clean up the excess powder around it, put the prepared sample to be tested into the XRD ray powder diffractometer, test the sample to be tested, and collect the XRD spectrum. Based on the measured XRD spectrum, find the half-peak width and crystal plane spacing corresponding to the diffraction peak of the silicon (111) or (220) plane, use the Bragg equation to calculate the diffraction angle, and then calculate the size of the silicon grains according to the Sherman equation D=Kλ / βcosθ.

[0100] First coulombic efficiency test:

[0101] Electrode preparation: The silicon-carbon material of the embodiment or comparative example is used as the negative electrode active material, and the negative electrode active material, the conductive agent (carbon nanotube (CNT)), the binder (polymethyl acrylate), and the thickener (sodium carboxymethyl cellulose (CMC)) are fully stirred and mixed in a solvent deionized water at a weight ratio of 95.7:1.5:1.8:1 to form a uniform negative electrode slurry. The negative electrode slurry is evenly coated on the negative electrode current collector copper foil, dried, and then cold pressed to form a negative electrode active material layer, and then cut into pieces and welded to the pole ears to obtain a negative electrode sheet.

[0102] Button battery assembly: Using metallic lithium as the counter electrode, a metallic lithium sheet with a diameter of 18 mm and a thickness of 0.6 mm, a diaphragm (a porous polyethylene film of 12 μm), and the negative electrode sheets in each embodiment and comparative example (cut into a diameter of 18 mm for use) are assembled and stacked in sequence, and the electrolyte corresponding to the embodiment or comparative example is added, and the positive and negative electrodes are packaged in button-type stainless steel shells to obtain a button battery.

[0103] At 25°C, after the button cell was left to stand for 4 hours, it was discharged to 5mV at a constant current of 0.02C. After standing for 5 minutes, it was charged to 2.0V at a constant current of 0.02C. The first cycle charging capacity and the first cycle discharge capacity were recorded. The first coulomb efficiency first cycle = the first cycle charging capacity / the first cycle discharge capacity.

[0104] High temperature cycle thickness test:

[0105] Place the lithium-ion full battery in a constant temperature box at 25°C ± 1°C for 30 minutes and record the initial thickness H of the lithium-ion full battery. 0 The lithium-ion battery was placed in a constant temperature box at 45℃±1℃ for 60 minutes, and the charge and discharge test was performed under the following conditions: 0.5C constant current charge to 4.53V, then 4.53V constant voltage charge to 0.025C, let stand for 5 minutes, and then 0.5C discharge to 3.0V. This is a charge and discharge cycle. The above cycle process was repeated for 500 cycles. The thickness H after the 500th cycle was recorded. 1 .

[0106] Cycle expansion ratio = (H 1 -H 0 ) / H 0 ×100%.

[0107] Screw compression test:

[0108] The lithium-ion full battery of each embodiment or comparative example was placed in a constant temperature box at 25°C for 30 minutes, and then the charge and discharge test was performed under the following conditions: charging to 4.53V at a constant current of 0.5C, then charging to 0.025C at a constant voltage of 4.53V, and then placed for 5 minutes, and then discharged to 3.0V at 0.5C, which is one charge and discharge cycle process. The above cycle process was repeated 100 times.

[0109] Then place the lithium-ion full battery on the pressure plate, and place a test screw on the surface of the lithium-ion full battery. Then use a pressure device to apply pressure perpendicular to the direction of the plate, and apply a 13kN extrusion force between the two pressure plates, including: using a preload force of 20N as the starting pressure recording point, an extrusion speed of 15kN / min, and stopping the test when the pressure reaches 13kN. If the lithium-ion full battery does not catch fire or explode, it indicates that it has passed the screw extrusion test. Each time, 10 lithium-ion full batteries are tested in parallel according to the above steps, and the number of tests that pass the test is recorded. For example, 4 / 10 means that 4 out of the 10 tested lithium-ion full batteries passed the screw extrusion test.

[0110] 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.

[0111] Example 1-1

[0112] Preparation method of silicon carbon material:

[0113] Step S1, putting 1 kg of synthetic resin carbon precursor into an oven, introducing nitrogen, excluding air and heating to 600° C., keeping the temperature for 3 hours, and cooling to obtain a carbonized material;

[0114] Step S2, after mixing the carbonized material and the pore-forming agent in a mass ratio of 1:1.2, the mixture is placed in a rotary kiln, nitrogen is introduced, the air is excluded, the temperature is raised to 750°C and kept for 0.3h, then the temperature is raised to 860°C and kept for 5h, and finally the temperature is raised to 950°C and kept for 1h, and the activated material is obtained after cooling;

[0115] Step S3, washing the activated material with 10L of water, then washing with 10L of 1mol / L hydrochloric acid solution, filtering, and drying to obtain a porous carbon material;

[0116] Step S4, placing the porous carbon into a rotary kiln, introducing an inert atmosphere to heat up to 500°C, then introducing monosilane gas and keeping it warm for 4 hours for chemical vapor deposition, finally turning off the monosilane gas, keeping it warm at 550°C for 4 hours with methane gas, and obtaining silicon-carbon material after cooling to room temperature.

