A negative electrode material, a preparation method thereof, a secondary battery, and an electronic device

Abstract

The application provides a negative electrode material and a preparation method thereof, a secondary battery and an electronic device. The negative electrode material is prepared by the following method: (1) placing a porous carrier carbon material in a sealed cavity for heat treatment, the temperature of the heat treatment being a temperature T1 of thermal decomposition of a silicon source, T1 being 400 DEG C to 600 DEG C; (2) introducing a first gas containing the silicon source to deposit a deposited silicon material on the porous carrier carbon material, wherein the flow rate L1 of the first gas introduced is 3 L / min to 5 L / min, the time t1 is 140 min to 450 min, and the pressure P1 in the sealed cavity is 70 KPa to 90 KPa; and (3) then introducing a second gas containing a carbon source to react to obtain the negative electrode material, wherein the flow rate L2 of the second gas introduced is 5 L / min to 7 L / min, the time t2 is 300 min to 480 min, and the pressure P2 in the sealed cavity is 5 KPa to 20 KPa. The negative electrode material prepared by the above method and the application of the negative electrode material in the secondary battery can improve the cycle performance of the secondary battery.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a negative electrode material and its preparation method, a secondary battery, and an electronic device. Background Technology

[0002] With the rapid promotion of new energy sources such as electric vehicles, photovoltaic power generation, and wind power, the demand for storing these energy sources using lithium-ion batteries is also increasing. The negative electrode material of a lithium-ion battery has a crucial impact on the overall battery performance. Silicon-carbon composite materials are a type of lithium-ion battery negative electrode material with excellent electrochemical properties, enabling high capacity, long lifespan, and excellent fast charge / discharge performance.

[0003] However, the current use of silicon-carbon composite materials has problems such as excessive volume expansion and low conductivity, which can affect the cycle performance of lithium-ion batteries. Summary of the Invention

[0004] The purpose of this application is to provide a negative electrode material and its preparation method, a secondary battery, and an electronic device to improve the cycle performance of the secondary battery. The specific technical solution is as follows:

[0005] The first aspect of this application provides a method for preparing a negative electrode material, which includes the following steps:

[0006] (1) The porous carrier carbon material is placed in a sealed cavity for heat treatment. The heat treatment temperature is the temperature of silicon source thermal decomposition T1, where T1 is 400℃ to 600℃.

[0007] (2) A porous carrier carbon material containing the silicon source is deposited by introducing a first gas to obtain a silicon material, wherein the flow rate L1 of the first gas is 3L / min to 5L / min, the time t1 is 140min to 450min, and the pressure P1 in the sealed cavity is 70KPa to 90KPa.

[0008] (3) Then a second gas containing a carbon source is introduced to react and obtain the negative electrode material, wherein the flow rate L2 of the second gas is 5 L / min to 7 L / min, the time t2 is 300 min to 480 min, and the pressure P2 in the sealed cavity is 5 kPa to 20 kPa.

[0009] The above methods can increase the speed and quantity of silicon source gas molecules entering the porous carbon support material, thereby avoiding the decomposition and deposition of silicon source gas on the surface of the porous carbon support material. This effectively prevents the enrichment of silicon on the surface of silicon-carbon composite particles, allowing silicon to be uniformly distributed within the pores of the porous carbon support material. The pores of the porous carbon support material provide buffer space for the expansion of silicon, and the framework of the porous carbon support material can isolate silicon from the electrolyte, reducing the occurrence of side reactions. This makes the silicon-carbon composite material less prone to expansion. When applied to secondary batteries, the above silicon-carbon composite material can improve the cycle performance of the secondary battery; it can also improve the stability of the silicon-carbon composite material and give it good conductivity, further improving the cycle performance of the secondary battery. Furthermore, the above methods are environmentally friendly, simple in process, and conducive to the large-scale production of high-performance silicon-carbon composite materials.

[0010] In one embodiment of this application, the porous carrier carbon material includes at least one of biomass-derived carbon, resin-derived carbon, petroleum coke-derived carbon, coal-derived carbon, metal-modified carbon material, or metal oxide-modified carbon material; the metal includes at least one of Fe, Co, Pd, Zn, or Al; and the resin-derived carbon includes at least one of phenolic resin carbon, polyethylene carbon, or epoxy resin carbon. By selecting the above-mentioned porous carrier carbon material, the pores of the porous carrier carbon material can provide buffer space for the expansion of silicon material, thereby making the prepared silicon-carbon composite material less prone to expansion and further improving the cycle performance of the secondary battery.

[0011] In one embodiment of this application, the silicon source includes at least one of silane, disilane, or propane. By selecting the above-mentioned silicon source, the silicon material can be uniformly distributed within the pores of the porous carrier carbon material, thereby making the prepared silicon-carbon composite material less prone to expansion and further improving the cycle performance of the secondary battery.

[0012] In one embodiment of this application, the carbon source includes at least one selected from acetylene, ethylene, propylene, propane, or methane. By selecting the above-mentioned carbon source, carbon materials can be uniformly distributed on the surface of the porous carrier carbon material on which silicon materials are deposited, thereby improving the conductivity of the silicon-carbon composite material and enhancing the cycle performance of the secondary battery.

[0013] In one embodiment of this application, it satisfies at least one of the following features:

[0014] (1) The first gas further includes an inert gas, and the volume percentage of the silicon source is 40% to 60% based on the volume of the first gas;

[0015] (2) The second gas also includes an inert gas, and the carbon source has a volume percentage of 40% to 60% based on the volume of the second gas.

[0016] A second aspect of this application provides a negative electrode material prepared according to any of the foregoing embodiments, wherein the negative electrode material is a silicon-carbon composite material, the silicon-carbon composite material comprising a porous carrier carbon material, silicon material disposed within the pores of the porous carrier carbon material, and carbon material disposed on at least a portion of the surface of the porous carrier carbon material. Therefore, the negative electrode material provided by this application is not easily expanded and has good electrical conductivity.

[0017] In one embodiment of this application, the Raman spectrum of the silicon-carbon composite material is at 476±8 cm⁻¹. -1 There is a characteristic peak of amorphous silicon at 1360±20 cm⁻¹. -1 The characteristic D band peak of carbon is located at 1580±20 cm⁻¹. -1 The amorphous silicon has a carbon G-band characteristic peak at a certain location, and the intensity I of the characteristic peak is... Si The intensity I of the characteristic peak of the D band of the carbon D The ratio I Si / I D The intensity I of the characteristic peak of the amorphous silicon is between 0.15 and 0.98. Si The intensity I of the characteristic peak of the G band of the carbon G The ratio I Si / I G The values ​​ranged from 0.16 to 1.20. By adjusting the Raman spectrum of the silicon-carbon composite material, characteristic peaks were observed at the aforementioned positions, and I... Si / I D and I Si / I G The value is within the scope of this application, indicating that the silicon-carbon composite material has a suitable silicon content and carbon coating amount, which can effectively reduce the volume expansion of particles, and also weaken the SEI film thickness increase and active lithium consumption caused by the side reaction between silicon material and electrolyte, thereby improving the specific capacity and first coulombic efficiency of silicon-carbon composite material and improving the cycle performance of secondary battery.

[0018] In one embodiment of this application, the silicon content in the silicon-carbon composite material is between 20% and 55% by mass, based on the mass of the composite material. By controlling the silicon content in the silicon-carbon composite material within the range of this application, the volume expansion of the silicon-carbon composite material can be reduced, the cycle performance of the secondary battery can be improved, and the secondary battery can have a higher energy density.

