Silicon-carbon composite material, preparation method thereof, negative plate and lithium ion battery

Abstract

The invention provides a silicon-carbon composite material and a preparation method thereof, a negative plate and a lithium ion battery. The preparation method comprises the following steps: S1, conveying a preheated and gasified silicon source material into a first container containing porous carbon through first carrier gas; the silicon source material has an annular structure; s2, carrying out heat preservation treatment on the first container to obtain a carbon material; the heat preservation treatment time is 4-10 hours; and S3, carrying out carbon coating on the carbon material to obtain the silicon-carbon composite material. According to the preparation method disclosed by the invention, the safety coefficient of a preparation system can be improved through liquid-phase evaporation-vapor deposition, and the safety risk of monosilane used when the silicon-carbon composite material is prepared through traditional chemical vapor deposition is effectively avoided; besides, according to the preparation method disclosed by the invention, through a capillary agglutination phenomenon, the deposition uniformity and depth of silicon can be effectively promoted, so that the electrical properties, including long cycle performance, of the material are further improved.

Description

Technical Field

[0001] The present invention relates to a silicon-carbon composite material, a preparation method thereof, a negative electrode sheet and a lithium-ion battery. Background Art

[0002] Silicon has an extremely high theoretical specific capacity (about 4200 mAh / g) and is a promising next-generation negative electrode material. However, during the charge and discharge process, silicon undergoes a huge volume change (about 300%), which easily causes the electrode material to crack and pulverize, thereby sharply reducing the cycle performance of the battery. To solve this problem, compounding silicon with porous carbon is an effective approach. By depositing silane in porous carbon, a silicon-carbon composite material can be prepared. Porous carbon has a rich pore structure, which can provide a buffer space for the volume expansion of silicon, and at the same time can improve the electrical conductivity and mechanical strength of the electrode. Silane can decompose and deposit on the pores and surface of porous carbon under specific conditions to form nano-scale silicon particles, and these silicon particles are evenly distributed in the porous carbon, effectively alleviating the volume expansion effect of silicon.

[0003] However, conventional vapor deposition often uses silane, which has high requirements for equipment and is accompanied by certain safety risks. Therefore, there is an urgent need to develop a safe and efficient preparation method for silicon-carbon composites, which has high practical significance. Summary of the Invention

[0004] In order to overcome the safety risks existing in the preparation system of the prior art and the defect that the lithium-ion battery further produced from the silicon-carbon composite material prepared by the prior art has low electrical performance, the present application provides a silicon-carbon composite material, a preparation method thereof, a negative electrode sheet and a lithium-ion battery. The preparation method of the present invention can improve the safety factor of the preparation system through liquid-phase evaporation-vapor deposition, effectively avoiding the safety risks existing in the use of silane in the preparation of silicon-carbon composite materials by traditional chemical vapor deposition (CVD); in addition, the preparation method of the present invention can effectively promote the deposition uniformity and depth of silicon through the "capillary condensation" phenomenon, thereby further improving the electrical performance of the material, including having a higher 2V capacity and 2V initial efficiency, as well as long cycle performance. Specifically, the 2V capacity is above 1000 mAh / g, the 2V initial efficiency is above 75%, and the capacity retention rate after 500 cycles is above 74%.

[0005] The present invention provides a preparation method for a silicon-carbon composite material, which comprises the following steps:

[0006] S1. Transport the preheated and vaporized silicon source material to a first container containing porous carbon through a first carrier gas; the silicon source material has a ring structure; the mass ratio of the silicon source material to the porous carbon is (0.6 - 1.65):1; the preheating temperature of the silicon source material is 100 - 250°C;

[0007] S2. Insulate the first container to obtain a carbon material; the temperature of the insulation treatment is 450 °C or higher; the time of the insulation treatment is 4 - 10 h;

[0008] S3. Perform carbon coating on the carbon material to obtain a silicon-carbon composite material.

[0009] In the present invention, during the preparation process of the silicon-carbon composite material, using a silicon source material with a specific chemical structure can improve the utilization rate of silane and the uniformity of silane deposition, thereby improving the product quality.

[0010] In some embodiments, the preparation method of the silicon-carbon composite material is carried out in a negative electrode material preparation device, and the negative electrode material preparation device includes a first preheating chamber, a mixing and heating chamber, a first container, and a vacuum assembly; the outlet of the first preheating chamber is connected to the inlet of the mixing and heating chamber; the first preheating chamber is used to preheat a first carrier gas and a silicon source material; the first container includes a rotary furnace; the inlet of the rotary furnace is connected to the outlet of the mixing and heating chamber; the inlet of the vacuum assembly is connected to the outlet of the rotary furnace.

[0011] In a specific embodiment, the negative electrode material preparation device further includes a second preheating chamber, and the outlet of the second preheating chamber is connected to the inlet of the mixing and heating chamber; the second preheating chamber is used to preheat a second carrier gas.

[0012] In the present invention, a mixing and heating chamber is arranged between the first container and each preheating chamber to facilitate controlling the mixing temperature of each material and avoid the problem of poor experimental stability.