[0117] Preparation of negative electrode:

[0118] Silicon-carbon material and artificial graphite are mixed in a mass ratio of 1:9 to obtain negative electrode active material. The negative electrode active material (95wt%), conductive carbon black (0.5wt%), polymethyl acrylate (3.5%), and 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 (97wt%), conductive carbon black (1.5wt%), and polyvinylidene fluoride (1.5wt%) are dissolved in N-methylpyrrolidone to prepare positive electrode slurry. The positive electrode slurry is evenly coated on one surface of the aluminum foil, and the coating step is 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 is dried, pressurized, and cut into a specified size, and the tabs are welded to make the positive electrode.

[0121] Preparation of diaphragm: A 7 μm thick polyethylene / polypropylene composite porous 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, dimethyl carbonate and diethyl carbonate (mass ratio 1:1) were mixed to obtain a basic solvent, and then propylene carbonate, ethylene carbonate, fluoroethylene carbonate, 1,3-propane sultone and lithium hexafluorophosphate were added to the above-mentioned basic solvent, and the electrolyte was obtained after mixing evenly. Based on the mass of the electrolyte, the mass proportion of propylene carbonate is 12%, the mass proportion of ethylene carbonate is 6%, the mass proportion of fluoroethylene carbonate is 12%, the mass proportion of 1,3-propane sultone is 1%, and the mass proportion of lithium hexafluorophosphate is 12.5%.

[0124] 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 battery is obtained.

[0126] Example 1-2 to Example 1-12, Comparative Example 1-1 to Comparative Example 1-3

[0127] The only difference from Example 1-1 is that, according to Table 1, in the porous carbon material, based on the sum of the pore volumes of the first type of pores, the second type of pores and the third type of pores, the volume proportion V of the first type of pores is 1 %, the volume proportion of the second type of pores V 2 % and the volume proportion of the three types of pores V 3 %, the pore volume and elastic modulus of the porous carbon material, the grain size of the silicon material in the silicon-carbon material, and the compaction density of the negative electrode material layer are adjusted. The specific adjustment parameters and performance test results are shown in Table 1. Among them, by adjusting the temperature and time of the gradient insulation treatment during the activation treatment, the volume proportion of the first type of pores, the second type of pores, and the third type of pores can be adjusted. For example, within the scope of the requirements of this application, the T 1 Temperature and / or extension t 1 Can increase the volume proportion of a type of pores; improve T 2 Temperature and / or extension t 2 Can increase the volume proportion of type II pores; reduce T 3 temperature and / or shortening t 3 The volume proportion of the three types of pores can be reduced; in the activation treatment of Comparative Example 1-2, only two stages of gradient heat preservation treatment were used, and no T 3 Insulation treatment of the section.

[0128] Table 1

[0129]

[0130]

[0131] As shown in Table 1, the present invention regulates the porous carbon material to include type I pores, type II pores and type III pores, and the volume proportion of type I pores is V 1 % and the volume proportion of type II pores V 2 %Satisfy 0.1≤V 1 ≤10,50≤V 2 ≤95, which can improve the first coulombic efficiency of the silicon-carbon material and improve the high-temperature expansion suppression and extrusion safety performance of the secondary battery. In particular, the porous carbon material satisfies at least one of the following conditions: (1) 0.5≤V 1 ≤10; (2) 50 ≤ V 2≤85; (3)5≤V 3 ≤45; (4) 0.1 ≤ V 1 / V 3 ≤20, which can improve the coordination effect of type I pores, type II pores and type III pores, thereby further improving the first coulombic efficiency of silicon-carbon materials, as well as the high-temperature expansion inhibition performance and extrusion safety performance of secondary batteries.

[0132] In particular, when the pore volume of the porous carbon material is 0.50 cm 3 / g to 1.0cm 3 / g, can further improve the first coulombic efficiency of the secondary battery, inhibit high temperature expansion performance and extrusion safety performance. In particular, when the elastic modulus of the porous carbon material is 1GPa to 50GPa, especially in the range of 23GPa to 44GPa, can further improve the first coulombic efficiency of the secondary battery, inhibit high temperature expansion performance and extrusion safety performance.

[0133] In particular, the grain size of the silicon material is 0.9nm to 2nm, which can improve the first coulombic efficiency of the silicon-carbon material and improve the high-temperature expansion suppression and extrusion safety performance of the secondary battery. In particular, the compaction density of the negative electrode material layer is adjusted to 0.95g / cm 3 Up to 1.05g / cm 3 , which can further improve the first coulombic efficiency of silicon-carbon materials, as well as the high-temperature expansion inhibition performance and extrusion safety performance of secondary batteries.

[0134] Example 2-1 to Example 2-9

[0135] The only difference compared with Example 1-1 is that the mass ratio of propylene carbonate and ethylene carbonate in the electrolyte is adjusted according to Table 2, lithium tetrafluoroborate accounting for S1% by mass and / or lithium bis(trifluoromethylsulfonyl)imide accounting for S2% by mass is further added to the electrolyte, and the content of the base solvent is adaptively adjusted, wherein the mass ratio of dimethyl carbonate and diethyl carbonate remains unchanged, and the specific adjustment parameters and performance test results are shown in Table 2 below.

