Silicon-carbon negative electrode material and preparation method thereof, negative electrode plate and battery

Abstract

The embodiment of the invention provides a silicon-carbon negative electrode material and a preparation method thereof, a negative electrode plate and a battery, the silicon-carbon negative electrode material comprises a silicon-carbon inner core and a coating layer coating the silicon-carbon inner core, and the silicon-carbon inner core comprises a porous carbon substrate and nanometer silicon arranged on the porous carbon substrate. The test result of the first cyclic volt-ampere test of the silicon carbon negative electrode material meets at least one of the following conditions: (a) the value of dQ / (dV * C) of a discharge differential capacity curve in a voltage interval of 0.45 V + / -0.05 V is less than or equal to 1.7, dQ / dV represents differential capacity, the unit is mAh / V, C represents charge capacity, and the unit is mAh; (b) no sharp peak exists in a discharge differential capacity curve in a voltage interval of 0.45 V + / -0.05 V, the battery can present a smooth and stable discharge process, the capacity retention ratio and the stability of the battery after circulation are improved, and the preparation method is simple, convenient and feasible, and is suitable for industrial production.

Description

Technical Field

[0001] The present application belongs to the field of battery material technology, and in particular relates to a silicon-carbon negative electrode material and a preparation method thereof, a negative electrode sheet and a battery. Background Art

[0002] At present, the industry often uses chemical vapor deposition to deposit silicon and coated carbon materials on the surface of porous carbon in sequence to prepare silicon-carbon negative electrode materials to limit the volume expansion of silicon. Among them, the degree of accommodation of nano-silicon by the porous carbon substrate and the carbon coating layer is an important indicator for inhibiting the volume expansion of silicon. Only by depositing silicon and carbon coating layers on the surface of the porous carbon substrate by chemical vapor deposition, the silicon in the pores of the porous carbon substrate can be constrained at most, and the bonding strength between the porous carbon substrate and the carbon coating layer is often insufficient to fully inhibit the volume expansion of silicon between the surface of the porous carbon substrate and the carbon coating layer. Therefore, it is still difficult to avoid the violent silicon-lithium alloy reaction caused by silicon expansion during battery cycling, and the deposited carbon coating layer is prone to problems such as excessive pores or uneven thickness, which makes the silicon at the pore mouth or outer surface of the porous carbon exposed to the air and generates inactive silicon oxide. The volume expansion of silicon and the irreversible reduction reaction of silicon oxide are not conducive to building a long-term stable and uniform charge and discharge process, which leads to significant attenuation of battery capacity after multiple cycles. Summary of the Invention

[0003] In view of this, the present invention provides a silicon-carbon anode material and its preparation method, a negative electrode plate, and a battery. This silicon-carbon anode material effectively avoids capacity decay caused by silicon expansion or silicon oxide side reactions during battery cycling. Its discharge differential capacity curve in the first cyclic voltammetry test exhibits a uniform and smooth platform in the voltage range of 0.45V±0.05V, which helps promote a smooth discharge process for the battery and improves capacity retention and stability after multiple cycles.

[0004] In a first aspect, an embodiment of the present application provides a silicon-carbon negative electrode material, comprising a silicon-carbon core and a coating layer coating the silicon-carbon core, wherein the silicon-carbon core comprises a porous carbon substrate and nano-silicon disposed on the porous carbon substrate; The test results of the first cyclic voltammetry test of the silicon-carbon negative electrode material meet at least one of the following conditions: (a) The discharge differential capacity curve has a value of dQ / (dV×C) less than or equal to 1.7 in the voltage range of 0.45V±0.05V. dQ / dV represents the differential capacity in mAh / V, and C represents the charge capacity in mAh. (b) The discharge differential capacity curve has no sharp peak in the voltage range of 0.45V±0.05V.

[0005] In the embodiment of the present application, in the first cyclic voltammetry test of the silicon-carbon negative electrode material, the discharge capacity in the voltage range of 0.45V±0.05V accounts for less than or equal to 4% of the total discharge capacity.

[0006] In the embodiment of the present application, the silicon-carbon negative electrode material satisfies at least one of the following conditions: (a) the particle size D of the silicon-carbon negative electrode material V 50 is 5μm~10μm; (b) the mass percentage of silicon element in the silicon-carbon negative electrode material is 40%~75%; (c) the powder resistivity of the silicon-carbon negative electrode material under a test pressure of 30MPa is less than or equal to 10Ω·cm; (d) in the silicon-carbon negative electrode material, the thickness of the coating layer is 1nm~100nm. In a second aspect, an embodiment of the present application provides a method for preparing the silicon-carbon negative electrode material provided in the first aspect of the present application, comprising: placing a silicon-carbon core in an atmosphere containing a carbon source gas for deposition to obtain a silicon-carbon negative electrode material intermediate; The silicon-carbon negative electrode material intermediate is heat-treated to obtain a silicon-carbon negative electrode material. The heat treatment temperature is 400° C. to 750° C., and the heat treatment time is 1 hour to 6 hours.

[0007] In the embodiment of the present application, the deposition temperature is 450° C. to 650° C., and the deposition time is 0.5 h to 16 h.

[0008] In an embodiment of the present application, the atmosphere containing the carbon source gas also includes a carrier gas. During deposition, the flow rate of the carbon source gas is 1 L / min to 10 L / min, and the flow rate of the carrier gas is 1 L / min to 60 L / min; the carbon source gas includes one or more of alkanes, alkenes, alkynes, alcohols and carbonates.

[0009] In an embodiment of the present application, the preparation of the silicon-carbon core includes: placing a porous carbon substrate in an atmosphere containing a silicon source gas to perform silicon deposition to obtain a silicon-carbon core; the atmosphere containing the silicon source gas also includes an initial carrier gas, and during the silicon deposition, the flow rate of the silicon source gas is 5L / min~10L / min, and the flow rate of the initial carrier gas is 40L / min~60L / min; the silicon source gas includes one or more of monosilane, disilane and chlorosilane.

[0010] In the embodiment of the present application, the temperature of silicon deposition is 500° C. to 600° C., the pressure is 2 KPa to 10 KPa, and the time is 8 h to 30 h.

[0011] In a third aspect, an embodiment of the present application provides a negative electrode plate, comprising a negative electrode current collector and a negative electrode active material layer arranged on at least one side surface of the negative electrode current collector, the negative electrode active material layer comprising the silicon-carbon negative electrode material provided in the first aspect or the silicon-carbon negative electrode material prepared by the preparation method provided in the second aspect.

[0012] In a fourth aspect, an embodiment of the present application further provides a battery, comprising a positive electrode plate and the negative electrode plate provided in the third aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. The specific embodiments described here are only used to explain the present application and are not used to limit the present application.