[0019] In one embodiment of this application, the pore volume of the porous carrier carbon material is 0.8 cm³. 3 / g to 1.1cm 3 / g, the porous carrier carbon material includes macropores, mesopores, and micropores, and based on the pore volume of the porous carrier carbon material, the proportion of the micropore volume is ≥80%. By controlling the pore volume of the porous carrier carbon material and the proportion of the micropore volume within the scope of this application, the pores of the porous carrier carbon material can provide sufficient buffer space for the expansion of the silicon material, thereby making the silicon-carbon composite material less prone to expansion and further improving the cycle performance of the secondary battery. In one embodiment of this application, the proportion of the micropore volume is ≥90%, which can further improve the cycle performance of the secondary battery.

[0020] In one embodiment of this application, the silicon-carbon composite material satisfies at least one of the following characteristics: (1) Dv50 is 4 μm to 8 μm; (2) Dv99 is 16 μm to 25 μm; (3) Dn10 is 0.5 μm to 3 μm; (4) specific surface area is 0.5 m². 2 / g to 8m 2 / g.

[0021] A third aspect of this application provides a secondary battery comprising a positive electrode, a negative electrode, and a separator. The negative electrode includes a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector. The negative electrode material layer comprises the negative electrode material described in any of the foregoing embodiments. Therefore, the secondary battery provided by this application has good cycle performance.

[0022] A fourth aspect of this application provides an electronic device that includes a secondary battery as described in any of the foregoing embodiments. Therefore, the electronic device provided by this application has good performance characteristics.

[0023] The beneficial effects of this application are:

[0024] This application provides a negative electrode material, its preparation method, a secondary battery, and an electronic device. The negative electrode material is prepared by the following method: (1) a porous carrier carbon material is placed in a sealed cavity for heat treatment at a temperature equal to the silicon source thermal decomposition temperature T1, where T1 is 400°C to 600°C; (2) a first gas containing a silicon source is introduced to deposit a porous carrier carbon material containing silicon, wherein the flow rate L1 of the first gas is 3L / min to 5L / min, the time t1 is 140min to 450min, and the pressure P1 in the sealed cavity is 70KPa to 90KPa; (3) a second gas containing a carbon source is then introduced to react and obtain the negative electrode material, wherein the flow rate L2 of the second gas is 5L / min to 7L / min, the time t2 is 300min to 480min, and the pressure P2 in the sealed cavity is 5KPa to 20KPa. The negative electrode material prepared by the above method, and its application in a secondary battery, can improve the cycle performance of the secondary battery.

[0025] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0027] Figure 1 These are the Raman spectra of Example 7 and Comparative Example 1 of this application. Detailed Implementation

[0028] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0029] It should be noted that, in the following explanation, lithium-ion batteries are used as an example of secondary batteries to illustrate this application; however, the secondary batteries in this application are not limited to lithium-ion batteries. The specific technical solution is as follows:

[0030] To address the cycling stability issue of silicon anodes, current technologies employ composites of silicon and porous carbon materials to reduce silicon expansion and associated side reactions. However, these composite materials often exhibit a high silicon content on their surface, with some particles having a higher silicon abundance on the surface than inside. When the surface silicon comes into contact with the electrolyte, it leads to repeated rupture and repair of the solid electrolyte interphase (SEI) film, as well as expansion followed by breakage and peeling, ultimately resulting in a decline in the cycle performance of the secondary battery.

[0031] The first aspect of this application provides a method for preparing a negative electrode material, which includes the following steps:

[0032] (1) The porous carrier carbon material is placed in a sealed cavity for heat treatment. The heat treatment temperature is the temperature of silicon source thermal decomposition T1, where T1 is 400℃ to 600℃.

[0033] (2) A porous carrier carbon material containing silicon source is deposited by introducing a first gas containing silicon source to obtain a silicon material. The flow rate L1 of the first gas is 3L / min to 5L / min, the time t1 is 140min to 450min, and the pressure P1 in the sealed cavity is 70KPa to 90KPa.

[0034] (3) Then a second gas containing a carbon source is introduced to react and obtain the negative electrode material. The flow rate L2 of the second gas is 5 L / min to 7 L / min, the time t2 is 300 min to 480 min, and the pressure P2 in the sealed cavity is 5 kPa to 20 kPa.

[0035] For example, T1 can be 400℃, 420℃, 440℃, 460℃, 480℃, 500℃, 520℃, 540℃, 560℃, 580℃, 600℃, or a range of any two of the above values. L1 can be 3L / min, 3.2L / min, 3.4L / min, 3.6L / min, 3.8L / min, 4L / min, 4.2L / min, 4.4L / min, 4.6L / min, 4.8L / min, 5L / min, or a range of any two of the above values. t1 can be 140 min, 160 min, 180 min, 200 min, 220 min, 240 min, 260 min, 280 min, 300 min, 320 min, 340 min, 360 min, 380 min, 400 min, 420 min, 440 min, 450 min, or a range of any two of the above values. P1 can be 70 kPa, 71 kPa, 72 kPa, 73 kPa, 74 kPa, 75 kPa, 76 kPa, 77 kPa, 78 kPa, 79 kPa, 80 kPa, 81 kPa, 82 kPa, 83 kPa, 84 kPa, 85 kPa, 86 kPa, 87 kPa, 88 kPa, 89 kPa, 90 kPa, or a range of any two of the above values. L2 can be 5 L / min, 5.2 L / min, 5.4 L / min, 5.6 L / min, 5.8 L / min, 6 L / min, 6.2 L / min, 6.4 L / min, 6.6 L / min, 6.8 L / min, 7 L / min, or a range of any two of the above values. t2 can be 300 min, 320 min, 340 min, 360 min, 380 min, 400 min, 420 min, 440 min, 460 min, 480 min, or a range of any two of the above values. P2 can be 5 kPa, 6 kPa, 7 kPa, 8 kPa, 9 kPa, 10 kPa, 11 kPa, 12 kPa, 13 kPa, 14 kPa, 15 kPa, 16 kPa, 17 kPa, 18 kPa, 19 kPa, 20 kPa, or a range of any two of the above values.

[0036] This application does not impose any particular limitation on the method of heat treatment of porous carbon support materials placed in a sealed cavity, as long as the purpose of this application can be achieved. For example, the porous carbon support material can be added to a fluidized bed, the stirring speed can be controlled, nitrogen gas can be introduced to make the porous carbon support material reach a fluidized state, and then heating can be performed. The stirring speed can be from 50 rpm to 250 rpm, and the nitrogen gas flow rate can be from 5 L / min to 15 L / min.

[0037] The inventors discovered that when preparing silicon-carbon composite materials using chemical vapor deposition, the amount of silicon material deposited on the porous carrier carbon material can be controlled by adjusting the introduction time of the first gas containing silicon source. Simultaneously, adjusting the pressure of the sealed cavity induces the silicon source gas to decompose and deposit inside the porous carrier carbon material. This method increases the speed and quantity of silicon source gas molecules entering the porous carrier carbon material, thus preventing the decomposition and deposition of silicon source gas on the surface of the porous carrier carbon material. This effectively prevents the enrichment of silicon on the surface of the silicon-carbon composite material particles, allowing for uniform distribution of silicon material within the pores of the porous carrier carbon material. The pores of the porous carrier carbon material provide buffer space for the expansion of silicon material, and the framework of the porous carrier carbon material isolates silicon material from the electrolyte, reducing side reactions and making the silicon-carbon composite material less prone to expansion. Applying this silicon-carbon composite material to secondary batteries can improve the cycle performance of the secondary batteries. Then, a second gas containing a carbon source is introduced. By adjusting the introduction time of the second gas and the pressure in the sealed cavity, carbon material is deposited on the surface of the porous carrier carbon material for silicon deposition. This carbon material isolates the silicon material from the external environment, preventing it from reacting with water or air, thus improving the stability of the silicon-carbon composite material. It also imparts good electrical conductivity to the silicon-carbon composite material, improving the cycle performance of the secondary battery. Furthermore, the above method is environmentally friendly, simple in process, and conducive to the large-scale production of high-performance silicon-carbon composite materials.

