Negative electrode material and preparation method thereof, battery monomer, battery and electric device

Abstract

The invention discloses a negative electrode material and a preparation method thereof, a battery monomer, a battery and an electric device. The negative electrode material comprises silicon carbon particles and a coating layer, the coating layer comprises graphene and a polymer, and the surface of the silicon carbon particles is at least partially coated with the coating layer. According to the negative electrode material provided by the embodiment of the invention, the battery monomer has relatively high cycle performance and relatively long service life at the same time, and the battery comprising the battery monomer and the electric device at least have the same advantages.

Description

Technical Field

[0001] This application belongs to the technical field of energy storage devices, and particularly relates to a negative electrode material, a preparation method thereof, a battery cell, a battery, and an electrical device. Background Art

[0002] In recent years, due to the higher requirements for energy density in the electric vehicle industry, a large amount of research has been carried out on high-capacity negative electrode materials. Negative electrode materials include graphite, mesophase carbon microspheres, soft carbon, hard carbon, lithium titanate, silicon-carbon composite materials, etc.

[0003] Silicon-carbon materials have a high theoretical specific capacity, several times that of graphite materials, and thus have received attention. However, silicon-carbon materials have a serious volume effect, generating a huge volume expansion during the charging process and being prone to pulverization, resulting in a relatively fast capacity decay of the battery and poor cycle performance.

[0004] Based on this, this application is specifically proposed. Summary of the Invention

[0005] This application provides a negative electrode material, a preparation method thereof, a battery cell, a battery, and an electrical device, aiming to enable the battery cell to simultaneously have relatively high cycle performance and service life.

[0006] In the first aspect of the embodiments of this application, a negative electrode material is provided, including:

[0007] Silicon-carbon particles, and

[0008] A coating layer, including graphene and a polymer; the coating layer at least partially coats the surface of the silicon-carbon particles,

[0009] According to the embodiments of this application, the coating layer is disposed on the surface of the silicon-carbon particles, restricting the volume change of the silicon-carbon particles, reducing the overall volume change of the negative electrode material, improving the stability of the solid electrolyte interface film (SEI) on the surface of the negative electrode sheet, so that the solid electrolyte interface film will not be repeatedly formed and broken due to the large volume change of the silicon-carbon particles in the negative electrode material, avoiding the further consumption of active ions for forming the SEI film, and stabilizing the conduction path of the active ions; it also improves the stability of each component in the electrolyte and reduces the influence on the electrolyte components; thereby improving the cycle performance of the battery.

[0010] According to the embodiments of this application, a certain amount of polymer is included in the coating layer of the negative electrode material, improving the stability and firmness of the coating layer, hindering the pulverization of the negative electrode material due to volume change and complex stress during charge and discharge, improving the close contact between the negative electrode material, the conductive agent, and the binder, thereby improving the conductivity of the negative electrode sheet containing the negative electrode material and improving the fast charge and discharge performance of the battery. The coating layer having a polymer can improve the elasticity and toughness of the coating layer and better protect the silicon-carbon particles.

[0011] According to the embodiments of the present application, the coating layer of the negative electrode material contains graphene, which improves the conductivity of the coating layer, thereby improving the fast charge and discharge performance of the battery. The coating layer with higher conductivity enhances the electron conduction performance of the negative electrode material, thereby improving the capacity utilization of the negative electrode material and the capacity retention rate during cycling. It can also inhibit the increase in impedance of the battery cell during the charge and discharge cycle, reduce battery polarization, and improve the cycling performance of the battery cell.

[0012] In some optional embodiments, during the process of heating the coating layer from 25 °C to 800 °C in an inert non-oxidizing gas atmosphere, the weight loss rate of the coating layer is 0.1% - 3.5%, and can be optionally 0.5% - 2%.

[0013] According to the embodiments of the present application, the weight loss rate of the coating layer within the above range indicates that the coating layer can be further carbonized, which can characterize the presence of polymers and possible intermediate products in the negative electrode material, is beneficial to improving the firmness between the coating layer and the silicon-carbon particles, and indicates that the negative electrode material has a suitable range that allows volume changes of the silicon-carbon particles in the negative electrode material while having the stability of the coating layer; on the other hand, it also reflects the degree of carbonization of the coating layer, indicating how many sites can intercalate and deintercalate active ions in this layer, and to a certain extent reflects an increase in the specific capacity of the negative electrode material.