[0014] Figure 1 A flow chart for preparing a silicon-carbon negative electrode material according to an embodiment of the present application; Figure 2 A flow chart for preparing a silicon-carbon negative electrode material according to another embodiment of the present application; Figure 3 This is a differential capacity curve of the first cyclic voltammetry test of the silicon-carbon negative electrode material prepared in Example 2 of the present application; Figure 4 This is a differential capacity curve diagram of the first cyclic voltammetry test of the silicon-carbon negative electrode material prepared in Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0015] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0016] The theoretical specific capacity of silicon is as high as 4200mAh / g, which is much higher than that of graphite negative electrode. Therefore, it has attracted extensive attention in the field of battery materials due to its high energy density and low lithium insertion potential. The silicon-lithium alloying reaction that occurs when silicon-based materials are used as negative electrodes is a first-order phase transition reaction, which directly transforms from pure silicon (Si) to a high lithium content alloy (such as Li 15 Si4 or Li 22Si5) is accompanied by a volume expansion of approximately 300%. To address the volume expansion problem of silicon materials, existing technologies often use porous carbon substrates to accommodate silicon and coat it with a carbon layer to spatially confine the silicon material. However, in related processes, only chemical vapor deposition is used to sequentially deposit nanosilicon and a carbon coating layer on a porous carbon substrate. This inevitably results in gaps due to insufficient bonding between the carbon coating layer and the porous carbon. This, at best, can ensure that the nanosilicon in the pores of the porous carbon substrate is confined. However, for the nanosilicon deposited at the pore openings and outer surface of the porous carbon substrate, there is still space for it to move freely and expand in volume. These nanosilicon floating on the outer surface of the porous carbon substrate (hereinafter referred to as "floating silicon") expand in volume because they are not sufficiently constrained, which can lead to a violent silicon-lithium alloying reaction during battery cycling. Furthermore, carbon coatings produced by chemical vapor deposition are prone to problems such as excessive pores or uneven thickness, which not only hinders the volume control of silicon but can also cause silicon to oxidize and form silicon oxides. Silicon oxides are susceptible to irreversible reduction reactions with lithium ions during battery cycling, severely consuming the lithium source. Both the aforementioned silicon-lithium alloying reaction and the irreversible reduction reaction of silicon oxides are detrimental to establishing a long-term, stable, and uniform charge-discharge process, resulting in significant battery capacity degradation after multiple cycles.

[0017] The embodiment of the present application provides a silicon-carbon negative electrode material, comprising a silicon-carbon core and a coating layer covering the silicon-carbon core, wherein the silicon-carbon core comprises a porous carbon substrate and nano-silicon disposed on the porous carbon substrate; The results of the first cyclic voltammetry test of the silicon-carbon negative electrode material meet at least one of the following conditions: (a) The discharge differential capacity curve has a value of dQ / (dV×C) less than or equal to 1.7 in the voltage range of 0.45V±0.05V. dQ / dV represents the differential capacity in mAh / V, and C represents the charge capacity in mAh. (b) The discharge differential capacity curve has no sharp peak in the voltage range of 0.45V±0.05V.

[0018] In the silicon-carbon negative electrode material provided in the embodiments of the present application, the silicon-carbon core is tightly combined with the coating layer, firmly fixing the nano-silicon in the pores and / or outer surface of the porous carbon substrate, making it difficult for it to move freely or expand in volume, effectively reducing the violent silicon-lithium alloying reaction caused by floating silicon during the battery cycle.

[0019] In particular, the differential capacity (dQ / dV) analysis of the discharge curve of the silicon-carbon negative electrode material shows that the value of dQ / (dV×C) of the discharge differential capacity curve in the voltage range of 0.45V±0.05V never exceeds 1.7, and / or, the discharge differential capacity curve has no sharp peak in the voltage range of 0.45V±0.05V, which is significantly different from the characteristic peaks that appear in this area of ​​traditional silicon-based materials. Its discharge differential capacity curve presents a uniform and smooth platform in the voltage range of 0.45V±0.05V, indicating that the material has very little or no violent silicon-lithium alloying reaction and irreversible reduction reaction of silicon oxide in this potential window, which means that the volume expansion of nano-silicon in the silicon-carbon negative electrode material is fully suppressed, and the silicon oxide content is relatively low, which can effectively avoid local concentrated discharge and lithium loss during the battery cycle, thereby effectively improving the capacity retention rate and cycle stability of the battery.

[0020] In this embodiment, the first cyclic voltammetry test of the silicon-carbon anode material was conducted using a button-type half-cell. Specifically, the silicon-carbon anode material was fabricated into a negative electrode sheet, and a lithium sheet was used as the counter electrode. This was then assembled into a button-type half-cell with a lithium salt ester electrolyte and a polyethylene (PE) separator. Cyclic voltammetry was performed on the button-type half-cell at 25°C using a Blue Electric electrochemical station. The scan voltage range was set to 0.05V–1.5V, the scan rate was set to 0.1mV / s, the number of scan segments was set to 6, and the sampling interval was set to 0.001V.

[0021] In the embodiment of the present application, in the first cyclic voltammetry test results of the silicon-carbon negative electrode material, the value of dQ / (dV×C) of the discharge differential capacity curve in the voltage range of 0.45V±0.05V is less than or equal to 1.7, and can be, but not limited to, 0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.5, 1.57, 1.6, 1.61, 1.63, 1.64, 1.65, 1.66, 1.68, or 1.7. In the embodiment of the present application, the differential capacity dQ / dV represents the change in charge per unit voltage change, and its unit is mAh / V. C represents the charge capacity, and its unit is mAh. dQ / (dV×C) is a standardized parameter in the cyclic voltammetry method, which is used to eliminate the influence of the charge capacity on the differential capacity signal, and its unit is V -1 .

[0022] During the battery cycle of silicon-based negative electrode materials of lithium-ion batteries, silicon (Si) will react with lithium (Li) to form lithium-silicon alloy (Li x Si), the corresponding reaction is Si+xLi + +xe - →Li xIn the discharge differential capacity curve of Si in the cyclic voltammetry test, the differential capacity value corresponding to the voltage of about 0.45V is positively correlated with the intensity of the lithiation reaction of nano-silicon, that is, the stronger the lithiation reaction, the higher the differential capacity value corresponding to this voltage, and the intensity of the silicon-lithium alloying reaction is positively correlated with the volume expansion of silicon. In addition, if silicon oxide (such as SiO2) exists in the silicon-carbon negative electrode material, it will undergo an irreversible reduction reaction SiO2+4Li that consumes the lithium source during the lithium battery cycle. + +4e - →Si+2Li2O, corresponding to the discharge differential capacity curve of the cyclic voltammetry test, the reduction peak usually also appears in the voltage range of 0.4V~0.6V, and its peak value has a positive correlation with the intensity of the reduction reaction.

[0023] In the embodiment of the present application, the value of dQ / (dV×C) in the voltage range of 0.45V±0.05V reflects the degree of inhibition of the violent reaction of silicon-lithium alloying and the reduction reaction of silicon oxide. The lower the value, the lower the content of silicon oxide in the silicon-carbon negative electrode material, and also the higher the degree of bonding between the active nano-silicon and the porous carbon substrate, which effectively inhibits the volume expansion of the active nano-silicon. The two inhibit or reduce the Li-ion reduction reaction through stress and potential coupling. 15 The formation of Si4 makes the battery present a smooth and uniform discharge process. The discharge differential capacity curve of the silicon-carbon negative electrode material of this application shows that the value of dQ / (dV×C) is always less than or equal to 1.7 in the voltage range of 0.45V±0.05V. This situation proves that the silicon expansion in the silicon-carbon negative electrode material is fully suppressed during the discharge process and no violent silicon-lithium alloying reaction occurs. In addition, the content of silicon oxide in the silicon-carbon negative electrode material is low and no obvious irreversible reduction reaction of silicon oxide occurs. That is, the reaction intensity in the voltage range of 0.45V±0.05V mainly comes from the stable discharge reaction.