[0013] In a preferred embodiment, the negative electrode material preparation device further includes a control unit; the control unit includes a control center, and a first valve, a second valve, a third valve, a first pressure detection element, a second pressure detection element, and a third pressure detection element respectively electrically connected to the control center; the first pressure detection element and the first valve are both arranged on the connecting pipeline between the first preheating chamber and the mixing and heating chamber; the second pressure detection element and the second valve are arranged on the connecting pipeline between the second preheating chamber and the mixing and heating chamber; the third pressure detection element and the third valve are both arranged on the connecting pipeline between the vacuum assembly and the rotary furnace.

[0014] In a specific embodiment, the rotary furnace includes a furnace tube and a driving mechanism, and the driving mechanism is used to drive the furnace tube to rotate.

[0015] In a preferred embodiment, a plurality of material lifting plates and a material conveying device are provided inside the furnace tube; the material lifting plates are spirally distributed along the furnace tube and are arranged at the inlet end of the furnace tube; the material conveying device is arranged at the outlet end of the furnace tube.

[0016] In a preferred embodiment, rotary joints are provided at both ends of the furnace tube, and each rotary joint is respectively connected to the connecting pipes of the mixing and heating chamber and the rotary furnace, and the connecting pipes of the rotary furnace and the vacuum assembly; further preferably, filter elements are provided at the ends of each rotary joint to allow gas to pass through and intercept solid materials.

[0017] In a specific embodiment, the vacuum assembly includes a vacuum pump, a dust collector, and a filtering element connected in sequence.

[0018] In a specific embodiment, the preparation device for the negative electrode material further includes an exhaust gas emission unit; the exhaust gas emission unit is connected to the outlet of the vacuum assembly; more preferably, the exhaust gas emission unit includes an alkali liquid tank, a buffer tank, a liquid seal tank, and a flame arrester.

[0019] In a preferred embodiment, cooling and temperature control devices are independently provided inside the rotary furnace, the first preheating chamber, the second preheating chamber, and the mixing and heating chamber.

[0020] In a specific embodiment, the control unit further includes a fourth valve and a fourth pressure detection element respectively electrically connected to the control center, and the fourth valve and the fourth pressure detection element are both arranged on the connecting pipeline between the mixing and heating chamber and the rotary furnace; the first valve, the second valve, the third valve, and the fourth valve are all solenoid valves.

[0021] Wherein, a fifth valve may be provided at the inlet of the first preheating chamber for controlling the material entering the first preheating chamber electrically or manually by controlling the fifth valve when ventilation is required.

[0022] Wherein, a sixth valve may be provided at the inlet of the second preheating chamber for controlling the material entering the second preheating chamber electrically or manually by controlling the sixth valve when ventilation is required.

[0023] In the present invention, the high-hermetic vacuum deposition equipment with the above special structure can further increase the driving force for the silicon source material to enter the pores of the porous carbon, greatly improve the deposition rate of silicon, reduce the process time, and improve the equipment utilization rate.

[0024] In the present invention, when the mass ratio of the silicon source material to the porous carbon is less than 0.6, the silicon content in the obtained silicon-carbon composite material is low, resulting in a decrease in the first efficiency and capacity; when the mass ratio of the silicon source material to the porous carbon is higher than 1.65, it leads to an increase in the amount of floating silicon (i.e., the deposition amount of silicon on the surface of the porous carbon) and production safety.

[0025] In some embodiments, in step S1, the mass ratio of the silicon source material to the porous carbon is (0.6 - 1.4):1, preferably (0.8 - 1.1):1, for example 1.1:1.

[0026] In the present invention, the initial state of the silicon source material is liquid and becomes gaseous after preheating.

[0027] In some embodiments, in step S1, the silicon source material includes cyclic liquid silane; the cyclic liquid silane is easily vaporized and turns into gaseous after preheating; the cyclic silane has a higher capillary condensation effect, and the cyclic liquid silane can further improve the safety of the equipment;

[0028] In a specific embodiment, the silicon source material is one or more of cyclopentasilane, cyclobutasilane, cyclohexasilane, and decamethylcyclopentasilane, preferably cyclopentasilane; wherein, the high kinetic diameter and cyclic steric hindrance effect of the cyclopentasilane can effectively prevent the aggregation of deposited silicon in the pores, ensuring that the obtained silicon-carbon composite material has high capacity and high first efficiency.

[0029] In some embodiments, in step S1, the first carrier gas includes nitrogen.

[0030] In some embodiments, in step S1, the conveying gas velocity of the first carrier gas is 500 - 1000 mL / min, for example 500 mL / min.

[0031] In some embodiments, in step S1, the conveying duration of the first carrier gas is 60 - 120 min, preferably 90 - 120 min, for example 90 min.

[0032] In some embodiments, in step S1, after introducing the silicon source material into the first container, the first container is subjected to a cooling treatment; preferably, the temperature of the cooling treatment is 50 - 150 °C, for example 50 °C; preferably, the time of the cooling treatment is 10 - 30 min, for example 15 min.

[0033] In the present invention, through the above cooling treatment, a low-temperature zone is formed in the first container, which is beneficial for the silicon source material to enter the pore structure of the porous carbon; after the conveying of the silicon source material is completed, the first container is heated and kept warm to form a high-temperature zone, so that the silicon source material is completely cracked.