[0038] In one embodiment of this application, the porous carrier carbon material includes at least one of biomass-derived carbon, resin-derived carbon, petroleum coke-derived carbon, coal-derived carbon, metal-modified carbon materials, or metal oxide-modified carbon materials; the metal includes at least one of Fe, Co, Pd, Zn, or Al, and the resin-derived carbon includes at least one of phenolic resin carbon, polyethylene carbon, or epoxy resin carbon. By selecting the above-mentioned porous carrier carbon material, the pores of the porous carrier carbon material can provide buffer space for the expansion of silicon material, thereby making the prepared silicon-carbon composite material less prone to expansion and further improving the cycle performance of the secondary battery. In this application, biomass-derived carbon includes coconut shell carbon, corn starch carbon, or corn stalk carbon, etc. Petroleum coke-derived carbon includes needle coke, sponge coke, or low-sulfur coke, etc. Coal-derived carbon includes anthracite carbon, lignite carbon, or bituminous coal carbon, etc. In this application, phenolic resin carbon is a material obtained by carbonizing phenolic resin, and the same applies to other carbon materials.

[0039] In one embodiment of this application, the silicon source includes at least one of silane, disilane, or propane. By selecting the above-mentioned silicon source, the silicon material can be uniformly distributed within the pores of the porous carrier carbon material, thereby making the prepared silicon-carbon composite material less prone to expansion and further improving the cycle performance of the secondary battery. In this application, when the silicon source contains two or more of the above-mentioned substances, there is no particular limitation on the ratio between the substances, as long as the purpose of this application can be achieved.

[0040] In one embodiment of this application, the carbon source includes at least one selected from acetylene, ethylene, propylene, propane, or methane. By selecting the above-mentioned carbon source, the carbon material can be uniformly distributed on the surface of the porous carrier carbon material on which the silicon material is deposited, thereby improving the conductivity of the silicon-carbon composite material and enhancing the cycle performance of the secondary battery. In this application, when the carbon source contains two or more of the above-mentioned substances, there is no particular limitation on the ratio between the substances, as long as the purpose of this application can be achieved.

[0041] In one embodiment of this application, the first gas further includes an inert gas, and the volume percentage of the silicon source is 40% to 60% based on the volume of the first gas. Exemplarily, the volume percentage of the silicon source can be 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, or a range of any two of the above values. By controlling the volume percentage of the silicon source in the first gas within the scope of this application, the prepared silicon-carbon composite material can have a suitable silicon content and fewer impurities, thereby enabling the secondary battery to have both good cycle performance and high energy density.

[0042] In one embodiment of this application, the second gas further includes an inert gas, and the volume percentage of the carbon source is 40% to 60% based on the volume of the second gas. Exemplarily, the volume percentage of the carbon source can be 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, or a range consisting of any two of the above values. By controlling the volume percentage of the carbon source in the second gas within the scope of this application, the prepared silicon-carbon composite material can have a suitable carbon content and fewer impurities, thereby enabling the secondary battery to have better cycle performance.

[0043] This application does not impose any particular restrictions on the inert gas, as long as it can achieve the purpose of this application. For example, the inert gas can be at least one of argon or helium.

[0044] The second aspect of this application provides a negative electrode material prepared by any of the foregoing embodiments, wherein the negative electrode material is a silicon-carbon composite material, the silicon-carbon composite material comprising a porous carrier carbon material, silicon material disposed within the pores of the porous carrier carbon material, and carbon material disposed on at least a portion of the surface of the porous carrier carbon material. The negative electrode material prepared by the above preparation method has silicon material uniformly distributed within the pores of the porous carrier carbon material and carbon material on its surface, which makes the negative electrode material less prone to expansion, provides good conductivity, and improves the cycle performance of the secondary battery when applied to it.

[0045] In one embodiment of this application, the Raman spectrum of the silicon-carbon composite material is at 476±8 cm⁻¹. -1 There is a characteristic peak of amorphous silicon at 1360±20 cm⁻¹. -1 The characteristic D band peak of carbon is located at 1580±20 cm⁻¹. -1 The characteristic G-band peak of carbon is present, while the intensity of the characteristic peak of amorphous silicon is I. Si The intensity of the characteristic peak of the D band of carbon (I) D The ratio I Si / I D The intensity I of the characteristic peak of amorphous silicon ranges from 0.15 to 0.98. Si The intensity of the characteristic peak of the G band of carbon (I) G The ratio I Si / I G It ranges from 0.16 to 1.20. For example, I Si / I D It can be 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 0.98, or a range of any two of the above values. Si / I G The possible values ​​are 0.16, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, 0.34, 0.36, 0.38, 0.4, 0.42, 0.44, 0.46, 0.48, 0.5, 0.52, 0.54, 0.56, 0.58, 0.6, 0.62, 0.64, 0.66, 0.68, and 0. 7, 0.72, 0.74, 0.76, 0.78, 0.8, 0.82, 0.84, 0.86, 0.88, 0.9, 0.92, 0.94, 0.96, 0.98, 1, 1.02, 1.04, 1.06, 1.08, 1.1, 1.12, 1.14, 1.16, 1.18, 1.20, or a range consisting of any two of the above values. By adjusting the Raman spectrum of the silicon-carbon composite material to have characteristic peaks at the above positions and ISi / I D and I Si / I G The value is within the scope of this application, indicating that the silicon-carbon composite material has a suitable silicon content and carbon coating amount, which can effectively reduce the volume expansion of particles, and also weaken the SEI film thickness increase and active lithium consumption caused by the side reaction between silicon material and electrolyte, thereby improving the specific capacity and first coulombic efficiency of silicon-carbon composite material and improving the cycle performance of secondary battery.

[0046] In one embodiment of this application, the mass percentage of silicon in the silicon-carbon composite material is between 20% and 55%, based on the mass of the composite material. Exemplarily, the mass percentage of silicon in the silicon-carbon composite material can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, or a range consisting of any two of the above values. By controlling the mass percentage of silicon in the silicon-carbon composite material within the range of this application, the volume expansion of the silicon-carbon composite material can be reduced, the cycle performance of the secondary battery can be improved, and the secondary battery can have a higher energy density.

[0047] In this application, the carbon content in the silicon-carbon composite material is 45% to 80% by mass.

[0048] In this application, the silicon and carbon contents are calculated after excluding impurity elements in the silicon-carbon composite material, wherein the content of impurity elements is typically less than 0.5%. This application does not limit the aforementioned impurity elements; for example, impurity elements may include, but are not limited to, at least one of oxygen, nitrogen, sulfur, iron, nickel, or aluminum.