[0024] In the embodiment of the present application, in the first cyclic voltammetry test of the silicon-carbon negative electrode material, the discharge differential capacity curve does not have a sharp peak in the voltage range of 0.45V±0.05V. In some embodiments of the present application, the discharge differential capacity curve is smooth without a convex peak in the voltage range of 0.45V±0.05V. In some embodiments of the present application, the discharge differential capacity curve has a gentle convex peak in the voltage range of 0.45V±0.05V, and the gentle convex peak is defined as the absolute value of the curve change rate (|△(dQ / dV) / △V|) of the voltage point corresponding to its peak value and the adjacent 0.01V interval of the voltage point is less than or equal to 40. This means that the discharge differential capacity curve does not show a sudden change in the voltage range of 0.45V±0.05V, that is, the curve always tends to a flat state, which reflects that the silicon in the system has not undergone excessive expansion, and the lithium alloying reaction of the floating silicon is suppressed or kinetically homogenized, so there is no drastic phase change caused by rapid silicon-lithium alloying. This is beneficial to improving the stability and durability of battery cycles.

[0025] In an embodiment of the present application, in the first cyclic voltammetry test of the silicon-carbon negative electrode material, the discharge capacity in the voltage range of 0.45V±0.05V accounts for less than or equal to 4% of the total discharge capacity. The total discharge capacity here refers to the total discharge capacity of the silicon-carbon negative electrode material within the full voltage range (0.05V~1.5V) in the first cyclic voltammetry test. In some embodiments of the present application, the discharge capacity in the voltage range of 0.45V±0.05V accounts for, for example, but not limited to, 0.5%, 1%, 1.5%, 2%, 2.73%, 2.91%, 3%, 3.07%, 3.11%, 3.19%, 3.24%, 3.26%, 3.28%, 3.31%, 3.5%, 3.8%, and 4%. This means that the violent concentrated discharge and lithium loss caused by the violent silicon-lithium alloying reaction and the irreversible reduction reaction of silicon oxide can be basically eliminated. The discharge process always presents a uniform and gentle lithiation reaction, which is conducive to the construction of long-term stable battery cycle.

[0026] In an embodiment of the present application, the silicon-carbon core includes a porous carbon substrate and nano-silicon disposed on the porous carbon substrate. The nano-silicon is a silicon particle with a size between 1 nm and 100 nm in at least one spatial dimension (length, width, height or diameter), which is distributed in the pores and / or outer surface of the porous carbon substrate. In the embodiment of the present application, the microporosity of the porous carbon substrate is 70% to 95%, and the mesoporosity is 5% to 30%. Micropores are pores with a pore diameter less than or equal to 2 nm, and mesopores are pores with a pore diameter between 2 nm and 50 nm. In some embodiments of the present application, the microporosity may be, but is not limited to, 70%, 75%, 80%, 85%, 90%, 93.41%, and 95%, and the mesoporosity may be, but is not limited to, 5%, 6.6%, 10%, 15%, 20%, 25%, and 30%. The pores in the porous carbon substrate are dominated by micropores and supplemented by mesopores, which can make the porous carbon substrate have a higher specific surface area to provide more nano-silicon adsorption sites, and an appropriate amount of mesopores can provide more expansion space for nano-silicon, which helps to improve the gram capacity and anti-expansion properties of the silicon-carbon negative electrode material at the same time. In some specific embodiments of the present application, the microporosity of the porous carbon substrate is 80% to 95%, and the mesoporosity is 5% to 10%.

[0027] In the embodiment of the present application, the specific surface area of ​​the porous carbon substrate is 1800 m 2 / g~2600m 2 / g, for example, but not limited to 1800m 2 / g、1900m 2 / g、2000m 2 / g、2100m 2 / g、2200m 2 / g、2300m 2 / g、2400m 2 / g、2500m 2 / g、2600m 2 The porous carbon substrate has a suitable specific surface area, which can provide sufficient nano-silicon adsorption sites, helping to improve the bonding strength between nano-silicon and the porous carbon substrate and reduce the risk of nano-silicon detachment to a certain extent.

[0028] In embodiments of the present application, the porous carbon substrate has a crushing force of 8 mN to 30 mN, and may include, but is not limited to, 8 mN, 10 mN, 14.97 mN, 15 mN, 20 mN, 25 mN, and 30 mN. The porous carbon substrate has an appropriate crushing force to avoid being too rigid or too soft to accommodate the volume expansion of silicon. In some specific embodiments of the present application, the crushing force of the porous carbon substrate is 9 mN to 16 mN.

[0029] In an embodiment of the present application, the coating layer completely covers the silicon-carbon core. In some embodiments of the present application, the coating layer includes a carbon layer; in other embodiments of the present application, the coating layer includes a passivation layer and a carbon layer. Specifically, the passivation layer completely covers the silicon-carbon core, and the carbon layer completely covers the passivation layer. The material of the passivation layer includes one or more of carbon, oxygen-containing carbon, fluorine-containing carbon and polycarbonate. The thickness of the passivation layer is less than the thickness of the carbon layer, and the density of the passivation layer is greater than the density of the carbon layer, that is, the passivation layer closer to the nano-silicon is denser than the carbon layer, which can reduce the probability of nano-silicon being oxidized to a greater extent, and the thicker carbon layer has more pores than the passivation layer, which can provide a smooth transmission path for lithium ions in the electrolyte to migrate inward and undergo electrochemical reactions with silicon.

[0030] In the embodiment of the present application, the thickness of the coating layer is 1nm~100nm, for example, it can be but not limited to 1nm, 5nm, 10nm, 20nm, 40nm, 60nm, 80nm, 100nm. The coating layer serves as a physical barrier to the silicon-carbon core. When its thickness is within the above range, a shell structure with better strength is formed, which is sufficient to resist and buffer the volume expansion of nano-silicon in the silicon-carbon core, while avoiding the shell being too thick and increasing the difficulty of lithium ion migration inward, which can give the silicon-carbon negative electrode material better anti-expansion and ionic conductivity. In some specific embodiments of the present application, the thickness of the coating layer in the silicon-carbon negative electrode material is 5nm~20nm.

[0031] In the embodiments of the present application, the mass percentage of silicon in the silicon-carbon negative electrode material is 40% to 75%, for example, it can be but not limited to 40%, 45%, 50%, 55%, 58.19%, 58.47%, 58.64%, 59.01%, 60%, 65%, 70%, and 75%. Based on the inherent property of silicon material with high specific capacity, the appropriate silicon content can ensure that the silicon-carbon negative electrode material has a higher gram capacity while avoiding the reduction of the conductivity of the silicon-carbon negative electrode material due to excessive silicon content. In some specific embodiments of the present application, the mass percentage of silicon in the silicon-carbon negative electrode material is 55% to 65%.