[0034] In some embodiments, the delivery process of the silicon-carbon composite material further includes the following cyclic steps: introducing a second carrier gas into the first container containing porous carbon; then transporting the preheated and vaporized silicon source material to the first container containing porous carbon through a first carrier gas, and performing a cooling treatment on the first container; thereafter, evacuating the first container to a vacuum.

[0035] In a specific embodiment, the second carrier gas includes nitrogen.

[0036] In a specific embodiment, the gas velocity of the second carrier gas is 500 - 1000 mL / min, for example, 500 mL / min.

[0037] In a specific embodiment, the introduction duration of the second carrier gas is 30 - 120 min, for example, 60 min.

[0038] In a preferred embodiment, the number of repetitions of the cyclic step is 3 times.

[0039] In some embodiments, in step S2, before performing the heat preservation treatment on the first container, a heating treatment is performed on the first container, and the temperature of the heating treatment is 150 - 600 °C, preferably 180 - 250 °C.

[0040] In a specific embodiment, the temperature control program of the first container includes the following steps: first heating the first container to 150 - 350 °C for the first heat preservation, and the time of the first heat preservation is 2 - 4 h; then heating the first container to 450 - 600 °C for the second heat preservation, and the time of the second heat preservation is 4 - 8 h.

[0041] In a preferred embodiment, the temperature control program of the first container includes the following steps: first heating the first container to 250 °C for the first heat preservation, and the time of the first heat preservation is 4 h; then heating the first container to 500 °C for the second heat preservation, and the time of the second heat preservation is 6 h; and then heating the first container to 550 °C.

[0042] In some embodiments, in step S3, the coating agent for carbon coating includes acetylene.

[0043] In some embodiments, in step S3, the time for carbon coating is 2 - 6 h, for example, 4 h.

[0044] In some embodiments, in step S3, the feeding rate for carbon coating is 0.5 - 3 L / min, for example, 1 L / min.

[0045] In some embodiments, in step S3, the carbon coating is carried out under isothermal conditions.

[0046] In some embodiments, in step S3, the temperature of the carbon coating is 500 - 600 °C, such as 550 °C.

[0047] In a certain embodiment of the present invention, the method for preparing the silicon-carbon composite material comprises the following steps:

[0048] Step 1: Weigh 1 kg of porous carbon and place it in a rotary furnace. Weigh 1.1 kg of cyclopentasilane and place it in the first preheating chamber. Among them, the first preheating chamber, the second preheating chamber, the mixed heating chamber, and the rotary furnace are all independently heated;

[0049] After evacuating the first preheating chamber and the second preheating chamber, heat them up to 150 °C at a heating rate of 10 °C / min, and heat the mixed heating chamber up to 180 °C at a heating rate of 10 °C / min;

[0050] Step 2: First, introduce nitrogen at a rate of 500 mL / min into the second preheating chamber. This nitrogen gas sequentially enters the mixed heating chamber and the rotary furnace from the second preheating chamber; after continuously introducing it for 60 min, then introduce nitrogen at a rate of 500 mL / min into the first preheating chamber to carry the cyclopentasilane into the rotary furnace, and continuously introduce it for 90 min;

[0051] Then, cool the rotary furnace in a water bath to 50 °C and keep it for 15 min; then use a vacuum pump to evacuate the system to vacuum; repeat this step 3 times;

[0052] Step 3: Heat the rotary furnace to 250 °C for the first heat preservation, and the time for the first heat preservation is 4 h; then heat the rotary furnace to 500 °C for the second heat preservation, and the time for the second heat preservation is 6 h;

[0053] Step 4: Heat the rotary furnace to 550 °C again, and introduce acetylene into the rotary furnace through the second preheating chamber. The flow rate of acetylene is 1 L / min, and the feeding time is 4 h.

[0054] In a certain embodiment of the present invention, the first preheating chamber, the second preheating chamber, the mixed heating chamber, and the rotary furnace are all set above 100 °C, which can prevent the liquefaction of the preheated gaseous silicon source material.

[0055] The present invention also provides a silicon-carbon composite material, which is prepared by the method for preparing the silicon-carbon composite material as described above.

[0056] The present invention also provides a negative electrode sheet, which comprises the silicon-carbon composite material as described above.

[0057] In the present invention, the negative electrode sheet can be prepared by conventional methods in the art; the preparation method of the negative electrode sheet includes the following steps: coating the mixed slurry of the silicon-carbon composite material, binder and conductive agent on a copper foil after homogenization, followed by vacuum drying, rolling and slitting to obtain the negative electrode sheet. Among them, the formulation of the mixed slurry is as follows: the mass ratio of the silicon-carbon composite material, SP (sulfur / polyacrylonitrile copolymer), SW (sodium silicate), CNT (carbon nanotube), CMC (sodium carboxymethyl cellulose), and SBR (styrene-butadiene rubber) is 90:4.5:0.5:2.5:2.5.

[0058] The present invention also provides a lithium-ion battery, which includes the silicon-carbon composite material or the negative electrode sheet as described above.