[0049] In one embodiment of this application, the pore volume of the porous support carbon material is 0.8 cm³. 3 / g to 1.1cm 3 / g. For example, the pore volume of the porous carrier carbon material can be 0.8 cm³. 3 / g, 0.82cm 3 / g, 0.84cm 3 / g, 0.86cm 3 / g, 0.88cm 3 / g, 0.9cm 3 / g, 0.92cm 3 / g, 0.94cm 3 / g, 0.96cm 3 / g, 0.98cm 3 / g, 1cm 3 / g, 1.02cm 3 / g, 1.04cm 3 / g, 1.06cm 3 / g, 1.08cm 3 / g, 1.1cm 3 / g or a range consisting of any two of the above values. The porous carbon support material includes macropores, mesopores, and micropores. Based on the pore volume of the porous carbon support material, the proportion of micropore volume is ≥80%. Exemplarily, the proportion of micropore volume can be 80%, 82%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, or a range consisting of any two of the above values. In one embodiment of this application, the proportion of micropore volume is ≥90%. In this application, the proportion of micropore volume can be 100%, meaning the porous carbon support material can consist only of micropores. By controlling the pore volume of the porous carbon support material and the proportion of micropore volume within the scope of this application, the pores of the porous carbon support material can provide sufficient buffer space for the expansion of the silicon material, thereby making the silicon-carbon composite material less prone to expansion and further improving the cycle performance of the secondary battery.

[0050] In this application, macropores refer to pores with a diameter greater than 50 nm, mesopores refer to pores with a diameter between 2 nm and 50 nm, and micropores refer to pores with a diameter less than 2 nm.

[0051] This application does not impose any particular limitation on the proportion of the pore volume of the large holes, as long as the purpose of this application can be achieved. For example, the proportion of the pore volume of the large holes can be 0% to 5%. This application does not impose any particular limitation on the proportion of the pore volume of the medium holes, as long as the purpose of this application can be achieved. For example, the proportion of the pore volume of the medium holes can be 0% to 10%.

[0052] In one embodiment of this application, the Dv50 of the silicon-carbon composite material is from 4 μm to 8 μm. Exemplarily, the Dv50 of the silicon-carbon composite material can be 4 μm, 4.2 μm, 4.4 μm, 4.6 μm, 4.8 μm, 5 μm, 5.2 μm, 5.4 μm, 5.6 μm, 5.8 μm, 6 μm, 6.2 μm, 6.4 μm, 6.6 μm, 6.8 μm, 7 μm, 7.2 μm, 7.4 μm, 7.6 μm, 7.8 μm, 8 μm, or a range consisting of any two of the above values. By adjusting the Dv50 value within the range of this application, the compaction density of the negative electrode material layer can be improved, which is beneficial for increasing the energy density of the secondary battery.

[0053] In one embodiment of this application, the Dv99 of the silicon-carbon composite material is 16 μm to 25 μm. Exemplarily, the Dv99 of the silicon-carbon composite material can be 16 μm, 16.2 μm, 16.4 μm, 16.6 μm, 16.8 μm, 17 μm, 17.2 μm, 17.4 μm, 17.6 μm, 17.8 μm, 18 μm, 18.2 μm, 18.4 μm, 18.6 μm, 18.8 μm, 19 μm, 19.2 μm, 19.4 μm, 19.6 μm, 19.8 μm, 20 μm, 20.2 μm, or 20.4 μm. The values ​​are 20.6 μm, 20.8 μm, 21 μm, 21.2 μm, 21.4 μm, 21.6 μm, 21.8 μm, 22 μm, 22.2 μm, 22.4 μm, 22.6 μm, 22.8 μm, 23 μm, 23.2 μm, 23.4 μm, 23.6 μm, 23.8 μm, 24 μm, 24.2 μm, 24.4 μm, 24.6 μm, 24.8 μm, 25 μm, or any two of the above values. By adjusting the value of Dv99 within the range of this application, not only can the structural stability of the silicon-carbon composite material be improved, but also the specific surface area of ​​the silicon-carbon composite material can be reduced, thereby improving the cycle performance and kinetic performance of the secondary battery.

[0054] In one embodiment of this application, the Dn10 of the silicon-carbon composite material is from 0.5 μm to 3 μm. Exemplarily, the Dn10 of the silicon-carbon composite material can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3 μm, or a range consisting of any two of the above values. By adjusting the Dn10 value within the range of this application, the transport distance of lithium ions or electrons in the silicon-carbon composite material particles can be controlled, thereby balancing the electrolyte consumption and kinetic performance of the negative electrode.

[0055] In this application, Dv50 indicates that 50% of the total sample volume has a particle diameter greater than this value, and another 50% of the total sample volume has a particle diameter smaller than this value. Dv99 indicates that 90% of the total sample volume has a particle diameter smaller than this value. Dn10 indicates that 10% of the total sample particles have a particle diameter smaller than this value.

[0056] In one embodiment of this application, the specific surface area of ​​the silicon-carbon composite material is 0.5 m². 2 / g to 8m 2 / g. For example, the specific surface area of ​​the silicon-carbon composite material can be 0.5m².2 / g, 0.7m 2 / g, 0.9m 2 / g, 1m 2 / g, 1.3m 2 / g, 1.5m 2 / g, 1.7m 2 / g, 1.9m 2 / g、2m 2 / g, 2.3m 2 / g, 2.5m 2 / g, 2.7m 2 / g, 2.9m 2 / g、3m 2 / g、3.3m 2 / g, 3.5m 2 / g, 3.7m 2 / g, 3.9m 2 / g、4m 2 / g, 4.3m 2 / g, 4.5m 2 / g, 4.7m 2 / g, 4.9m 2 / g、5m 2 / g, 5.3m 2 / g, 5.5m 2 / g, 5.7m 2 / g, 5.9m 2 / g、6m 2 / g、6.3m 2 / g, 6.5m 2 / g, 6.7m 2 / g, 6.9m 2 / g、7m 2 / g, 7.3m 2 / g, 7.5m 2 / g, 7.7m 2 / g, 7.9m 2 / g、8m 2 / g or a range consisting of any two of the above values. By adjusting the specific surface area of ​​the silicon-carbon composite material within the scope of this application, the contact area between the silicon-carbon composite material and the electrolyte can be controlled, thereby improving the kinetic performance of the secondary battery.

[0057] In this application, the mass percentage of silicon in the silicon-carbon composite material can be controlled by adjusting the time of introducing the first gas. For example, with other preparation conditions remaining unchanged, extending the time of introducing the first gas increases the mass percentage of silicon; shortening the time of introducing the first gas decreases the mass percentage of silicon.

[0058] In this application, the I content can be controlled by adjusting the mass percentage of silicon in the silicon-carbon composite material. Si / I D and I Si / I G The value of I. For example, with other conditions remaining constant, as the mass percentage of silicon increases, I Si / I D As the value of I increases, Si / I G The value increases; the mass percentage of silicon decreases, I Si / I D The value of I decreases. Si / I G The value decreases.

[0059] In this application, the Dv50, Dv99, and Dn10 of the porous carbon support material can be controlled by first classifying, shaping, and sieving the porous carbon support material, thereby controlling the Dv50, Dv99, and Dn10 of the silicon-carbon composite material. For example, the Dv50, Dv99, and Dn10 of the porous carbon support material can be controlled by adjusting the feeding rate during the classification process.

[0060] In this application, the specific surface area of ​​silicon-carbon composite material particles can be controlled by adjusting the duration of the second gas introduction. For example, extending the introduction time of the second gas decreases the specific surface area; shortening the introduction time increases the specific surface area.

[0061] A third aspect of this application provides a secondary battery comprising a positive electrode, a negative electrode, and a separator. The negative electrode includes a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector. The negative electrode material layer comprises the negative electrode material described in any of the foregoing embodiments. Therefore, the secondary battery provided by this application has better cycle performance.