[0032] In the embodiment of the present application, the particle size D of the silicon-carbon negative electrode material V 50 is 5μm~10μm, particle size D V 50 refers to the particle size corresponding to the cumulative particle size distribution percentage reaching 50%, also called the median particle size or median particle size. Its physical meaning is that particles with a particle size greater than this value account for 50%, and particles with a particle size less than this value also account for 50%. In some embodiments of the present application, the particle size D of the silicon-carbon negative electrode material VFor example, 50 may be, but is not limited to, 5 μm, 6 μm, 6.833 μm, 7 μm, 7.633 μm, 7.7 μm, 7.759 μm, 7.768 μm, 7.791 μm, 7.798 μm, 7.819 μm, 7.844 μm, 7.872 μm, 7.913 μm, 7.961 μm, 7.993 μm, 8 μm, 8.051 μm, 9 μm, and 10 μm. The silicon-carbon negative electrode material has a suitable particle size D V 50 is conducive to increasing the gap between particles to relieve expansion stress, while avoiding the reduction of electrode compaction density and battery energy density due to too small volume.

[0033] In an embodiment of the present application, the powder resistivity of the silicon-carbon negative electrode material at a test pressure of 30 MPa is less than or equal to 10Ω·cm, for example, but not limited to, 0.5Ω·cm, 0.7Ω·cm, 1Ω·cm, 1.4Ω·cm, 1.43Ω·cm, 1.51Ω·cm, 1.57Ω·cm, 1.59Ω·cm, 1.61Ω·cm, 1.64Ω·cm, 1.66Ω·cm, 1.68Ω·cm, 1.72Ω·cm, 1.73Ω·cm, 1.74Ω·cm, 2Ω·cm, 3Ω·cm, 4Ω·cm, 5Ω·cm, 6Ω·cm, 7Ω·cm, 8Ω·cm, 9Ω·cm, and 10Ω·cm. In some specific embodiments of the present application, the powder resistivity of the silicon-carbon negative electrode material at a test pressure of 30 MPa is 0.7Ω·cm~6Ω·cm.

[0034] In an embodiment of the present application, a silicon-carbon negative electrode material and a lithium sheet are assembled into a CR2016 type button half-cell, and a cycle performance test is performed. The specific cycle steps are: charging to 4.2V at a constant current (CC) of 1C, then switching to constant voltage (CV) charging until the current drops to 0.05C, stopping, and then standing for 10 minutes. After that, discharge to 3.0V at 1C CC, which is one week. The capacity retention rate of the button half-cell after 100 cycles is greater than or equal to 89%, for example, but not limited to, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, and 99%.

[0035] In the embodiment of the present application, the thickness of the coating layer is measured by transmission electron microscopy; the particle size distribution laser diffraction method is used to detect the particle size D of the silicon carbon negative electrode material. V 50; a powder resistivity tester was used to detect the powder resistivity of the silicon-carbon negative electrode material; a thermogravimetric analysis method was used to detect the mass percentage of the silicon element; a nitrogen adsorption specific surface area analysis method combined with the BET (Brunauer Emmett Teller) method was used to detect the specific surface area of ​​the porous carbon substrate; a single particle mechanical property testing system (particle crush tester) was used to detect the crushing force of the porous carbon matrix. In the silicon-carbon negative electrode material provided in the embodiment of the present application, the silicon-carbon core is tightly combined with the coating layer, and there is little space between the two for nano-silicon to move freely or expand, so that the nano-silicon is firmly fixed in the pores of the porous carbon substrate and / or between the surface of the porous carbon substrate and the passivation layer, reducing the violent silicon-lithium alloy reaction caused by the expansion of floating silicon during battery cycling. On this basis, the presence of the passivation layer reduces the degree of silicon oxidation, can reduce the irreversible reduction reaction of silicon oxide, and at the same time avoid the adverse effects of the two adverse reactions on the battery cycle, thereby jointly improving the cycle capacity retention rate of the silicon-carbon negative electrode material. Further designing the physical characteristics of the silicon-carbon negative electrode material, such as particle size and silicon content, can greatly improve the overall electrochemical performance of the silicon-carbon material.

[0036] The present invention provides a method for preparing the aforementioned silicon-carbon negative electrode material, and the preparation process is as follows: Figure 1 As shown, the following steps are included: S101: placing the silicon-carbon core in an atmosphere containing a carbon source gas for deposition to obtain a silicon-carbon negative electrode material intermediate; S102: heat-treating the silicon-carbon negative electrode material intermediate to obtain a silicon-carbon negative electrode material. The heat-treatment temperature is 400° C. to 750° C., and the heat-treatment time is 1 h to 6 h.

[0037] An embodiment of the present application provides a method for preparing a silicon-carbon negative electrode material, which includes coating and heat treating a silicon-carbon core. The heat treatment can effectively compress the interlayer gaps, enhance the wrapping strength of the coating layer on the silicon-carbon core, and optimize the uniformity and density of the coating layer, thereby improving the volume constraint and physical isolation of nano-silicon. The nano-silicon in the prepared silicon-carbon negative electrode material is fully constrained and has a low degree of oxidation. Accordingly, the proportion of active silicon is greater. The silicon-carbon negative electrode material battery exhibits a smooth and stable discharge state during the cycle, giving the battery better cycle stability.

[0038] In another embodiment of the present application, the preparation process of the silicon-carbon negative electrode material is as follows: Figure 2 As shown, the method further includes step S100: placing the porous carbon substrate in an atmosphere containing a silicon source gas to perform silicon deposition, so as to deposit nano-silicon in the pores and / or on the outer surface of the porous carbon substrate to obtain a silicon-carbon core.

[0039] In step S100 , the silicon source gas includes but is not limited to one or more of monosilane, disilane and chlorosilane.

[0040] In the embodiment of the present application, the atmosphere containing the silicon source gas further includes an initial carrier gas, which is an inert gas.

[0041] In some embodiments of the present application, the temperature of silicon deposition is 500°C~600°C, for example, it can be but not limited to 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C, and 600°C; the time of silicon deposition is 8h~30h, for example, it can be but not limited to 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h, 26h, 28h, and 30h; the pressure of silicon deposition is 2KPa~10KPa, for example, it can be but not limited to 2KPa, 3KPa, 4KPa, 5KPa, 6KPa, 7KPa, 8KPa, 9KPa, and 10KPa.

[0042] In the embodiment of the present application, during the silicon deposition process, the flow rate of the silicon source gas is 5L / min~10L / min, for example, it can be but not limited to 5L / min, 6L / min, 7L / min, 8L / min, 9L / min, 10L / min; the flow rate of the initial carrier gas is 40L / min~60L / min, for example, it can be but not limited to 40L / min, 43L / min, 45L / min, 50L / min, 55L / min, 60L / min.

[0043] In step S101, a coating layer is formed by deposition on the surface of the silicon-carbon core to obtain a silicon-carbon negative electrode material intermediate.

[0044] In some embodiments of the present application, the deposition includes carbon deposition, and correspondingly, the initial coating layer formed by carbon deposition is an initial carbon layer.