[0059] In the present invention, the lithium-ion battery can be prepared by conventional methods in the art, which includes the following steps:

[0060] The preparation method of the electrolyte is as follows: 1M LiPF 6 in EC / DEC (vol% 1:1); 10 vol% of FEC (fluoroethylene carbonate); 1 vol% of VC (vinylene carbonate). Among them, 1M LiPF 6 in EC / DEC (vol% 1:1) means that LiPF 6 is dissolved in a mixture of EC (ethylene carbonate) and DEC (diethyl carbonate) with a volume ratio of 1:1, and its concentration is 1 mol / L;

[0061] Using a polypropylene microporous membrane as the separator and a lithium metal sheet as the counter electrode, the above negative electrode sheet is assembled into a button cell in an inert gas glove box system filled with argon.

[0062] In the present invention, the test method for the electrical properties of the lithium ions is as follows: at 25 °C, use a Blue Power test instrument to perform charge-discharge cycle tests on the assembled lithium-ion battery to obtain data on its capacity, initial Coulomb efficiency, and cycle stability; among them, the program for the charge-discharge cycle test is 0.1C discharge to 5 mV, 0.05C discharge to 5 mV, 0.1C charge to 2V cycle regime: 0.5C discharge to 5 mV, 0.05C discharge to 5 mV, 0.5C charge to 1V.

[0063] On the basis of conforming to common knowledge in the art, the above preferred conditions can be combined arbitrarily to obtain various preferred examples of the present invention.

[0064] The reagents and raw materials used in the present invention are all commercially available.

[0065] The positive and progressive effects of the present invention are as follows:

[0066] 1. The silicon source with a cyclic structure in the present invention is vaporized, and the "capillary condensation" phenomenon occurs during deposition in the micropores of the porous carbon, which can effectively promote the uniformity and depth of deposition. High uniformity can well release stress and improve the long-cycle performance of the material, and good deposition depth can maximize the use of the "inner core" of the material for secondary stress release, further improving the electrical properties of the material, including having long-cycle performance.

[0067] 2. The preparation method of the present invention adopts the process route of vaporization - adsorption - capillary condensation - deposition, disassembling the deposition process of the silicon source material, which is beneficial to controlling its deposition rate and effectively improving the utilization rate of the silicon source material.

[0068] 3. The lithium-ion battery containing the silicon-carbon composite material of the present invention preferably has the following electrical properties: the capacity at 2V is above 1000 mAh / g, the first efficiency at 2V is above 75%, and the capacity retention rate after 500 cycles is above 74%. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 It is a schematic structural diagram of the preparation device of the negative electrode material in the preparation method of Example 1;

[0070] Description of the reference numerals:

[0071] The first preheating chamber 1

[0072] The second preheating chamber 2

[0073] The mixing and heating chamber 3

[0074] The rotary furnace 4

[0075] The vacuum assembly 5

[0076] The first valve 6

[0077] The first pressure detection element 7

[0078] The second valve 8

[0079] The second pressure detection element 9

[0080] The third valve 10

[0081] The third pressure detection element 11

[0082] The fourth valve 12

[0083] The fourth pressure detection element 13

[0084] The fifth valve 14

[0085] The sixth valve 15. DETAILED DESCRIPTION OF THE INVENTION

[0086] The present invention will be further described below by way of examples, but the present invention is not limited to the scope of the described examples. For the experimental methods without specific conditions noted in the following examples, they are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0087] Example 1

[0088] This example provides a preparation device for a negative electrode material, a silicon-carbon composite material and its preparation method, a negative electrode sheet and a lithium-ion battery.

[0089] The preparation device for the negative electrode material includes a raw material pretreatment unit, a deposition coating unit, a vacuum unit, a control unit and an exhaust gas emission unit; the raw material pretreatment unit includes a first preheating chamber 1, a second preheating chamber 2 and a mixed heating chamber 3; the outlet of the first preheating chamber 1 and the outlet of the second preheating chamber 2 are respectively connected to the inlet of the mixed heating chamber 3; the first preheating chamber 1 is used for preheating the first carrier gas or the silicon source material, and the second preheating chamber 2 is used for preheating the carbon source material or the second carrier gas; the deposition coating unit includes a rotary furnace 4; the inlet of the rotary furnace 4 is connected to the outlet of the mixed heating chamber 3; the vacuum unit includes a vacuum assembly 5, and the inlet of the vacuum assembly 5 is connected to the outlet of the rotary furnace 4; the vacuum assembly 5 includes a vacuum pump, a dust collector and a filtering element. The exhaust gas emission unit is connected to the outlet of the vacuum assembly 5; the exhaust gas emission unit includes an alkali liquid tank, a buffer tank, a liquid seal tank and a flame arrester.