[0014] In some optional embodiments, based on the total mass of the negative electrode material, the negative electrode material includes 0.1% - 5% of the coating layer.

[0015] According to the embodiments of the present application, the mass content of the coating layer in the negative electrode material within the above range limits the volume change of the silicon-carbon particles, reduces the overall volume change of the negative electrode material, improves the stability of the solid electrolyte interface film (SEI) on the surface of the negative electrode sheet, prevents the solid electrolyte interface film from being repeatedly formed and broken due to large volume changes of the silicon-carbon particles in the negative electrode material, avoids further consumption of active ions by the formation of the SEI film, and stabilizes the conduction path of active ions; it also improves the stability of each component in the electrolyte and reduces the impact on the electrolyte components; thereby improving the cycling performance of the battery.

[0016] In addition, the mass content of the coating layer in the negative electrode material within the above range is beneficial to the intercalation and deintercalation of active ions such as lithium ions in the negative electrode material, and is beneficial to the charge and discharge performance of the negative electrode material.

[0017] In some optional embodiments, the polymer includes one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyethyleneimine, polyetheretherketone, and copolymers of ethylene and tetrafluoroethylene.

[0018] According to the embodiments of the present application, polymers of the above types can improve the stability and firmness of the coating layer, prevent the pulverization of the negative electrode material due to volume changes and complex stress during charge and discharge processes, enhance the close contact between the negative electrode material, the conductive agent, and the binder, thereby improving the conductivity of the negative electrode sheet containing the negative electrode material and enhancing the fast charge and discharge performance of the battery. The coating layer contains polymers, which can improve the elasticity and toughness of the coating layer and better protect the silicon-carbon particles.

[0019] In some alternative embodiments, the coating layer contains intermediate products. Optionally, the intermediate products contain one or more of fluorine element, nitrogen element, and oxygen element.

[0020] According to the embodiments of the present application, the intermediate products can be understood as the intermediate products formed during the carbonization process of the polymers. It indicates that the coating layer of the negative electrode material is prepared by in-situ carbonization of the polymers. Therefore, it can be shown that the coating layer has better stability and is not easily detached and pulverized. The intermediate products contain one or more of fluorine element, nitrogen element, and oxygen element, indicating that the carbonization of the polymers into graphene or amorphous carbon is not complete, and some fluorine element, nitrogen element, and oxygen element remain and can continue to be carbonized.

[0021] In some alternative embodiments, the average number of layers Dn80 of graphene ≤ 3, and it can be selected as 1 - 2.

[0022] According to the embodiments of the present application, graphene is an excellent conductive material. The coating layer containing graphene with the above mass content can improve the conductivity of the coating layer, thereby enhancing the fast charge and discharge performance; graphene has excellent mechanical strength and wear resistance, and it can enhance the hardness and durability of the coating layer; graphene has high thermal conductivity, so the heat generated when the coating layer inserts and extracts active ions can be better conducted, which is beneficial to improving the thermal conductivity performance of the coating layer.

[0023] According to the embodiments of the present application, the coating layer contains graphene with the above characteristics or types, indicating that graphene has good quality, which is beneficial to improving the conductivity of the negative electrode material and the performance of inserting and extracting active ions.

[0024] In some alternative embodiments, the coating layer includes amorphous carbon.

[0025] According to the embodiments of the present application, the presence of amorphous carbon in the coating layer can increase the sites for inserting and extracting active ions, further improving the specific capacity of the negative electrode material. The amorphous carbon, together with the polymers and graphene in the coating layer, improves the stability of the coating layer, making the coating layer not easily detached and pulverized.

[0026] In some alternative embodiments, the average particle size Dv of the silicon-carbon particles 150 is 5 μm to 20 μm, and may be 5 μm to 10 μm.

[0027] According to an embodiment of the present application, the average particle size Dv of the silicon-carbon particles is controlled 1 When 50 is within the above range, it is beneficial to control the overall particle size of the negative electrode material, beneficial to the deposition and insertion / extraction of active ions of the negative electrode material, and to improve the electron transport performance of the negative electrode material, and can also reduce the side reactions of the electrolyte at the negative electrode.