[0045] In some other embodiments of the present application, deposition includes passivation treatment and carbon deposition. Correspondingly, the passivation treatment forms an initial passivation layer on the surface of the silicon-carbon core, and carbon deposition forms an initial carbon layer on the surface of the passivation layer. That is, the initial coating formed by deposition includes an initial passivation layer and an initial carbon layer. The purpose of passivation treatment of the silicon-carbon core is to directly block the contact of nano-silicon with oxygen or water in the air, minimize the probability of nano-silicon being converted into inactive silicon oxide, and fundamentally reduce the lithium loss and capacity loss caused by the irreversible reduction reaction of silicon oxide during the battery cycle, thereby correspondingly increasing the proportion of active silicon and the utilization rate of lithium and silicon in the battery cycle.

[0046] In the embodiment of the present application, silicon deposition and passivation treatment are carried out in the same generating equipment to avoid silicon oxidation self-ignition or material contamination during material transfer. That is, after the preparation of the silicon-carbon core is completed, inert gas is directly introduced into the silicon source gas pipeline for 30 minutes or more to replace the gas in the tube, and then an atmosphere containing carbon source gas is introduced for passivation treatment.

[0047] In the embodiment of the present application, the atmosphere containing the carbon source gas further includes a carrier gas, which is an inert gas.

[0048] In the embodiment of the present application, the inert gas may specifically be at least one of nitrogen and argon.

[0049] In the embodiment of the present application, the temperature of the passivation treatment is 450°C~650°C, for example, it can be but not limited to 450°C, 500°C, 550°C, 580°C, 600°C, and 650°C; the time of the passivation treatment is 2h~8h, for example, it can be but not limited to 2h, 3h, 3.5h, 4h, 5h, 6h, 7h, and 8h; the flow rate of the carbon source gas introduced during the passivation treatment is 2.5L / min~10L / min, for example, it can be but not limited to 2.5L / min, 4L / min, 5L / min, 6L / min, 8L / min, and 10 L / min; the flow rate of the carrier gas introduced during the passivation treatment is 1L / min~60L / min, for example, it can be but not limited to 40L / min, 45L / min, 50L / min, 55L / min, and 60L / min.

[0050] In an embodiment of the present application, the carbon source gas introduced during the passivation treatment includes one or more of olefins, alkynes, alcohols, and carbonates, such as, but not limited to, methane, ethane, propane, ethylene, propylene, acetylene, propyne, methanol, ethanol, propanol, dimethyl carbonate, ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, fluoroethylene carbonate, and mixtures thereof. In some specific embodiments of the present application, the carbon source gas introduced during the passivation treatment is preferably olefins and / or alkynes.

[0051] In the embodiment of the present application, the temperature of carbon deposition is 450°C to 650°C, such as but not limited to 450°C, 480°C, 500°C, 520°C, 550°C, 580°C, 600°C, 630°C, and 650°C; the time of carbon deposition is 0.5h to 8h, such as but not limited to 0.5h, 1h, 1.5h, 2h, 3h, 4h, 5h, 6h, 7h, and 8h. Carbon deposition deposits an initial carbon layer on the surface of the silicon-carbon core or the surface of the initial passivation layer, and the initial carbon layer completely covers the surface of the silicon-carbon core or the surface of the initial passivation layer.

[0052] In an embodiment of the present application, the carbon source gas introduced during the carbon deposition process includes one or more of alkanes, alkenes, and alkynes, such as, but not limited to, one or more of methane, ethane, propane, ethylene, propylene, acetylene, and propyne. In some embodiments of the present application, the flow rate of the carbon source gas introduced during the carbon deposition process is 1 L / min to 6 L / min, such as, but not limited to, 1 L / min, 2 L / min, 3 L / min, 4 L / min, 5 L / min, and 6 L / min; the flow rate of the carrier gas introduced during the carbon deposition process is 1 L / min to 60 L / min, such as, but not limited to, 1 L / min, 3 L / min, 5 L / min, 10 L / min, 15 L / min, 20 L / min, 25 L / min, 30 L / min, 40 L / min, 50 L / min, and 60 L / min.

[0053] In some specific embodiments of the present application, during the carbon deposition process, the temperature is 500°C~600°C, the time is 0.5h~5h, the flow rate of the carbon source gas is 2L / min~5L / min, and the flow rate of the carrier gas is 3L / min~30L / min.

[0054] The present application controls the deposition temperature, time, carbon source gas flow rate and carrier gas flow rate within the above ranges, so that the initial coating layer obtained by deposition has a suitable thickness and density. The deposition process combined with the subsequent heat treatment process can prepare a coating layer with a suitable thickness and suitable density, so that it has the technical effect of restricting the volume expansion of nano-silicon and facilitating lithium ion transmission. In step S102, the heat treatment is intended to moderately compress the interlayer voids and intralayer pores of the silicon-carbon core and the initial coating layer, thereby strengthening the overall wrapping strength of the initial coating layer on the silicon-carbon core, greatly reducing the activity space of the nano-silicon to inhibit its volume expansion, and strengthening the retention of the porous carbon substrate on the nano-silicon at the core level; the heat treatment also improves the uniformity and density of the initial coating layer, and constructs a shell with a suitable density for smooth insertion and extraction of lithium ions.

[0055] In an embodiment of the present application, the temperature is changed from the deposition temperature to the heat treatment temperature at a temperature ramp rate of 1°C / min to 15°C / min. The temperature ramp rate may be a heating rate or a cooling rate. In some embodiments of the present application, the temperature ramp rate may be, but is not limited to, 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, 11°C / min, 12°C / min, 13°C / min, 14°C / min, and 15°C / min. A gentle temperature ramp rate can avoid material cracking caused by thermal stress. In some specific embodiments of the present application, the temperature is changed from the deposition temperature to the heat treatment temperature at a temperature ramp rate of 5°C / min to 12°C / min.

[0056] In the embodiment of the present application, the heat treatment temperature is 400° C. to 750° C., for example, but not limited to, 400° C., 450° C., 500° C., 550° C., 600° C., 650° C., 700° C., and 750° C. If the heat treatment temperature is lower than 400° C., the heat provided is insufficient to change the density of the coating layer and the wrapping strength of the silicon-carbon core. If the heat treatment temperature is higher than 750° C., the silicon or carbon inside the silicon-carbon negative electrode material may crystallize, thereby reducing the theoretical capacity and cycle life of the battery. The embodiments of the present application limit the heat treatment to be carried out at 400℃~750℃, which can play a role in regulating the structure of the coating layer and the interaction between the layers. The mechanical strength of the coating layer in the silicon-carbon negative electrode material prepared at this temperature is high, and the wrapping strength of the silicon-carbon core is large, which can fully restrain the volume expansion of silicon and avoid the violent lithiation reaction of floating silicon, which directly affects the stability of the battery discharge process; at the same time, it avoids excessive high temperature to cause silicon particles to agglomerate and crystallize, thereby reducing the gram capacity of the silicon-carbon negative electrode material, and avoids carbon layer embrittlement or nano-silicon and carbon reaction to form silicon carbide crystals, thereby reducing the structural stability of the negative electrode material and the coulombic efficiency of the battery. In some embodiments of the present application, the temperature of the heat treatment is 400℃~700℃, which is more conducive to maintaining a smooth discharge reaction during the battery cycle to improve the cycle capacity stability of the battery. In some specific embodiments of the present application, the temperature of the heat treatment is 550℃~650℃, which can further coordinate battery performance and energy cost.