[0062] In this application, the negative electrode sheet includes a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector. The aforementioned "negative electrode material layer disposed on at least one surface of the negative current collector" means that the negative electrode material layer can be disposed on one surface of the negative current collector along its thickness direction, or on two surfaces of the negative current collector along its thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the negative current collector, or only a portion of the surface area; this application has no particular limitation, as long as the purpose of this application is achieved. The negative electrode material layer in this application may also include other negative electrode materials, which may include natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, and SiO2. x(0.5 < x < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, lithium titanate Li4Ti5O with spinel structure 12 and at least one of Li-Al alloy and metallic lithium, etc. In this application, the negative electrode active material includes the negative electrode material and other negative electrode materials. The mixed specific capacity of the negative electrode active material is 400 mAh / g to 600 mAh / g. Based on the total mass of the negative electrode material and other negative electrode materials, the mass ratio of the negative electrode material to other negative electrode materials is (2:98) to (30:70). The negative electrode material layer in this application further includes a binder and a conductive agent. There is no particular limitation on the types of the binder and the conductive agent in this application, as long as the purpose of this application can be achieved. For example, the binder can include at least one of polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, styrene-butadiene copolymer (styrene-butadiene rubber), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, lithium carboxymethyl cellulose, lithium polyacrylate, sodium hydroxymethyl cellulose or potassium hydroxymethyl cellulose, and the conductive agent can include at least one of acetylene black, conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fiber, flake graphite, Ketjen black or graphene, etc. There is no particular limitation on the mass ratio of the negative electrode active material, the binder and the conductive agent in the negative electrode material layer in this application, and those skilled in the art can select according to actual needs as long as the purpose of this application can be achieved.

[0063] There is no particular limitation on the negative electrode current collector in this application, as long as the purpose of this application can be achieved. For example, it can include but is not limited to copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or composite current collector, etc. There is no particular limitation on the thickness of the negative electrode current collector and the negative electrode material layer in this application, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 6 μm to 20 μm, and the thickness of the negative electrode material layer is 20 μm to 120 μm. There is no particular limitation on the thickness of the negative electrode plate in this application, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode plate is 50 μm to 250 μm. In this application, the negative electrode plate may further include a conductive layer, and the conductive layer is located between the negative electrode current collector and the negative electrode material layer. There is no particular limitation on the composition of the above conductive layer, and it can be a commonly used conductive layer in the art. The above conductive layer includes a conductive agent and a binder. There is no particular limitation on the mass ratio of the conductive agent and the binder in the conductive layer in this application, as long as the purpose of this application can be achieved.

[0064] In this application, the positive electrode includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The phrase "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the positive current collector, or only a portion of the surface area; this application has no particular limitation, as long as the purpose of this application is achieved. This application also has no particular limitation on the positive current collector, as long as the purpose of this application is achieved; for example, it can include aluminum foil, aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector). The positive electrode material layer includes a positive electrode active material, which may include at least one of lithium nickel cobalt manganese oxide (e.g., common NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. The positive electrode material layer also includes a conductive agent and a binder. This application does not impose any particular limitation on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, the binder may include at least one of the aforementioned binders, and the conductive agent may include at least one of the aforementioned conductive agents. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved. This application does not impose any particular limitation on the thickness of the positive electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the positive electrode current collector may be 6 μm to 20 μm. This application does not impose any particular limitation on the thickness of the positive electrode material layer, as long as the purpose of this application is achieved. For example, the thickness of the positive electrode material layer can be from 30 μm to 250 μm. This application also does not impose any particular limitation on the thickness of the positive electrode sheet, as long as the purpose of this application is achieved. For example, the thickness of the positive electrode sheet can be from 50 μm to 250 μm. In this application, the positive electrode sheet may further include a conductive layer, which is located between the positive electrode current collector and the positive electrode material layer. This application does not impose any particular limitation on the composition of the aforementioned conductive layer, and it can be a conductive layer commonly used in the art. The aforementioned conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the mass ratio of the conductive agent to the binder in the conductive layer, as long as the purpose of this application is achieved.

[0065] In this application, a separator is used to separate the positive and negative electrode plates, prevent internal short circuits in the secondary battery, allow electrolyte ions to pass freely, and does not affect the electrochemical charging and discharging process. This application does not impose any particular limitations on the separator, as long as it achieves the purpose of this application. For example, the material of the separator may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid; the type of separator may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0066] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. For example, the inorganic layer includes inorganic particles and a binder. This application does not have particular limitations on the inorganic particles, and may include at least one of alumina, 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, or barium sulfate. This application does not have particular limitations on the binder, and may include at least one of the above-mentioned binders. The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0067] In this application, the secondary battery further includes an electrolyte, which comprises a lithium salt and a non-aqueous solvent. The lithium salt may include various lithium salts commonly used in the art, such as at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. This application does not impose any particular limitation on the concentration of the lithium salt in the electrolyte, as long as it achieves the purpose of this application. This application also does not impose any particular limitation on the non-aqueous solvent, as long as it achieves the purpose of this application; for example, it may include, but is not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (EMC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). Fluorinated carbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 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 aforementioned carboxylic acid ester compounds may include, but are 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, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The aforementioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0068] The secondary battery of this application also includes a packaging bag for containing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the art for secondary batteries. This application does not limit the aforementioned other components. This application does not have any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0069] The secondary battery described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In some embodiments, the secondary battery may include, but is not limited to, a lithium metal secondary battery, a lithium-ion secondary battery (lithium-ion battery), a lithium polymer secondary battery, or a lithium-ion polymer secondary battery.

[0070] The preparation process of the secondary battery described in this application is well known to those skilled in the art, and this application has no particular limitations. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it; and then allowing it to stand, form, degas, and trim the edges to obtain the secondary battery; or, stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it; and then allowing it to stand, form, degas, and trim the edges to obtain the secondary battery. In addition, overcurrent protection components, conductive plates, etc., may be placed in the packaging bag as needed to prevent the internal pressure of the secondary battery from rising and overcharging / discharging.

[0071] In this application, the formation process is as follows:

[0072] (1) 0.5C constant current charging, cutoff time 8000s, voltage limit 4.5V; (2) 4.5V constant voltage charging, cutoff current 0.1C, time limit 8000s; (3) 0.5C constant current discharging, cutoff voltage 3.0V, time limit 8000s; (4) 0.1C constant current discharging, cutoff voltage 3.0V, time limit 8000s; (5) 0.5C constant current charging, cutoff voltage 3.85V, time limit 8000s; (6) 3.85V constant voltage charging, cutoff current 0.05C, time limit 8000s.

[0073] In this application, the compaction density of the negative electrode material layer after formation is 1.39 g / cm³. 3 Up to 1.46 g / cm 3 .

[0074] A fourth aspect of this application provides an electronic device that includes a secondary battery as described in any of the foregoing embodiments. Therefore, the electronic device provided by this application has good performance characteristics.

[0075] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, etc.

[0076] Example

[0077] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0078] Test methods and equipment:

[0079] Loop testing:

[0080] Place the lithium-ion battery in a 25°C constant temperature test chamber and let it stand for 30 minutes to allow it to reach a constant temperature of 25°C. Charge it at a constant current of 0.7C to 4.5V, then charge it at a constant voltage to 0.025C. Let it stand for 5 minutes, then discharge it at a constant current of 0.5C to 3.0V. Record the initial discharge capacity as C0. Repeat this process 500 times and record the discharge capacity after 500 cycles as C1.

[0081] After 500 cycles, the capacity retention rate is calculated as C1 / C0 × 100%.

[0082] Take a lithium-ion battery that has been charged to 3.85V and measure its thickness at this point as the initial thickness T0. Repeat the above cyclic testing steps for 500 cycles to bring the lithium-ion battery to a fully charged state of 4.5V. Measure the thickness of the lithium-ion battery at this point using a micrometer; this thickness is T1.