[0136] Table 2

[0137]

[0138] As can be seen from Table 2, the present application controls the electrolyte to include propylene carbonate and ethylene carbonate, and regulates the sum of the mass proportions of propylene carbonate and ethylene carbonate in the electrolyte E% to satisfy 10≤E≤30, which can further improve the first coulombic efficiency, as well as improve the secondary battery's high-temperature expansion suppression performance and extrusion safety performance.

[0139] In particular, the present application regulates the electrolyte to include lithium tetrafluoroborate and its mass proportion S1% to meet 0.01≤S1≤0.8, which can further improve the initial coulombic efficiency, high temperature expansion suppression performance and extrusion safety performance of the secondary battery. In particular, when 0.05≤S1≤0.6 is met, the initial coulombic efficiency, high temperature expansion suppression performance and extrusion safety performance of the secondary battery can be further improved.

[0140] In particular, the present application regulates the electrolyte to include lithium bis(trifluoromethylsulfonyl)imide and its mass proportion S2% to meet 0.05≤S2≤2, which can further improve the initial coulombic efficiency, high temperature expansion suppression performance and extrusion safety performance of the secondary battery. In particular, when 0.1≤S2≤1.2 is met, the initial coulombic efficiency, high temperature expansion suppression performance and extrusion safety performance of the secondary battery can be further improved.

[0141] 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 porous carbon material, characterized in that: The porous carbon material includes type I pores, type II pores and type III pores; the pore size of type I pores is P1 nm, 0<P1≤1; the pore size of type II pores is P2 nm, 1<P2≤3; the pore size of type III pores is P3 nm, 3<P3≤10; Based on the sum of the pore volumes of the first type of pores, the second type of pores and the third type of pores, the volume proportion of the first type of pores is V1%, the volume proportion of the second type of pores is V2%, and the volume proportion of the third type of pores is V3%; 0.1≤V1≤10, 50≤V2≤95.

2. The porous carbon material according to claim 1, characterized in that The porous carbon material satisfies at least one of the following conditions: (1)0.5≤V1≤10； (2)50≤V2≤85； (3)5≤V3≤45； (4)0.1≤V1 / V3≤20.

3. The porous carbon material according to claim 1 or 2, characterized in that: The pore volume of the porous carbon material is 0.50 cm 3 / g to 1.0cm 3 / g; and / or, The elastic modulus of the porous carbon material is 1 GPa to 50 GPa, preferably 23 GPa to 44 GPa.

4. A method for preparing a porous carbon material according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step S1, carbonizing a carbon precursor in an inert gas atmosphere to obtain a carbonized material; Step S2, mixing the carbonized material and the pore-forming agent in a mass ratio of 1:(0.2-2.5) to obtain a mixture; then activating the mixture in an inert gas atmosphere to obtain an activated material; the activation treatment comprises sequentially keeping warm at T1°C for t1 hour, keeping warm at T2°C for t2 hours, and keeping warm at T3°C for t3 hours; wherein, 700≤T1≤800, 0.1≤t1≤1; 800<T2≤900, 4≤t2≤7; 900<T3≤1000, 0.5≤t3≤4; Step S3, washing the activated material with water and acid solution in sequence, and filtering to obtain the porous carbon material.

5. A silicon-carbon material, characterized in that: Comprising a porous carbon material and a silicon material located in the pores of the porous carbon material; the porous carbon material comprises the porous carbon material according to any one of claims 1 to 3 or the porous carbon material prepared by the preparation method according to claim 4; The grain size of the silicon material is 0.9 nm to 2 nm.

6. A secondary battery, characterized in that: It comprises a positive electrode, a negative electrode and an electrolyte; the negative electrode comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector; the negative electrode material layer comprises the silicon-carbon material according to claim 5; The compaction density of the negative electrode material layer is 0.95 g / cm 3 Up to 1.05g / cm 3 .

7. The secondary battery according to claim 6, characterized in that: The electrolyte includes propylene carbonate and ethylene carbonate. Based on the mass of the electrolyte, the sum of the mass proportions of the propylene carbonate and the ethylene carbonate is E%, and 10≤E≤30.

8. The secondary battery according to claim 7, characterized in that: The electrolyte includes lithium tetrafluoroborate. Based on the mass of the electrolyte, the mass proportion of the lithium tetrafluoroborate is S1%, 0.01≤S1≤0.8, and preferably 0.05≤S1≤0.

6.

9. The secondary battery according to claim 8, characterized in that: The electrolyte includes lithium bis(trifluoromethylsulfonyl)imide. Based on the mass of the electrolyte, the mass proportion of the lithium bis(trifluoromethylsulfonyl)imide is S2%, 0.05≤S2≤2, and preferably 0.1≤S2≤1.

2.

10. An electronic device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 6 to 9.

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