[0057] In the embodiments of the present application, the heat treatment time is 1h~6h, for example, it can be but not limited to 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h. The densification of the coating layer is gradually diffused from the outside to the inside. If the heat treatment time is less than 1h, the heat cannot fully penetrate the interior of the silicon-carbon negative electrode material, resulting in uneven densification and difficulty in fully achieving densification and strengthening of the coating layer. However, if the heat treatment time exceeds 6h, slow side reactions caused by long-term high temperature (such as local formation of silicon carbide) or excessive densification of the carbon layer may occur, hindering ion diffusion, thereby reducing the charge and discharge efficiency and capacity retention of the battery. The embodiments of the present application limit the heat treatment time to 1h~6h, which can achieve overall densification and moderate structural strengthening of the coating layer. In some embodiments of the present application, in accordance with the aforementioned temperature range, the heat treatment time is 1h~5h, which can achieve a comprehensive constraint and strengthening effect on the silicon-carbon core and reduce energy costs. In some specific embodiments of the present application, the heat treatment temperature is 550° C. to 650° C., and the heat treatment time is 1 h to 3 h, which has a better effect on improving the battery cycle performance.

[0058] In the embodiment of the present application, the heat treatment is performed under an inert atmosphere to avoid oxidative decomposition of silicon or carbon and ensure the structural integrity of the silicon-carbon negative electrode material.

[0059] In an embodiment of the present application, the silicon-carbon negative electrode material intermediate is subjected to heat treatment to obtain a silicon-carbon negative electrode material, and the initial coating layer of the silicon-carbon negative electrode material intermediate is converted into the coating layer of the silicon-carbon negative electrode material. Correspondingly, the initial passivation layer of the silicon-carbon negative electrode material intermediate is converted into the passivation layer of the silicon-carbon negative electrode material, and the initial carbon layer of the silicon-carbon negative electrode material intermediate is converted into the carbon layer of the silicon-carbon negative electrode material.

[0060] In the embodiment of the present application, the silicon-carbon negative electrode material intermediate is heat-treated at medium and low temperatures. First, for the silicon-carbon negative electrode material intermediate, the bonding strength between the layers can be improved, the gap between the coating layer and the silicon-carbon core is compressed, and the nano-silicon originally floating in the gap is firmly fixed, thereby limiting its free movement and volume expansion; secondly, for the shell layer, the medium and low temperature heat treatment can promote the shrinkage of the pores in the initial passivation layer and the initial carbon layer, and can also eliminate the surface functional groups in the initial carbon layer and the initial passivation layer, such as decomposing the carboxyl group and the hydroxyl group to escape in the form of CO / CO2 to reduce the defects of the carbon layer and break the carbon-hydrogen (CH) bond, thereby improving the uniformity and density of the initial carbon layer and the initial passivation layer, and further optimizing the confined space of the nano-silicon particles and the overall uniformity of the silicon-carbon negative electrode material; in addition, the medium and low temperature heat treatment can also make the amorphous carbon of the initial carbon layer locally sp 2Hybridization forms some graphite-like crystallites, which have higher electron mobility and higher carbon density than amorphous carbon, which helps to improve the conductivity of the material. At the same time, it is not enough to reach the level of graphitization, resulting in the carbon layer stacking being too dense and hindering ion diffusion.

[0061] In step S100, step S101 and step S102, the equipment for silicon deposition, passivation treatment, carbon deposition and heat treatment includes but is not limited to a fluidized bed, a rotary kiln or a kiln.

[0062] The embodiment of the present application provides a method for preparing a silicon-carbon negative electrode material, comprising coating and heat treating a silicon-carbon core, wherein the heat treatment improves the uniformity and density of the coating layer and enhances its wrapping strength on the silicon-carbon core. Preferably, a passivation treatment is added before carbon deposition to reduce the degree of oxidation of silicon. In the first cyclic voltammetry test of the silicon-carbon negative electrode material prepared by the preparation method, the discharge differential capacity curve presents a smooth lithiation platform rather than a steep step in the voltage range of 0.45V±0.05V, which means that there is less or no coulomb efficiency interference caused by floating silicon expansion or silicon oxide in the silicon-carbon negative electrode material, which promotes the silicon-carbon negative electrode material to undergo a smooth and stable discharge reaction, and helps to improve the capacity retention rate and cycle stability of the battery. In addition, the preparation method is simple and easy to implement, the process is coherent, and it is environmentally friendly and suitable for industrial production.

[0063] The embodiment of the present application provides a negative electrode plate, which includes a negative electrode current collector and a negative electrode active material layer provided on the surface of at least one side of the current collector, the negative electrode active material layer includes a silicon-carbon negative electrode material prepared by the aforementioned preparation method of the present application or the aforementioned silicon-carbon negative electrode material of the present application, other negative electrode active substances, a binder and a conductive agent. Among them, the negative electrode current collector is any current collector suitable for the negative electrode of the battery known in the art, and other negative electrode active substances include but are not limited to one or more of graphite, graphene, carbon nanotubes and carbon black. The binder and the conductive agent are also selected from materials familiar to those skilled in the art. The embodiment of the present application does not limit the mass proportion of the silicon-carbon negative electrode material in the negative electrode plate, and those skilled in the art can make a selection according to actual production needs.

[0064] The present application also provides a battery comprising a positive electrode plate and the aforementioned negative electrode plate. In some embodiments of the present application, the battery may be a liquid battery, a solid-state battery, or a semi-solid-state battery. In some embodiments of the present application, the battery may be an alkali metal ion battery such as a lithium-ion battery or a sodium-ion battery.

[0065] An embodiment of the present application also provides an electrical device, which includes the battery provided in the aforementioned embodiment of the present application. Since it is powered by the battery provided in the embodiment of the present application, the electrical device has good market competitiveness.

[0066] The technical solutions of the embodiments of the present application are described in detail below with reference to a number of embodiments. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commercially available products.

[0067] Example 1 1) Preparation of silicon carbon core: a porous carbon matrix (micropore porosity of 93.41%, mesopore porosity of 6.6%, crushing force of 14.97 mN, specific surface area of ​​2000 m 2 / g) was placed in a fluidized bed vapor deposition furnace, and nitrogen was introduced to replace the atmosphere in the reactor. The constant pressure was set at 6 kPa, the reaction temperature was 500°C, 60 L / min of nitrogen was introduced as a carrier gas, and 10 L / min of silane was introduced as a silicon source to deposit nano-silicon material. After the reaction lasted for 10 hours, the introduction of silane was stopped to obtain a silicon-carbon core.