[0083] After 500 cycles, the thickness expansion rate is calculated as (T1-T0) / T0 × 100%.

[0084] Negative electrode material layer compaction density test:

[0085] The thickness of the cold-pressed negative electrode sheet was measured using a micrometer. The average thickness (h1) of the thickness measurements at 12 different locations was calculated. A circular cutter was then used to punch out an area of ​​1540.25 mm² from the cold-pressed negative electrode sheet. 2The circular sheet was weighed on a balance with a resolution of 1 / 10,000. The punching / weighing process was repeated 5 times, and the average weight was taken to obtain the weight m1 of the circular sheet. Pure copper foil was then taken and its thickness h2 and area of ​​1540.25 mm² were obtained using the same method. 2 The weight of a round piece of pure copper foil is m2.

[0086] The compaction density of the cold-pressed negative electrode material layer is Q0 = (m1-m2) / (h1-h2) / 1540.25.

[0087] A lithium-ion battery charged to 3.85V was disassembled to obtain the negative electrode sheet. The thickness of the negative electrode sheet was measured using a micrometer at 12 different locations, and the average thickness (h3) was calculated. A circular cutter was used to punch out an area of ​​1540.25 mm² from the formed negative electrode sheet. 2 The circular sheet was weighed on a balance with a resolution of 1 / 10,000. The punching / weighing process was repeated 5 times, and the average weight was taken to obtain the weight m3 of the circular sheet. Pure copper foil was then taken and its thickness h2 and area of ​​1540.25 mm² were obtained using the same method. 2 The weight of a round piece of pure copper foil is m2.

[0088] The compaction density of the negative electrode material layer after formation is Q1 = (m3-m2) / (h3-h2) / 1540.25.

[0089] Silicon mass percentage test:

[0090] Weigh 0.1g of silicon-carbon composite material into a polytetrafluoroethylene (PTFE) beaker, add 10mL of nitric acid, and heat to digest. Add another 10mL of nitric acid, and repeat the digestion process once more. After cooling, filter the digested solution to remove the residue, and dilute to 100mL in a volumetric flask. Add the prepared solution to a nebulizer and perform testing using inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0091] Raman test:

[0092] Place 0.5g of silicon-carbon composite material in the center of the sample cell, ensuring the sample volume is less than 50% of the cell's capacity, and flatten it with a glass slide. Place the sample cell on the microscope stage, turn on the white light source, focus the sample using a 10X objective lens, and perform testing using a 532nm laser source. Set the testing range to 150cm. -1 Up to 3500cm -1 Turn off indoor light sources and collect the full spectrum.

[0093] Specific surface area and pore volume testing:

[0094] The specific surface area, pore volume, and micropore volume of silicon-carbon composite materials were tested using a fully automated specific surface area and porosity analyzer (model ASAP2020 HD88) via nitrogen adsorption method.

[0095] Particle size test:

[0096] The particle size distribution of the silicon-carbon composite material was determined using laser diffraction. First, 0.2 g of the silicon-carbon composite material was added to a 50 mL beaker, followed by two drops of 1 wt% polyethoxynonylphenol surfactant. After gentle shaking, 20 mL of water was added. The sample dispersion was obtained by ultrasonic dispersion for 5 min using a 120 W ultrasonic cleaner. The particle size distribution was then measured using a MasterSizer 2000 laser particle size analyzer to obtain the particle sizes Dv50, Dv99, and Dn10.

[0097] Capacity test:

[0098] Silicon-carbon composite material, conductive agent (SP), binder (SBR), carbon nanotubes (CNTs), and dispersant (CMC) were mixed in a mass ratio of 84:10:5:0.4:0.6, and deionized water was added to obtain a negative electrode slurry with a solid content of 48 wt%. After the negative electrode slurry was mixed evenly, it was coated onto copper foil, and after drying, cold pressing, and stamping, a negative electrode sheet was obtained.

[0099] In a glove box where the water and oxygen content are both less than 10 ppm, ethyl methyl carbonate (EMC), ethylene carbonate (EC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain a mixed solvent. Then, fluoroethylene carbonate (FEC) at a volume fraction of 10% of the mixed solvent is added, and finally, lithium salt LiPF6 is added to obtain the electrolyte. The concentration of lithium salt LiPF6 is 1 mol / L.

[0100] In a glove box where the water and oxygen content are both less than 10 ppm, the above-mentioned negative electrode sheet, counter electrode lithium metal sheet, polypropylene (PP) separator and electrolyte are assembled into a button cell.

[0101] Specific capacity test: After the above button battery was left to stand for 6 hours at 25℃, it was discharged to 5mV at a current of 0.05C, then discharged to 5mV at a current of 50μA, left to stand for 5 minutes, then discharged to 5mV at a current of 10μA, left to stand for 5 minutes, and then charged to 2.0V at a rate of 0.05C. The above discharge capacity is recorded as G0, and the charge capacity is recorded as G1.

[0102] The specific capacity of silicon-carbon composite materials = G1;

[0103] The initial coulombic efficiency of silicon-carbon composite materials = G1 / G0 × 100%.

[0104] Example 1

[0105] <Preparation of Negative Electrode Sheets>

[0106] 1000g of coconut shell carbon was added to a fluidized bed equipped with a stirrer, and the stirring speed was controlled at 200rpm. Nitrogen gas was introduced at a flow rate of 10L / min to achieve a fluidized state, and the fluidized bed was heated to T1 = 500℃. After the temperature stabilized, a silane / argon mixture with a flow rate L1 of 4L / min and a volume concentration of 50% was introduced for a time t1 of 140min. The outlet valve was adjusted to maintain a furnace pressure P1 of 80kPa, resulting in a porous carbon material as a carrier for silicon deposition. Subsequently, an acetylene / argon mixture with a flow rate L2 of 6L / min and a volume concentration of 50% was introduced for a time t2 of 300min. The outlet valve was adjusted to maintain a furnace pressure P2 of 10kPa, resulting in a carbon material coating on the surface of the porous carbon material as a carrier for silicon deposition. After the acetylene is introduced, heating is stopped, and nitrogen is introduced at a rate of 4 L / min until the temperature of the fluidized bed furnace drops to 45°C. Then heating and stirring are stopped, and the prepared silicon-carbon composite material is taken out for use.

[0107] The flow rate L1, time t1, pressure P1 in the sealed cavity, flow rate L2, time t2, and pressure P2 of the second gas are shown in Table 1; the I of the silicon-carbon composite material Si / I D I Si / I G Silicon mass percentage W Si Table 2 shows the specific surface area, specific capacity, initial coulombic efficiency, and the pore volume R0 and micropore volume ratio R1 of the porous carbon support material, Dv50, Dv99, Dn10.

[0108] A negative electrode active material (a mixture of silicon-carbon composite material and artificial graphite at a mass ratio of 1:9, with a mixed specific capacity of 480 mAh / g), carbon nanotubes, lithium carboxymethyl cellulose, and lithium polyacrylate at a mass ratio of 97.4:0.2:0.4:2 was mixed with deionized water as solvent, and a negative electrode slurry was obtained under vacuum stirring. The solid content of the negative electrode slurry was 45 wt%, and the viscosity was 6000 mPa·s. The negative electrode slurry was uniformly coated onto one surface of a 10 μm thick copper foil current collector, and the copper foil was dried at 80 °C, resulting in a coating weight of 100.1 mg / 1540.25 mm. 2A negative electrode sheet with a negative electrode material layer coated on one side is obtained. The above steps are then repeated on the other surface of the copper foil to obtain a negative electrode sheet with a negative electrode material layer coated on both sides. After cold pressing, cutting, and slitting, a negative electrode sheet with a size of 661mm × 78mm is obtained. The compaction density Q0 of the negative electrode material layer after cold pressing is shown in Table 2.