[0028] In some alternative embodiments, the silicon-carbon particles include 65% to 78% of silicon element and 22% to 35% of carbon element by mass percentage.

[0029] According to an embodiment of the present application, controlling the elements of the silicon-carbon particles to have the above mass fractions is beneficial to controlling the overall volume change rate of the silicon-carbon particles during the electrochemical cycle of the battery, beneficial to improving the stability of the coating layer and the specific capacity of the negative electrode material.

[0030] In some alternative embodiments, the negative electrode material is granular. In some alternative embodiments, the average particle size Dv of the negative electrode material 2 50 is 5.05 μm to 25 μm, and may be 5.5 μm to 10.5 μm.

[0031] According to an embodiment of the present application, the negative electrode material having an appropriate volume average particle size Dv50 is beneficial to improving the powder compaction density of the negative electrode material itself, so that the negative electrode has a high specific capacity. Using this negative electrode material can make the compaction density of the electrode sheet higher and can reduce the addition amount of the binder in the negative electrode sheet, thereby improving the energy density of the battery.

[0032] In some alternative embodiments, the specific surface area of the negative electrode material is 2 m 2 / g to 30 m 2 / g, and may be 3 m 2 / g to 20 m 2 / g.

[0033] According to an embodiment of the present application, by controlling the specific surface area of the negative electrode material within the above range, more active sites can be provided for the insertion / extraction of active ions including lithium ions by the negative electrode material, the specific capacity of the negative electrode material can be improved; it is also beneficial to reduce the side reactions of the electrolyte at the negative electrode, and can also reduce the film formation consumption of active ions at the negative electrode, thereby improving the cycle performance of the battery.

[0034] In some alternative embodiments, the intensity I of the D peak in the Raman spectrum of the negative electrode material D and the intensity I of the G peak G The ratio I D / I G is 1 to 2.5, and may be 1.2 to 2, wherein the D peak is located at 1340 cm-1 ~1360 cm -1 at a position of, the G peak is at 1570 cm -1 ~1590 cm -1 at a position of.

[0035] The peak intensity I of the D peak D and the peak intensity I of the G peak G The ratio within the above range can reduce the irreversible capacity of the negative electrode material during charge and discharge cycles, while ensuring that the coating layer has excellent electrical conductivity, which is beneficial to the capacity performance of the negative electrode material, improving the cycle capacity retention rate of the negative electrode material, and thus improving the first Coulomb efficiency, cycle performance, and energy density of the battery cells using such negative electrode materials.

[0036] In a second aspect, the embodiments of the present application provide a method for preparing a negative electrode material, the method including:

[0037] Providing silicon-carbon particles coated with a polymer emulsion;

[0038] Using laser to treat the silicon-carbon particles coated with the polymer emulsion so that at least part of the polymers in the polymer emulsion are carbonized and graphitized to form a coating layer, obtaining the negative electrode material of the first aspect, wherein the coating layer includes graphene and polymers.

[0039] According to the preparation method of the embodiments of the present application, by in-situ preparing a carbonized and graphitized coating layer, and the coating layer contains a certain amount of polymers, the stability and firmness of the coating layer are improved, preventing the pulverization of the negative electrode material due to volume change and complex stress during charge and discharge, improving the close contact between the negative electrode material, the conductive agent, and the binder, thereby improving the electrical conductivity of the negative electrode sheet containing the negative electrode material and the fast charge and discharge performance of the battery.

[0040] According to the embodiments of the present application, using laser to treat the silicon-carbon particles coated with the polymer emulsion can make the coating layer possibly contain intermediate products in different states during the carbonization of the polymers. On the one hand, this intermediate product can reflect the stability degree of the coating layer, making the coating layer of the negative electrode material have a certain stability, enabling a certain close contact between the negative electrode material, the conductive agent, and the binder, and allowing the volume change of the silicon-carbon particles in the negative electrode material to have a suitable range.

[0041] In some optional embodiments, the method satisfies at least one of the following conditions:

[0042] 1) The laser type is a carbon dioxide laser;

[0043] 2) The power during laser treatment is 10 W - 150 W;

[0044] 3) The scanning rate of the laser treatment is 0.01 m / s to 2 m / s;

[0045] 4) The time interval of the laser treatment is 0.1 s to 1 s.