[0090] The control unit includes a control center, and a first valve 6, a second valve 8, a third valve 10, a first pressure detection element 7, a second pressure detection element 9, a third pressure detection element 11, a fourth valve 12 and a fourth pressure detection element 13 which are respectively electrically connected to the control center; the first pressure detection element 7 and the first valve 6 are both arranged on the connecting pipeline between the first preheating chamber 1 and the mixed heating chamber 3; the second pressure detection element 9 and the second valve 8 are arranged on the connecting pipeline between the second preheating chamber 2 and the mixed heating chamber 3; the third pressure detection element 11 and the third valve 10 are both arranged on the connecting pipeline between the vacuum assembly 5 and the rotary furnace 4; the fourth valve 12 and the fourth pressure detection element 13 are both arranged on the connecting pipeline between the mixed heating chamber 3 and the rotary furnace 4; the first valve 6, the second valve 8, the third valve 10 and the fourth valve 12 are all solenoid valves.

[0091] Among them, the rotary furnace 4 includes a furnace tube and a driving mechanism for driving the furnace tube to rotate. Inside the furnace tube, there are several material lifting plates and a material conveying device. The material lifting plates are spirally distributed along the furnace tube and are arranged at the inlet end of the furnace tube. The material conveying device is arranged at the outlet end of the furnace tube. Rotating joints are provided at both ends of the furnace tube, and each rotating joint is respectively connected to the connecting pipelines between the mixing and heating chamber 3 and the rotary furnace 4, and the connecting pipelines between the rotary furnace 4 and the vacuum assembly 5. Filters are provided at the ends of each rotating joint to allow gas to pass through and intercept solid materials. Cooling and temperature control devices are independently provided inside the rotary furnace 4, the first preheating chamber 1, the second preheating chamber 2, and the mixing and heating chamber 3;

[0092] A fifth valve 14 is provided at the inlet of the first preheating chamber 1 for regulating the material entering the first preheating chamber 1 electrically or manually by controlling the fifth valve 14 when ventilation is required.

[0093] A sixth valve 15 is provided at the inlet of the second preheating chamber 2 for regulating the material entering the second preheating chamber 2 electrically or manually by controlling the sixth valve 15 when ventilation is required.

[0094] The preparation method of the silicon carbide composite material comprises the following steps:

[0095] Step 1: Weigh 1 kg of porous carbon and place it in the rotary furnace, and weigh 1.1 kg of cyclopentasilane and place it in the first preheating chamber. Among them, the first preheating chamber, the second preheating chamber, the mixing and heating chamber, and the rotary furnace are heated independently;

[0096] After evacuating the first preheating chamber and the second preheating chamber, heat them up to 150 °C at a heating rate of 10 °C / min, and heat the mixing and heating chamber up to 180 °C at a heating rate of 10 °C / min;

[0097] Step 2: First, introduce nitrogen into the second preheating chamber at a rate of 500 mL / min. This nitrogen gas passes through the mixing and heating chamber and the rotary furnace in sequence from the second preheating chamber. After continuously introducing it for 60 min, then introduce nitrogen into the first preheating chamber at a rate of 500 mL / min to carry the cyclopentasilane into the rotary furnace, and continuously introduce it for 90 min;

[0098] Then, cool the rotary furnace in a water bath to 50 °C and keep it for 15 min. After that, use a vacuum pump to evacuate the system to vacuum, and repeat this step 3 times;

[0099] Step 3: Heat the rotary furnace to 250 °C for the first heat preservation, and the time for the first heat preservation is 4 h. Then heat the rotary furnace to 500 °C for the second heat preservation, and the time for the second heat preservation is 6 h;

[0100] Step 4: Heat the rotary kiln to 550 °C again, and introduce acetylene into the rotary kiln through the second preheating chamber. The flow rate of acetylene is 1 L / min, and the feeding time is 4 h to obtain the silicon-carbon composite material.

[0101] The negative electrode sheet of this example is prepared by the following method: The mixed slurry of the above silicon-carbon composite material, binder and conductive agent is homogenized and then coated on the copper foil, and then vacuum dried, rolled and slit to obtain the negative electrode sheet. Among them, the formula of the mixed slurry is: the mass ratio of the silicon-carbon composite material, SP (sulfur / polyacrylonitrile copolymer), SWCNT (single-walled carbon nanotube), CMC (sodium carboxymethyl cellulose), and SBR (styrene-butadiene rubber) is 90:4.5:0.5:2.5:2.5.

[0102] The lithium-ion battery of this example is prepared by the following method:

[0103] The electrolyte ratio is: 1M LiPF 6 in EC / DEC (vol% 1:1) means that LiPF 6 is dissolved in a mixture of EC (ethylene carbonate) and DEC (diethyl phthalate) with a volume ratio of 1:1, and its concentration is 1 mol / L; FEC with a volume percentage of 10%; VC with a volume percentage of 1%;

[0104] Using a polypropylene microporous membrane as the separator and a lithium metal sheet as the counter electrode, the above negative electrode sheet is assembled into a button cell in an inert gas glove box system filled with argon.

[0105] Example 2

[0106] This example provides a preparation device for a negative electrode material, a silicon-carbon composite material and its preparation method, a negative electrode sheet and a lithium-ion battery.

[0107] The preparation method of the silicon-carbon composite material includes the following steps:

[0108] Step 1: Weigh 1.65 kg of cyclopentasilane and place it in the first preheating chamber;

[0109] All other conditions are the same as those in Example 1.

[0110] Example 3

[0111] This example provides a preparation device for a negative electrode material, a silicon-carbon composite material and its preparation method, a negative electrode sheet and a lithium-ion battery.