[0109] <Preparation of the positive electrode>

[0110] LiCoO2 (positive electrode active material), conductive carbon black (conductive agent), and polyvinylidene fluoride (PVDF) (binder) were mixed in a mass ratio of 96.7:1.7:1.6. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum to obtain a positive electrode slurry with a solid content of 76 wt%. The positive electrode slurry was uniformly coated onto one surface of a 9 μm thick aluminum foil used as a positive electrode current collector. The aluminum foil was dried at 120 °C, resulting in a coating weight of 260 mg / 1540.25 mm. 2 A positive electrode sheet with a positive electrode material layer coated on one side is obtained. Then, the above steps are repeated on the other side of the aluminum foil to obtain a positive electrode sheet with a positive electrode material layer coated on both sides. After cold pressing, cutting, and slitting, a positive electrode sheet with a size of 661mm×76.5mm is obtained.

[0111] <Preparation of Electrolyte>

[0112] In an argon-atmospheric glove box with a water content of less than 10 ppm, FEC, EC, PC, EMC, and DEC were mixed in a mass ratio of 5:10:15:20:50 to obtain an organic solvent. Lithium salt LiPF6 was then added to the organic solvent to obtain the electrolyte. The lithium salt LiPF6 comprised 12.5% ​​by mass, with the remainder being the organic solvent.

[0113] <Isolation membrane>

[0114] A porous polyethylene film with a thickness of 10 μm (supplied by Celgard) was used.

[0115] <Preparation of Lithium-ion Batteries>

[0116] The positive electrode, separator, and negative electrode prepared above are stacked in sequence, with the separator positioned between the positive and negative electrode to provide isolation. The electrode assembly is then wound to obtain the electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, degassing, and edge trimming, a lithium-ion battery is obtained.

[0117] The formation process consists of the following steps: (1) 0.5C constant current charging, cutoff time 8000s, voltage limit 4.5V; (2) 4.5V constant voltage charging, cutoff current 0.1C, time limit 8000s; (3) 0.5C constant current discharging, cutoff voltage 3.0V, time limit 8000s; (4) 0.1C constant current discharging, cutoff voltage 3.0V, time limit 8000s; (5) 0.5C constant current charging, cutoff voltage 3.85V, time limit 8000s; (6) 3.85V constant voltage charging, cutoff current 0.05C, time limit 8000s.

[0118] The compaction density Q1 of the anode material layer after formation is shown in Table 2.

[0119] Examples 2 to 20

[0120] Except for adjusting the relevant preparation parameters according to Table 1 in the <Preparation of Negative Electrode Sheet>, the rest is the same as in Example 1.

[0121] In particular, due to the changes in the preparation parameters in the above embodiments, the specific capacity of the silicon-carbon composite material changes. By adjusting the mass ratio of silicon-carbon composite material to artificial graphite, the mixed specific capacity of the negative electrode active material in each embodiment is 480 mAh / g.

[0122] Comparative Examples 1 to 8

[0123] Except for adjusting the relevant preparation parameters according to Table 1 in the <Preparation of Negative Electrode Sheet>, the rest is the same as in Example 1.

[0124] Among them, the specific capacity of silicon-carbon composite materials varied due to the changes in preparation parameters in each of the above comparative examples. By adjusting the mass ratio of silicon-carbon composite materials to artificial graphite, the mixed specific capacity of the negative electrode active materials in each comparative example was 480 mAh / g.

[0125] The preparation parameters, powder performance parameters, and electrical performance parameters of each embodiment and comparative example are shown in Tables 1 and 2.

[0126] Table 1

[0127]

[0128]

[0129] Table 2

[0130]

[0131]

[0132] As can be seen from Examples 1 to 20 and Comparative Examples 1 to 8, when the negative electrode material is prepared using the preparation method of this application, and all preparation parameters are within the scope of this application, and when the above negative electrode material is used to prepare a lithium-ion battery, the lithium-ion battery has a higher capacity retention rate after 500 cycles and a lower thickness expansion rate. This shows that when the negative electrode material is prepared using the preparation method of this application, and all preparation parameters are within the scope of this application, and when the above negative electrode material is applied to a lithium-ion battery, the cycle performance of the lithium-ion battery can be improved.

[0133] As can be seen from Examples 1 to 3, the pressure of the sealed cavity after the first gas is introduced is 80 kPa. By controlling the introduction time of silane, the mass percentage of silicon in the silicon-carbon composite material is adjusted to 24.8% to 35.3%. As the silicon content increases, I Si / I D and I Si / I G The silicon content gradually increases because as the silicon content increases, the silicon content inside and on the surface of the porous carrier also increases synchronously, leading to an enhancement of the characteristic signal peak intensity of silicon in the Raman spectrum, which in turn leads to I... Si / I D and I Si / I G The lithium-ion batteries in Examples 1 to 3 exhibit high capacity retention after 500 cycles and low thickness expansion, demonstrating good cycle performance. However, with increasing silicon content, the capacity retention after 500 cycles gradually decreases, while the thickness expansion gradually increases. This is because the increased silicon content in the silicon-carbon composite particles leads to an increase in the number of lithium intercalations per particle, resulting in particle volume expansion and an increase in the number of internal microcracks, thus affecting the cycle performance of the lithium-ion battery.

[0134] As can be seen from Examples 4 to 9, the carbon coating amount in Examples 7, 8, and 9 is increased compared to Examples 4, 5, and 6, respectively. This leads to an increase in the thickness of the carbon material layer on the particle surface, resulting in a weakening of the silicon peak signal intensity during Raman testing. Therefore, the Ig of Examples 7, 8, and 9 is reduced. Si / I D and I Si / I G Compared to Examples 4, 5, and 6, I Si / I D and I Si / I GThe silicon content in Examples 7, 8, and 9 is lower than that in Examples 4, 5, and 6, respectively. Therefore, the specific capacity of Examples 7, 8, and 9 is lower than that of Examples 4, 5, and 6, respectively. Furthermore, the lithium-ion batteries in Examples 4 to 9 exhibit higher capacity retention after 500 cycles and lower thickness expansion, demonstrating better cycle performance. The lower silicon content in Examples 7, 8, and 9 further improves the contact between the silicon material on the particle surface and the electrolyte, thereby reducing the thickness increase of the solid electrolyte interphase (SEI) film and the consumption of active lithium caused by electrolyte side reactions. Therefore, Examples 7, 8, and 9 exhibit better cycle performance than Examples 4, 5, and 6.

[0135] As can be seen from Examples 7 to 9 and Comparative Examples 1 to 3, the pressure of the sealed cavity after the first gas was introduced in Examples 7 to 9 was 80 kPa. This high reaction pressure increases the speed and quantity of silicon source molecules entering the porous support, thus facilitating pyrolysis deposition of silicon source molecules within the pores of the porous support and effectively preventing the decomposition and deposition of silicon source gas on the outer surface of the porous support. In contrast, the pressure of the sealed cavity after the first gas was introduced in Comparative Examples 1 to 3 was 10 kPa. Some silicon source molecules would pyrolyze and deposit on the particle surface before entering the pores of the porous support, resulting in a stronger silicon peak signal in the Raman spectrum. Therefore, the I peak signal in Comparative Examples 1 to 3 was... Si / I D and I Si / I G Each is higher than I in Examples 7 to 9. Si / I D and I Si / I G .