[0046] According to the embodiments of the present application, by regulating one or more of the above process conditions, the above-mentioned negative electrode material can be prepared.

[0047] In some alternative embodiments, the polymer emulsion includes a first polymer and a second polymer, and the mass ratio of the first polymer to the second polymer is 1:(0.01 - 2).

[0048] According to the embodiments of the present application, by controlling the mass ratio of the first polymer to the second polymer within the above range, graphene is formed by the first polymer in the polymer emulsion. The second polymer has good heat resistance, excellent chemical corrosion resistance of the material itself, and good creep resistance. They can also be used as binders for active materials. More importantly, the carbonized parts of these polymers provide carbon sites and the remaining second polymer forms a three-dimensional network structure, which can coat the silicon-carbon particles to control the expansion of their size, and at the same time can also play a role in fixing the graphene material formed by the first polymer.

[0049] In some alternative embodiments, the first polymer includes one or more of chitosan, chitin, and cellulose. In some alternative embodiments, the second polymer includes one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyethyleneimine, polyether ether ketone, and a copolymer formed by ethylene and tetrafluoroethylene. According to the embodiments of the present application, the coating layer is composed of the above two polymers, which is beneficial to improving the stability of the coating layer and the comprehensive performance of the battery.

[0050] In a third aspect, the embodiments of the present application provide a negative electrode tab, which includes a negative electrode current collector and a negative electrode active material film layer disposed on at least one side of the negative electrode current collector. The negative electrode active material film layer includes the negative electrode material of the first aspect or the negative electrode material prepared by the preparation method of the second aspect. Therefore, the negative electrode tab of the present application has at least the beneficial effects included in the negative electrode material.

[0051] In a fourth aspect, the embodiments of the present application provide a battery cell, which includes the negative electrode tab of the third aspect.

[0052] In a fifth aspect, the embodiments of the present application provide a battery, which includes the battery cell of the fourth aspect.

[0053] In a sixth aspect, the embodiments of the present application provide an electrical device, which includes the battery of the fifth aspect.

[0054] The battery cell, battery, and electrical device of the present application include the negative electrode material of the first aspect of the present application, or the negative electrode material prepared by the preparation method of the second aspect, or the negative electrode sheet of the third aspect, and thus at least have the same advantages as those of the application of the negative electrode sheet. Description of the Drawings

[0055] Figure 1 A schematic diagram showing an embodiment of the battery cell of the present application is shown.

[0056] Figure 2 Shows the present application Figure 2 exploded view.

[0057] Figure 3 A schematic diagram showing an embodiment of the battery module of the present application is shown.

[0058] Figure 4 A schematic diagram showing an embodiment of the battery pack of the present application is shown.

[0059] Figure 5 Shows the present application Figure 4 exploded view.

[0060] Figure 6 A schematic diagram showing an embodiment of the device using the battery cell of the present application as a power source is shown. Detailed Embodiments

[0061] In order to make the invention purpose, technical solution, and beneficial technical effects of the present application clearer, the present application will be described in detail below with reference to specific embodiments. It should be understood that the embodiments described in this specification are only for explaining the present application and not for limiting the present application.

[0062] For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recorded; and any lower limit can be combined with other lower limits to form a range not explicitly recorded, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recorded. In addition, although not explicitly recorded, each point or single value between the range endpoints is included in this range. Thus, each point or single value can be used as its own lower limit or upper limit and combined with any other point or single value or combined with other lower limits or upper limits to form a range not explicitly recorded.

[0063] In the description herein, it should be noted that unless otherwise specified, "above" and "below" include this number, and the meaning of "one or several" in "one or several" is two or more.

[0064] The above - mentioned invention content of this application does not intend to describe every disclosed embodiment or every implementation mode in this application. The following description more specifically illustrates exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments, which can be used in various combinations. In each embodiment, the enumeration is only a representative group and should not be construed as exhaustive.

[0065] Silicon - carbon materials have a high theoretical lithium - storage capacity (generally 4200 mAh / g) and a relatively low lithium - deintercalation voltage platform (0.5 V), and are one of the very promising anode materials for batteries. However, during the charge - discharge process of the battery, the volume expansion rate of silicon - carbon materials reaches 300% - 400%, and there are serious interfacial side reactions, which hinder their practical applications.