[0112] The preparation method of the silicon-carbon composite material includes the following steps:

[0113] Step 1: After evacuating the first preheating chamber, heat it to 250 °C at a heating rate of 10 °C / min;

[0114] All other conditions are the same as those in Example 1.

[0115] Example 4

[0116] This example provides a preparation device for a negative electrode material, a silicon-carbon composite material, a preparation method thereof, a negative electrode sheet, and a lithium-ion battery.

[0117] The preparation method of the silicon-carbon composite material includes the following steps:

[0118] Step 1: After evacuating the second preheating chamber, heat it up to 100 °C at a heating rate of 10 °C / min.

[0119] All other conditions are the same as those in Example 1.

[0120] Example 5

[0121] This example provides a preparation device for a negative electrode material, a silicon-carbon composite material, a preparation method thereof, a negative electrode sheet, and a lithium-ion battery.

[0122] The preparation method of the silicon-carbon composite material includes the following steps:

[0123] Step 1: After evacuating the second preheating chamber, heat it up to 250 °C at a heating rate of 10 °C / min.

[0124] All other conditions are the same as those in Example 1.

[0125] Example 6

[0126] This example provides a preparation device for a negative electrode material, a silicon-carbon composite material, a preparation method thereof, a negative electrode sheet, and a lithium-ion battery.

[0127] The preparation method of the silicon-carbon composite material includes the following steps:

[0128] Step 3: Heat the rotary furnace to 150 °C, hold for 4 h, then heat it up to 500 °C and hold for 6 h.

[0129] All other conditions are the same as those in Example 1.

[0130] Example 7

[0131] This example provides a preparation device for a negative electrode material, a silicon-carbon composite material, a preparation method thereof, a negative electrode sheet, and a lithium-ion battery.

[0132] The preparation method of the silicon-carbon composite material includes the following steps:

[0133] Step 3: Heat the rotary furnace to 350 °C, hold for 4 h, then heat it up to 500 °C and hold for 6 h.

[0134] Other conditions are the same as those in Example 1.

[0135] Example 8

[0136] This example provides a preparation device for a negative electrode material, a silicon-carbon composite material, a preparation method thereof, a negative electrode sheet and a lithium-ion battery.

[0137] The preparation method of the silicon-carbon composite material includes the following steps:

[0138] Step 3: Heat the rotary furnace to 350 °C, hold for 2 h, then heat to 500 °C and hold for 6 h;

[0139] Other conditions are the same as those in Example 1.

[0140] Example 9

[0141] This example provides a preparation device for a negative electrode material, a silicon-carbon composite material, a preparation method thereof, a negative electrode sheet and a lithium-ion battery.

[0142] The preparation method of the silicon-carbon composite material includes the following steps:

[0143] Step 3: Heat the rotary furnace to 350 °C, hold for 6 h, then heat to 500 °C and hold for 6 h;

[0144] Other conditions are the same as those in Example 1.

[0145] Example 10

[0146] This example provides a preparation device for a negative electrode material, a silicon-carbon composite material, a preparation method thereof, a negative electrode sheet and a lithium-ion battery.

[0147] The preparation method of the silicon-carbon composite material includes the following steps:

[0148] Step 1: Weigh 1.1 kg of cyclohexylsilane and place it in the first preheating chamber;

[0149] Other conditions are the same as those in Example 1.

[0150] Example 11

[0151] This example provides a preparation device for a negative electrode material, a silicon-carbon composite material, a preparation method thereof, a negative electrode sheet and a lithium-ion battery.

[0152] The preparation method of the silicon-carbon composite material includes the following steps:

[0153] Step 1: Weigh 1.1 kg of decamethylcyclopentasilane and place it in the first preheating chamber;

[0154] Other conditions are the same as those in Example 1.

[0155] Example 12

[0156] The present embodiment provides a device for preparing a negative electrode material, a silicon-carbon composite material and a preparation method thereof, a negative electrode sheet and a lithium-ion battery.

[0157] The preparation method of the silicon-carbon composite material comprises the following steps:

[0158] Step 2: First, introduce 500 mL / min of nitrogen into the second preheating chamber for 60 minutes, and then introduce 500 mL / min of nitrogen into the first preheating chamber for 90 minutes; cool the rotary kiln in a water bath and maintain it at 50°C for 15 minutes; according to the above process, introduce the above materials at one time without recycling;

[0159] Other conditions are the same as in Example 1.

[0160] Comparative Example 1

[0161] This comparative example provides a negative electrode material preparation device, a silicon-carbon composite material and a preparation method thereof, a negative electrode sheet and a lithium-ion battery.

[0162] The preparation method of the silicon-carbon composite material does not include the step of silicon deposition, but only contains the step of carbon coating, which includes the following steps:

[0163] Step 1, weigh 1 kg of porous carbon and place it in a rotary kiln;

[0164] Step 2: Heat the rotary kiln to 550° C. and introduce acetylene into the rotary kiln at a flow rate of 1 L / min for 4 h.

[0165] Comparative Example 2

[0166] This comparative example provides a negative electrode material preparation device, a silicon-carbon composite material and a preparation method thereof, a negative electrode sheet and a lithium-ion battery.