[0136] Since most of the silicon in Examples 7 to 9 expands within the pores of the particles, the remaining space in the pore walls and pores of the porous carrier absorbs this expansion. However, in Comparative Examples 1 to 3, the silicon content on the outer surface of the particles is higher. The lithium insertion and expansion of this silicon directly compresses the surrounding active material particles, leading to an increase in the thickness of the negative electrode material layer. Therefore, the thickness expansion rate of the lithium-ion batteries in Comparative Examples 1 to 3 after 500 cycles is greater than that in Examples 7 to 9. The repeated expansion and contraction of the silicon on the outer surface of the particles in Comparative Examples 1 to 3 during lithium insertion / extraction gradually pulverizes and consumes a large amount of electrolyte, resulting in a decrease in cycle performance. Therefore, the capacity retention rate of the lithium-ion batteries in Comparative Examples 1 to 3 after 500 cycles is lower than that in Examples 7 to 9. Thus, the cycle stability of the lithium-ion batteries in Comparative Examples 1 to 3 is worse than that of the lithium-ion batteries in Examples 7 to 9.

[0137] As shown in Table 2, the compaction density of the cold-pressed negative electrode material layers in Examples 1 to 20 ranges from 1.75 g / cm³. 3 Up to 1.76 g / cm 3 This is because the mixed specific capacity of the negative electrode active material is 480 mAh / g, the coating weight on the copper foil surface is the same, and the thickness of the negative electrode sheet is controlled by the cold pressing process. The combined effect of these three factors results in a compaction density range of 1.75 g / cm³ for the negative electrode material layer after cold pressing. 3 Up to 1.76 g / cm 3 .

[0138] As can be seen from Examples 1 to 3, the compaction density of the formed negative electrode material layer is 1.45 g / cm³. 3 Up to 1.46 g / cm 3 This is because silicon in the particles is not enriched on the particle surface, and the volume change after lithium intercalation and expansion occurs inside the pores of the particles, and is not reflected in the thickness expansion of the negative electrode sheet. In contrast, the compaction density of the negative electrode material layers after formation in Comparative Examples 1 to 3 is 1.3 g / cm³. 3 Up to 1.4 g / cm 3 Furthermore, the compaction density decreased with the increase of silicon content, indicating that its thickness expansion was significantly higher than that of Examples 1 to 3. This is because silicon in Comparative Examples 1 to 3 was enriched on the particle surface, and the volume change after silicon lithium intercalation was directly transmitted to the negative electrode material layer, resulting in a larger volume expansion and lower compaction density of the negative electrode material layer.

[0139] Depend on Figure 1 It can be seen that the Raman spectrum of the silicon-carbon composite material in Example 7 is at 476±8 cm⁻¹. -1 There is a characteristic peak of amorphous silicon at 1360±20 cm⁻¹. -1 The characteristic D band peak of carbon is located at 1580±20 cm⁻¹. -1 The characteristic G-band peak of carbon is present. Additionally, the intensity I of the characteristic peak of amorphous silicon in Example 7 is... Si The intensity I of the amorphous silicon characteristic peak is lower than that of Comparative Example 1 Si The intensity of the characteristic peak I of the D band of carbon in Example 7 D The intensity I of the D band characteristic peak of carbon in Comparative Example 1 is higher than that of the carbon in Comparative Example D The intensity of the characteristic peak I of the G band of carbon in Example 7 G The intensity I of the G-band characteristic peak of carbon in Comparative Example 1 is higher than that of the carbon in Comparative Example G The silicon-carbon composite material in Example 7 has I Si / I D 0.32, I Si / I G It is 0.4, while I in Comparative Example 1 is 0.4. Si / ID 1.04, I Si / I G The value is 1.32, thus the I of the silicon-carbon composite material in Example 7 is... Si / I D I Si / I G I is less than that of the silicon-carbon composite material in Comparative Example 1 Si / I D I Si / I G .

[0140] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0141] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0142] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for preparing a negative electrode material, comprising the following steps: (1) The porous carrier carbon material is placed in a sealed cavity for heat treatment. The heat treatment temperature is the temperature T1 of silicon source thermal decomposition, and T1 is 400℃ to 600℃. (2) A porous carrier carbon material containing the silicon source is deposited by introducing a first gas to obtain a silicon material, wherein the flow rate L1 of the first gas is 3L / min to 5L / min, the time t1 is 140min to 450min, and the pressure P1 in the sealed cavity is 70KPa to 90KPa. (3) Then a second gas containing a carbon source is introduced to react and obtain the negative electrode material, wherein the flow rate L2 of the second gas is 5 L / min to 7 L / min, the time t2 is 300 min to 480 min, and the pressure P2 in the sealed cavity is 5 kPa to 20 kPa. The porous carbon support material has a pore volume of 0.8 cm³. 3 / g to 1cm 3 / g, the porous carrier carbon material includes macropores, mesopores and micropores, and based on the pore volume of the porous carrier carbon material, the proportion of the micropore volume is ≥82.5%; The silicon content in the negative electrode material is 24% to 45% by mass. The negative electrode material satisfies the following conditions: Dv50 is 4μm to 7μm, Dv99 is 16μm to 20μm, and Dn10 is 0.5μm to 2.5μm. The Raman spectrum of the negative electrode material is at 476±8 cm⁻¹. -1 There is a characteristic peak of amorphous silicon at 1360±20 cm⁻¹. -1 The characteristic D band peak of carbon is located at 1580±20 cm⁻¹. -1 The amorphous silicon has a carbon G-band characteristic peak at a certain location, and the intensity I of the characteristic peak is... Si The intensity I of the characteristic peak of the D band of the carbon D The ratio I Si / I D The value ranges from 0.15 to 0.

35. The intensity I of the amorphous silicon characteristic peak Si The intensity I of the characteristic peak of the G band of the carbon G The ratio I Si / I G It ranges from 0.2 to 0.

4.

2. The preparation method according to claim 1, wherein, The porous carrier carbon material includes at least one of biomass-derived carbon, resin-derived carbon, petroleum coke-derived carbon, coal-derived carbon, metal-modified carbon material, or metal oxide-modified carbon material. The metal includes at least one of Fe, Co, Pd, Zn or Al; The resin-derived carbon includes at least one of phenolic resin carbon, polyethylene carbon, or epoxy resin carbon.

3. The preparation method according to claim 1, wherein, The silicon source includes at least one of silane, ethane, or propane.

4. The preparation method according to claim 1, wherein, The carbon source includes at least one of acetylene, ethylene, propylene, propane, or methane.

5. The preparation method according to claim 1, wherein it satisfies at least one of the following characteristics: (1) The first gas further includes an inert gas, and the volume percentage of the silicon source is 40% to 60% based on the volume of the first gas; (2) The second gas also includes an inert gas, and the carbon source has a volume percentage of 40% to 60% based on the volume of the second gas.

6. A negative electrode material prepared by the method according to any one of claims 1 to 5, wherein, The negative electrode material is a silicon-carbon composite material, which includes a porous carrier carbon material. Silicon material is disposed within the pores of the porous carrier carbon material, and carbon material is disposed on at least a portion of the surface of the porous carrier carbon material.

7. The negative electrode material according to claim 6, wherein, The specific surface area of ​​the silicon-carbon composite material is 0.5 m². 2 / g to 8m 2 / g.

8. A secondary battery comprising a positive electrode, a negative electrode, and a separator, wherein the negative electrode comprises a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector, the negative electrode material layer comprising the negative electrode material according to any one of claims 6 to 7.

9. An electronic device comprising the secondary battery of claim 8.

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