[0066] In addition, the high internal stress of silicon - carbon materials easily causes the pulverization of silicon particles. The pulverization of particles and continuous expansion - contraction will cause the repeated formation and rupture of the solid electrolyte interface film (SEI), consuming the limited electrolyte inside the battery, which is not conducive to the cycle performance and service life of the battery. Moreover, the continuous expansion - contraction of silicon - carbon materials during the charge - discharge process of the battery will cause the contact between the anode active material, the conductive agent, and the binder to deteriorate, thus affecting the conductivity and the cycle performance and kinetic performance of the battery.

[0067] In view of this, the embodiments of this application provide an anode material that has a coating layer containing a carbon - based material and a polymer on the surface of silicon - carbon particles. A battery containing this anode material can obtain improved cycle performance, service life, and kinetic performance.

[0068] Negative electrode material

[0069] The first aspect of the embodiments of this application provides an anode material, including:

[0070] Silicon - carbon particles, and

[0071] A coating layer, including graphene and a polymer, and the coating layer at least partially coats the surface of the silicon - carbon particles.

[0072] According to the embodiments of this application, the coating layer is disposed on the surface of the silicon - carbon particles, restricting the volume change of the silicon - carbon particles, reducing the overall volume change of the anode material, improving the stability of the solid electrolyte interface film (SEI) on the surface of the anode electrode sheet, so that the solid electrolyte interface film will not be repeatedly formed and ruptured due to the large volume change of the silicon - carbon particles in the anode material, avoiding the further consumption of active ions by forming the SEI film, and stabilizing the conduction path of active ions; it also improves the stability of each component in the electrolyte and reduces the influence on the electrolyte components; thus improving the cycle performance of the battery.

[0073] According to the embodiments of the present application, the coating layer in the negative electrode material contains a certain amount of polymer, which improves the stability and firmness of the coating layer, hinders the pulverization of the negative electrode material due to volume change and complex stress during charge and discharge, improves the close contact between the negative electrode material, the conductive agent and the binder, thereby improving the conductivity of the negative electrode sheet containing the negative electrode material, and improving the fast charge and discharge performance of the battery. The coating layer having a polymer can improve the elasticity and toughness of the coating layer and better protect the silicon-carbon particles.

[0074] According to the embodiments of the present application, the coating layer of the negative electrode material contains graphene, which improves the conductivity of the coating layer, thereby improving the fast charge and discharge performance of the battery. The coating layer with higher conductivity improves the electron conduction performance of the negative electrode material, thereby improving the capacity utilization of the negative electrode material and the capacity retention rate during cycling, and can also inhibit the increase in impedance of the battery cell during charge and discharge cycling, reduce battery polarization, and improve the cycling performance of the battery cell.

[0075] As an example, when characterizing the negative electrode material using infrared spectroscopy, when there is an infrared absorption peak in the infrared spectrum at around 1220 cm -1 it belongs to the asymmetric stretching vibration mode (VasCF2) of the F-C-F in polytetrafluoroethylene, while the infrared absorption peak at around 1150 cm -1 belongs to the symmetric stretching vibration mode (VsCF2) of the F-C-F in polytetrafluoroethylene. For example, in the infrared spectrum, there is a vibration peak of the carbon-carbon double bond skeleton at around 1550 cm -1 which can belong to graphene.

[0076] The infrared spectrum analysis of the negative electrode material can be carried out by using the instruments and methods well-known in the art, such as an infrared spectrometer, such as the IS10 type Fourier transform infrared spectrometer of Nicolet company in the United States, and the infrared spectrum of the negative electrode material of the present application is tested according to the general rules of infrared spectrum analysis method GB / T6040-2002.

[0077] In some alternative embodiments, based on the total mass of the negative electrode material, the negative electrode material includes 0.1% to 5% of the coating layer.

[0078] Optionally, the negative electrode material includes 0.1%, 0.05%, 0.1%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, 1%, 2%, 3%, 4%, 5% of any value or the range composed of them as the coating layer.