[0167] The preparation method of the silicon-carbon composite material comprises the following steps:

[0168] Step 2, heating the rotary kiln to 250° C. without heat preservation treatment to obtain a carbon material;

[0169] Other conditions are the same as in Example 1.

[0170] Comparative Example 3

[0171] This comparative example provides a negative electrode material preparation device, a silicon-carbon composite material and a preparation method thereof, a negative electrode sheet and a lithium-ion battery.

[0172] The preparation method of the silicon-carbon composite material comprises the following steps:

[0173] Step 1: Weigh 0.55 kg of cyclopentasilane and place it in the first preheating chamber;

[0174] All other conditions are the same as those in Example 1.

[0175] Comparative Example 4

[0176] This comparative example provides a preparation device for a negative electrode material, a silicon-carbon composite material and its preparation method, a negative electrode sheet, and a lithium-ion battery.

[0177] The preparation method of the silicon-carbon composite material includes the following steps:

[0178] Step 1: After evacuating the first preheating chamber, heat it up to 50 °C at a heating rate of 10 °C / min;

[0179] All other conditions are the same as those in Example 1.

[0180] Effect Example 1

[0181] This effect example tested the capacity, first Coulomb efficiency, and cycle stability of the lithium-ion batteries in Examples 1-12 and Comparative Examples 1-4.

[0182] The silicon content of the silicon-carbon composite material was determined by a conventional method in the art: by calculating after calcination in a muffle furnace under air conditions.

[0183] The test method for the above lithium-ion electrical properties is as follows: At 25 °C, use a Blue Power test instrument to perform charge and discharge cycle tests on the assembled lithium-ion battery to obtain data on its capacity, first Coulomb efficiency, and cycle stability; among them, the program for the charge and discharge cycle test is 0.1C discharge to 5 mV, 0.05C discharge to 5 mV, 0.1C charge to 2V cycle mode: 0.5C discharge to 5 mV, 0.05C discharge to 5 mV, 0.5C charge to 1V, and the results of the 2V capacity and 2V first efficiency are obtained, as shown in Table 1; Table 1 shows the electrical properties of the lithium-ion batteries in each example and comparative example.

[0184] Table 1

[0185]

[0186] As can be seen from the above table, the 2V capacity of the lithium-ion batteries prepared from the silicon-carbon composite materials in Examples 1-12 is above 1000 mAh / g, the 2V first efficiency is above 75%, and the capacity retention rate after 500 cycles is above 74%.

[0187] For Comparative Example 1, since there is no gas deposition step containing a silicon source material, when the prepared silicon-carbon composite material is further used to prepare a lithium-ion battery, its 2V capacity, 2V first efficiency, and capacity retention rate after 2500 cycles are all low.

[0188] For Comparative Example 2, since no heat preservation treatment was carried out and the chemical vapor deposition temperature of the present application was not reached, the 2V capacity, the first efficiency at 2V, and the capacity retention rate after 2500 cycles of the lithium-ion battery containing this silicon-carbon composite material were all low.

[0189] For Comparative Example 3, the amount of the silicon source material was small, resulting in poor electrical properties of the lithium-ion battery containing this silicon-carbon composite material.

[0190] For Comparative Example 4, since the temperature of the first preheating chamber did not reach the vaporization temperature of cyclopentasilane; cyclopentasilane was not carried into the rotary furnace by nitrogen, resulting in only a small amount of silicon being deposited on the porous carbon, reducing its electrical properties.

Claims

1. A method for preparing a silicon-carbon composite material, characterized in that: It includes the following steps: S1, transporting the preheated and vaporized silicon source material to a first container containing porous carbon through a first carrier gas; the silicon source material has a ring structure; the mass ratio of the silicon source material to the porous carbon is (0.6-1.65):1; the preheating temperature of the silicon source material is 100-250°C; S2, subjecting the first container to a heat preservation treatment to obtain a carbon material; the temperature of the heat preservation treatment is 450° C. or above; and the time of the heat preservation treatment is 4-10 hours; S3. Carbon coating the carbon material to obtain a silicon-carbon composite material.