[0068] 2) Preparation of a silicon-carbon anode material intermediate: Stop supplying silane and introduce nitrogen into the silicon source gas pipeline for 30 minutes to displace the silane. Then, introduce acetylene as the carbon source gas for passivation. The passivation temperature was set at 580°C, the nitrogen flow rate at 30 L / min, and the acetylene flow rate at 5 L / min. After 3.5 hours, an initial passivation layer formed on the silicon-carbon precursor. The precursor was then removed after cooling.

[0069] The cooled product of step 1) was placed in a rotary kiln and heated at room temperature for 1 h to 520°C. A mixture of acetylene and ethylene was introduced as a carbon source gas at a total gas rate of 3 L / min and a nitrogen flow rate of 3 L / min. The temperature was maintained at 520°C for 2 h to deposit an initial carbon layer to obtain a silicon-carbon negative electrode material intermediate.

[0070] 3) Preparation of silicon-carbon negative electrode material: Stop the introduction of carbon source gas, raise the furnace temperature to 700°C at a heating rate of 10°C / min, and heat treat the silicon-carbon negative electrode material intermediate in step 2) for 2 hours to obtain a silicon-carbon negative electrode material. The thickness of the coating layer in the silicon-carbon negative electrode material is 10 nm, and the mass percentage of silicon element is 60%.

[0071] Example 2 The only difference from Example 1 is that the heat treatment temperature in step 3) is 600°C.

[0072] Example 3 The only difference from Example 1 is that the heat treatment temperature in step 3) is 500°C.

[0073] Example 4 The only difference from Example 1 is that the heat treatment temperature in step 3) is 400°C.

[0074] Example 5 The only difference from Example 1 is that the heat treatment temperature in step 3) is 750°C.

[0075] Example 6 The only difference from Example 2 is that the heat treatment time in step 3) is 5 hours.

[0076] Example 7 The only difference from Example 1 is that the heat treatment temperature in step 3) is 400° C. and the time is 1 hour.

[0077] Example 8 The only difference from Example 1 is that the heat treatment temperature in step 3) is 750° C. and the time is 6 h.

[0078] Example 9 The only difference from Example 1 is that the passivation treatment time in step 1) is 2 hours.

[0079] Comparative Example 1 The only difference from Example 1 is that the temperature of the heat treatment in step 3) is 350°C.

[0080] Comparative Example 2 The only difference from Example 2 is that the heat treatment time in step 3) is 0.5 h.

[0081] Comparative Example 3 The only difference from Example 1 is that the heat treatment in step 4) is not performed, and the silicon-carbon negative electrode material intermediate is the silicon-carbon negative electrode material.

[0082] The following parameters were tested on the silicon-carbon negative electrode materials prepared in Examples 1 to 9 and Comparative Examples 1 to 3: Particle size D V 50 Detection: According to the particle size distribution laser diffraction method GB / T190772016, it is measured using Mastersizer 3000 laser diffraction technology.

[0083] Powder resistivity: Dry the silicon-carbon negative electrode material at 105°C for 2 hours to remove any moisture. Weigh the feeder and wipe it clean with dust-free paper dipped in alcohol. Place an appropriate amount of silicon-carbon negative electrode material in a powder resistance meter and output the powder resistance data under a pressure of 30 MPa.

[0084] The results of the above parameter tests are shown in Table 1: Table 1 Parameter test results of Examples 1 to 9 and Comparative Examples 1 to 3

[0085] The following performance tests were performed on the silicon-carbon negative electrode materials prepared in Examples 1 to 9 and Comparative Examples 1 to 3: To prepare a button-type half-cell, the silicon-carbon anode material was mixed with conductive carbon black (SP), carbon nanotubes (CNTs), and an aqueous binder consisting of lithium polyacrylate (PAAli) in a mass ratio of 85:9.8:0.2:5. This mixture was then prepared into a slurry with deionized water. The slurry was evenly coated on copper foil and vacuum-dried at 80°C for at least 2 hours. The electrode was punched out into small circular pieces using a punching machine, weighed, and then dried in a vacuum oven at 80°C for at least 6±0.5 hours. A lithium sheet was then used as the counter electrode, a lithium salt ester solution as the electrolyte, and a PE separator. The cells were assembled in a vacuum glove box to form a CR2016 button-type half-cell.

[0086] Preparation of a full battery: 12μm aluminum foil is used for coating the positive electrode, and 10μm copper foil is used for coating the negative electrode. Homogenization: Weigh the required materials and add them to a stirring kettle. Pre-mix the powder according to the predetermined process. After pre-mixing, add glue, stir and disperse, scrape the material, measure the viscosity, adjust the slurry state, vacuum, and sieve according to the predetermined process. Coating: Add the slurry to the material tank and start the coating machine to perform a trial coating. After the electrode is completely dried, take a sample for the first inspection and record the coating process record sheet. Test the coating surface density, coating thickness, coating length, coating gap length, etc. Once it meets the process requirements, start single-sided coating. After single-sided coating is completed, continue double-sided coating according to the single-sided coating process. Double-sided coating requires an additional coating alignment test. Pole slitting: According to the process size, use a cutter to cut the electrode coil into large pieces to be slit. Pole cold pressing: Cold pressing is first inspected. After confirming that the first inspection is qualified, batch cold pressing begins. Production: A double-needle electric welder is used for the negative electrode, and an ultrasonic spot welder is used for the positive electrode. After each electrode is spot welded, the weld status must be manually verified, and the designated locations must be covered with high-temperature adhesive as required. A winding machine is used to wind the battery cell. The battery cell is placed in the cut aluminum-plastic film, which is folded in half from the bottom to the top. After wrapping the core, it is clamped into the corresponding packaging mold (with the top flush and the top edge sealed). The mold is smoothly pushed into the mold cavity of the packaging machine. After the machine pops up, the mold is removed and the packaged battery is taken out. The package appearance and the tab spacing are confirmed to complete the top and side seals. The electrolyte is injected into the battery cell through the reserved injection port and weighed to confirm the injection volume. After injection, the battery cell is sealed using the sealing machine in the glove box. After confirming the sealing is complete, the battery cell is removed from the material channel.

[0087] Cyclic Voltammmetry (CV) testing method: Coin-cell batteries were tested using a BlueDian electrochemical station at 25°C. First, connect the electrodes to the BlueDian tester. Open the software and set the starting and ending potentials: a low potential of 0.05V, a high potential of 1.50V, a scan rate of 0.1mV / s, six scan segments, and a sampling interval of 0.001V. After completing the settings, click Start Test, wait for three cycles, and record the data.

[0088] Cycling performance testing method: Coin-type half-cells were tested using a Blue Electric electrochemical station at 25°C. The positive and negative tabs of the battery were clamped with a test charge and discharge fixture, and the test steps were set. 1. Wait for 10 minutes; 2. Charge at 1C CC / CV to 4.2V, then discharge at 0.05C; 3. Wait for 10 minutes; 4. Discharge at 1C CC to 3.0V; 5. Cycle steps 1-4 100 times; 6. End. Calculation method: Record the discharge capacity at step 3 as A1. Then, record the discharge capacity An at the 1C CC discharge to 3.0V step 100 cycles later. The capacity retention per week is calculated as An / A × 100%.