[0079] According to the embodiments of the present application, when the mass content of the coating layer in the negative electrode material is within the above range, it is beneficial to the insertion and extraction of active ions such as lithium ions in the negative electrode material, and is beneficial to the charge-discharge performance of the negative electrode material.

[0080] The mass content of the coating layer in the negative electrode material can be detected by stripping the coating layer. As an example, a certain amount of the coated negative electrode material is weighed and recorded as M1. Then, the negative electrode material is placed in a mixed solution of water and ethanol, where the volume ratio of water to ethanol is 1:1, and the mass ratio of the negative electrode material to the mixed solution is 1:10. The mixed solution containing the negative electrode material is ultrasonically treated for 20 - 40 min, and the ultrasonic frequency is 20 - 40 HZ, which can be 25 HZ. Then, it is washed and filtered, and the silicon-carbon particles are collected. After drying, the collected silicon-carbon particles are weighed and recorded as M2. Next, the silicon-carbon particle negative electrode material with the mass of M2 collected is continued to be placed in the mixed solution of water and ethanol, and ultrasonically treated for 20 - 40 min again. Then, it is washed, filtered, and separated to collect the silicon-carbon particles and the powder material of the coating layer. After drying, the collected silicon-carbon particles are weighed and recorded as M3. When the mass change between M2 and M3 is < 0.2%, it indicates that the coating layer on the surface of the silicon-carbon material has been stripped clean. The content m of the coating layer is measured as m = M1 - M3. In some embodiments, vacuum filtration separation can be used for filtration separation. The mesh aperture for separating the silicon-carbon particles and the powder material of the coating layer can be 0.45 μm to 0.7 μm, and can be optionally 0.55 μm.

[0081] In some alternative embodiments, during the process of heating from 25°C to 800°C in an inert non-oxidizing gas atmosphere, the weight loss rate of the coating layer is 0.1% - 3.5%.

[0082] In some embodiments, during the process of heating from 25°C to 800°C in an inert non-oxidizing gas atmosphere, the weight loss rate of the coating layer can be any value among 0.1%, 0.5%, 0.8%, 1%, 1.5%, 1.8%, 2.0%, 2.5%, 3.0%, 3.5% or the range composed of them.

[0083] According to the embodiments of the present application, when the weight loss rate of the coating layer is within the above range, it indicates that the coating layer can be further carbonized, which can characterize the presence of polymers and possible intermediate products in the negative electrode material, is beneficial to improving the firmness between the coating layer and the silicon-carbon particles, and indicates that the negative electrode material has a suitable range for allowing volume changes of the silicon-carbon particles in the negative electrode material while having the stability of the coating layer; on the other hand, it also reflects the degree of carbonization of the coating layer, indicating how many sites for inserting and extracting active ions the layer has, and to a certain extent, reflects an increase in the specific capacity of the negative electrode material.

[0084] The above detection method of the weight loss rate includes: separating the coated powder material from the negative electrode material, and the weight loss rate of the coated powder material when heated from 25°C to 800°C in an inert non-oxidizing gas atmosphere can characterize the amount of the coating layer with the above polymers and possible intermediate products. In some embodiments, during the process of heating from 25°C to 800°C in an inert non-oxidizing gas atmosphere, the weight loss rate of the coating layer is 0.25% - 0.84%. Optionally, during the process of heating from 25°C to 800°C in an inert non-oxidizing gas atmosphere, the weight loss rate of the coating layer is 0.3% - 1.5%, more preferably 0.45% - 1.2%.

[0085] The selection of the inert non-oxidizing gas is not particularly critical as long as it does not substantially affect the structure of the coating layer. Examples of the inert non-oxidizing gas include, but are not limited to, nitrogen, carbon dioxide, ammonia, and inert gases (e.g., helium, argon), as well as combinations thereof. In some preferred embodiments, nitrogen can be used as the inert non-oxidizing gas.

[0086] Based on the present application, those skilled in the art can reasonably determine the heating rate during the weight loss process. For example, the heating rate during the weight loss process can be 10°C / min or lower, preferably 5°C / min or lower. In an exemplary embodiment, the weight loss rate is measured during the process of heating from 25°C to 800°C at a rate of 10°C / min in an inert non-oxidizing gas (e.g., nitrogen) atmosphere.