2. The method for preparing the silicon-carbon composite material according to claim 1, characterized in that: The method for preparing the silicon-carbon composite material is carried out in a negative electrode material preparation device, which comprises a first preheating chamber, a mixing heating chamber, a first container and a vacuum assembly; the outlet of the first preheating chamber is connected to the inlet of the mixing heating chamber; the first preheating chamber is used to preheat a first carrier gas and a silicon source material; the first container comprises a rotary kiln; the inlet of the rotary kiln is connected to the outlet of the mixing heating chamber; the inlet of the vacuum assembly is connected to the outlet of the rotary kiln; Preferably, the negative electrode material preparation device further comprises a second preheating chamber, the outlet of the second preheating chamber is connected to the inlet of the mixing heating chamber; the second preheating chamber is used to preheat the second carrier gas; More preferably, the negative electrode material preparation device further comprises a control unit; the control unit comprises a control center, and a first valve, a second valve, a third valve, a first pressure detection element, a second pressure detection element and a third pressure detection element electrically connected to the control center respectively; the first pressure detection element and the first valve are both arranged in the connecting pipeline between the first preheating chamber and the mixing heating chamber; the second pressure detection element and the second valve are arranged in the connecting pipeline between the second preheating chamber and the mixing heating chamber; the third pressure detection element and the third valve are both arranged in the connecting pipeline between the vacuum component and the rotary kiln; Preferably, the rotary kiln comprises a furnace tube and a driving mechanism, and the driving mechanism is used to drive the furnace tube to rotate; More preferably, a plurality of material lifting plates and material conveying devices are provided inside the furnace tube; the material lifting plates are distributed in a spiral shape along the furnace tube and are provided at the inlet end of the furnace tube; the material conveying device is provided at the outlet end of the furnace tube; More preferably, both ends of the furnace tube are provided with rotary joints, and each rotary joint is respectively connected to the connecting pipe between the mixing heating chamber and the rotary kiln, and the connecting pipe between the rotary kiln and the vacuum component; further preferably, a filter element is provided at the end of each rotary joint to allow gas to pass through and intercept solid materials; Preferably, the vacuum assembly comprises a vacuum pump, a dust collector and a filter element connected in sequence; Preferably, the negative electrode material preparation device further comprises a tail gas emission unit; the tail gas emission unit is connected to the outlet of the vacuum component; more preferably, the tail gas emission unit comprises an alkali liquid tank, a buffer tank, a liquid sealing tank and a flame arrester; More preferably, the rotary kiln, the first preheating chamber, the second preheating chamber, and the mixing heating chamber are each independently provided with a cooling temperature control device; Preferably, the control unit also includes a fourth valve and a fourth pressure detection element electrically connected to the control center respectively, and the fourth valve and the fourth pressure detection element are both arranged in the connecting pipeline between the mixing heating chamber and the rotary kiln; the first valve, the second valve, the third valve and the fourth valve are all solenoid valves.

3. The method for preparing the silicon-carbon composite material according to claim 1, characterized in that: Step S1 satisfies one or more of the following conditions: ① The mass ratio of the silicon source material to the porous carbon is (0.6-1.4):1, preferably (0.8-1.1):1, for example 1.1:1; ② The silicon source material includes cyclic liquid silane; preferably, the silicon source material is one or more of cyclopentasilane, cyclotetrasilane, cyclohexasilane and decamethylcyclopentasilane, more preferably cyclopentasilane; ③The first carrier gas includes nitrogen; ④ The delivery rate of the first carrier gas is 500-1000mL / min; ⑤ The delivery duration of the first carrier gas is 60-120 minutes, preferably 90-120 minutes; ⑥ After the silicon source material is introduced into the first container, the first container is cooled; preferably, the cooling temperature is 50-150°C, for example, 50°C; preferably, the cooling time is 10-30 minutes, for example, 15 minutes.

4. The method for preparing the silicon-carbon composite material according to claim 1, characterized in that: In step S1, the conveying process of the silicon source material further comprises the following cyclic steps: introducing a second carrier gas into the first container containing porous carbon; conveying the preheated and vaporized silicon source material to the first container containing porous carbon through the first carrier gas, and cooling the first container; and then evacuating the first container to a vacuum; Preferably, the second carrier gas comprises nitrogen; Preferably, the gas velocity of the second carrier gas is 500-1000 mL / min; Preferably, the second carrier gas is introduced for 30-120 minutes.

5. The method for preparing the silicon-carbon composite material according to claim 4, characterized in that: The cycle was repeated 3 times.

6. The method for preparing the silicon-carbon composite material according to claim 1, characterized in that: In step S2, before the first container is subjected to the heat preservation treatment, the first container is subjected to the heat raising treatment, and the temperature of the heat raising treatment is 150-600° C.; Preferably, the temperature control program of the first container comprises the following steps: firstly, heating the first container to 150-350°C for a first heat preservation, wherein the first heat preservation time is 2-4 hours; then heating the first container to 450-600°C for a second heat preservation, wherein the second heat preservation time is 4-8 hours; More preferably, the temperature control program of the first container includes the following steps: firstly, the temperature of the first container is increased to 250°C for the first insulation, and the first insulation time is 4 hours; then, the temperature of the first container is increased to 500°C for the second insulation, and the second insulation time is 6 hours; then, the temperature of the first container is increased to 550°C again.

7. The method for preparing the silicon-carbon composite material according to claim 1, characterized in that: Step S3 satisfies one or more of the following conditions: ① The carbon-coated coating agent includes acetylene; ② The carbon coating time is 2-6h; ③ The feeding rate of the carbon coating is 0.5-3L / min; ④ The carbon coating is carried out under constant temperature conditions; ⑤The temperature of the carbon coating is 500-600°C.

8. A silicon-carbon composite material, characterized in that: The silicon-carbon composite material is prepared by the preparation method of the silicon-carbon composite material according to any one of claims 1 to 7.

9. A negative electrode sheet, characterized in that: It comprises the silicon-carbon composite material as claimed in claim 8.

10. A lithium ion battery, characterized in that: It includes the silicon-carbon composite material as claimed in claim 8 or the negative electrode sheet as claimed in claim 9.

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