[0089] The results of the above performance tests are shown in Table 2: Table 2 Performance test results of Examples 1 to 9 and Comparative Examples 1 to 3

[0090] The only difference between Examples 2 to 5 and Comparative Example 1 and Example 1 is the temperature of the heat treatment. As can be seen from Table 1, the heat treatment can compress the interlayer gaps in the material and change the uniformity of the carbon material in the shell, so that the silicon-carbon negative electrode materials prepared respectively show differences in particle size and powder resistivity; as can be seen from Table 2, heat treatment within a certain temperature range can avoid or reduce the violent discharge reaction of the silicon-carbon negative electrode material in the voltage range of 0.45V±0.05V, which helps the discharge process to be smooth and stable, thereby improving the capacity retention rate of the battery.

[0091] The only difference between Example 6 and Comparative Example 2 and Example 2 is the heat treatment time. Table 2 shows that heat treatment with appropriate temperature and duration can promote a smooth discharge reaction of the silicon-carbon negative electrode material, thereby improving the cycle capacity stability of the battery.

[0092] Example 7 reflects a short-time heat treatment at low temperature, and Example 8 reflects a longer-time heat treatment at a higher temperature. As shown in Table 2, heat treatment with appropriate temperature and duration can optimize the smooth discharge reaction of the battery while avoiding changes in the silicon-carbon morphology of the silicon-carbon negative electrode material, thereby synergistically maintaining the battery's cycle capacity retention rate at a high level.

[0093] The difference between Comparative Example 3 and Example 2 is that no heat treatment is performed. Figure 3 This is a differential capacity curve diagram of the first cyclic voltammetry test of the silicon-carbon negative electrode material prepared in Example 2 of the present application, where L1 is the discharge differential capacity (dQ / dV) curve, Figure 4This is a graph showing the differential capacity curve from the first cyclic voltammetry test of the silicon-carbon anode material prepared in Comparative Example 3 of this application, where L2 is the discharge differential capacity (dQ / dV) curve. Comparing L1 and L2, it can be seen that heat treatment directly affects the peak value and rate of change of the discharge differential capacity of the silicon-carbon anode material in the voltage range of 0.45V±0.05V, thereby promoting a smooth and stable discharge process for the silicon-carbon anode material during battery cycling.

[0094] The only difference between Example 9 and Example 1 is the degree of passivation treatment. As can be seen from Tables 1 and 2, the passivation treatment also has a certain positive effect on reducing the discharge differential capacity peak and change rate of the silicon-carbon negative electrode material in the voltage range of 0.45V±0.05V, and can cooperate with heat treatment to improve the comprehensive stability of the silicon-carbon negative electrode material in the battery cycle.

[0095] In summary, the silicon-carbon negative electrode material provided in the embodiments of the present application is obtained by heat treating the coated silicon-carbon core. The silicon-carbon negative electrode material can effectively avoid capacity decay caused by silicon expansion or silicon oxide side reactions during battery cycling. The discharge differential capacity curve of the first cyclic voltammetry test presents a uniform and smooth platform in the voltage range of 0.45V±0.05V, which helps to promote a smooth and stable discharge process of the battery and improve the capacity retention and cycle stability of the battery after multiple cycles.

[0096] The above disclosure is only a preferred embodiment of the present application and cannot be used to limit the scope of rights of the present application. Ordinary technicians in this field can understand that all or part of the processes of the above embodiments and equivalent changes made in accordance with the claims of the present application are still within the scope covered by the present application.

Claims

1. A silicon-carbon negative electrode material, characterized in that: It comprises a silicon-carbon core and a coating layer covering the silicon-carbon core, wherein the silicon-carbon core comprises a porous carbon substrate and nano-silicon arranged on the porous carbon substrate; The test result of the first cyclic voltammetry test of the silicon-carbon negative electrode material meets at least one of the following conditions: (a) The discharge differential capacity curve has a value of dQ / (dV×C) less than or equal to 1.7 in the voltage range of 0.45V±0.05V. dQ / dV represents the differential capacity in mAh / V, and C represents the charge capacity in mAh. (b) The discharge differential capacity curve has no sharp peak in the voltage range of 0.45V±0.05V.

2. The silicon-carbon negative electrode material according to claim 1, wherein In the first cyclic voltammetry test of the silicon-carbon negative electrode material, the discharge capacity in the voltage range of 0.45V±0.05V accounts for less than or equal to 4% of the total discharge capacity.

3. The silicon-carbon negative electrode material according to claim 1, wherein The silicon-carbon negative electrode material satisfies at least one of the following conditions: (a) Particle size D of the silicon-carbon negative electrode material V 50 is 5μm~10μm; (b) The mass percentage of silicon element in the silicon-carbon negative electrode material is 40% to 75%; (c) the powder resistivity of the silicon-carbon negative electrode material under a test pressure of 30 MPa is less than or equal to 10 Ω·cm; (d) In the silicon-carbon negative electrode material, the coating layer has a thickness of 1 nm to 100 nm.

4. A method for preparing the silicon-carbon negative electrode material according to any one of claims 1 to 3, characterized in that: include: Placing the silicon-carbon core in an atmosphere containing a carbon source gas for deposition to obtain a silicon-carbon negative electrode material intermediate; The silicon-carbon negative electrode material intermediate is heat-treated to obtain a silicon-carbon negative electrode material. The heat treatment temperature is 400° C. to 750° C., and the heat treatment time is 1 hour to 6 hours.

5. The method for preparing the silicon-carbon negative electrode material according to claim 4, wherein: The deposition temperature is 450° C. to 650° C., and the deposition time is 0.5 h to 16 h.

6. The method for preparing the silicon-carbon negative electrode material according to claim 4, wherein: The atmosphere containing the carbon source gas also includes a carrier gas. During the deposition, the flow rate of the carbon source gas is 1 L / min to 10 L / min, and the flow rate of the carrier gas is 1 L / min to 60 L / min. The carbon source gas includes one or more of alkanes, alkenes, alkynes, alcohols and carbonates.

7. The method for preparing the silicon-carbon negative electrode material according to claim 4, wherein: The preparation of the silicon-carbon core comprises: placing a porous carbon substrate in an atmosphere containing a silicon source gas to perform silicon deposition to obtain the silicon-carbon core; The silicon source gas-containing atmosphere further includes an initial carrier gas. During the silicon deposition, the flow rate of the silicon source gas is 5 L / min to 10 L / min, and the flow rate of the initial carrier gas is 40 L / min to 60 L / min. The silicon source gas includes one or more of monosilane, disilane and chlorosilane.

8. The method for preparing the silicon-carbon negative electrode material according to claim 7, wherein: The silicon deposition temperature is 500° C. to 600° C., the pressure is 2 KPa to 10 KPa, and the time is 8 h to 30 h.

9. A negative electrode plate, characterized in that: The invention comprises a negative electrode current collector and a negative electrode active material layer arranged on at least one side of the negative electrode current collector, wherein the negative electrode active material layer comprises the silicon-carbon negative electrode material according to any one of claims 1 to 3 or the silicon-carbon negative electrode material prepared by the preparation method according to any one of claims 4 to 8.

10. A battery, characterized in that: It comprises a positive electrode sheet and the negative electrode sheet as claimed in claim 9.

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