[0087] In some alternative embodiments, the polymer includes one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyethyleneimine, polyetheretherketone, and copolymers of ethylene-tetrafluoroethylene.

[0088] According to the embodiments of the present application, polymers of the above types can improve the stability and firmness of the coating layer, prevent the pulverization of the negative electrode material due to volume change and complex stress during charge and discharge processes, improve the close contact between the negative electrode material, the conductive agent, and the binder, thereby improving the conductivity of the negative electrode sheet containing the negative electrode material and the fast charge and discharge performance of the battery. The coating layer has polymers, on the one hand, which can allow the internal silicon-carbon particles to have a relatively large volume change rate, maintain the stability of the coating layer and have a certain elastic deformation ability, improve the elasticity and toughness of the coating layer, and improve the stability of the negative electrode material.

[0089] In some alternative embodiments, the coating layer contains intermediate products. Optionally, the intermediate products contain one or more of fluorine element, nitrogen element, and oxygen element.

[0090] According to the embodiments of the present application, the intermediate product can be understood as the intermediate product formed during the carbonization of the polymer, indicating that the coating layer of the negative electrode material is prepared by in-situ carbonization of the polymer. The intermediate product is not completely carbonized during the polymer carbonization process and contains other non-carbon elements. Therefore, it can be shown that the coating layer has better stability and is not easily peeled off and pulverized. The intermediate product contains one or several of fluorine element, nitrogen element, and oxygen element, and these elements come from the raw materials (polymers) used in the preparation, indicating that the carbonization of the polymer into graphene or amorphous carbon is not complete, and some fluorine element, nitrogen element, and oxygen element remain and can continue to be carbonized.

[0091] The detection method of the intermediate product can include: taking a coating layer sample, dispersing the coating layer sample in a solvent, and removing most of the polymer, graphene, and amorphous carbon by performing infrared spectroscopy analysis. By further infrared spectroscopy analysis, it is found that any one of the carbon-fluorine bond, carbon-oxygen bond, and carbon-nitrogen bond different from the polymer is present. It can be considered that the intermediate product has been measured. As an example, in the infrared spectrum, there is an F -1 C=C characteristic peak near the position of 1719 cm 2 , indicating that an intermediate product containing F atoms has been prepared. As an example, in the infrared spectrum, there is an O=C characteristic peak near the position of 1720 cm -1 , indicating that an intermediate product containing O atoms has been prepared. As an example, in the infrared spectrum, there is a carbon-nitrogen characteristic peak near the position of 2205 cm -1 , indicating that an intermediate product containing N atoms has been prepared.

[0092] In some alternative embodiments, the average number of layers Dn80 of graphene is ≤ 3, and can be selected as 1 - 2.

[0093] Graphene is an excellent conductive material. The coating layer containing graphene with the above mass content can improve the conductivity of the coating layer, thereby improving the fast charge and discharge performance; graphene has excellent mechanical strength and wear resistance, and it can enhance the hardness and durability of the coating layer; graphene has high thermal conductivity, so the heat generated when the coating layer inserts and extracts active ions can be better conducted, which is beneficial to improving the thermal conductivity performance of the coating layer. On the other hand, the coating layer including graphene with the above content improves the conductivity of the negative electrode material, and also provides additional insertion and extraction sites for active ions for the negative electrode material, increasing the specific capacity of the negative electrode material, thereby reducing the energy density of the battery.

[0094] The average number of layers Dn80 of graphene represents the number of layers corresponding to 80% of the number distribution of graphene, and can be measured by well-known instruments and methods in the art. For example, sampling detection is performed using Raman spectroscopy or atomic force microscopy.

[0095] As an example, the Raman spectrum of graphene consists of several peaks, mainly the G peak, D peak, and G' peak.

[0096] The G peak is the main characteristic peak of graphene, which is caused by the in-plane vibration of sp2 carbon atoms and appears at around 1580 cm-1. This peak can effectively reflect the number of layers of graphene. For example, the typical Raman spectrum of single-layer graphene excited by a 514.5 nm laser. Its corresponding characteristic peaks are located at the G peak near 1582 cm-1 and the G' peak near 2700 cm-1. If there are more edges or defects in graphene, a D peak at around 1350 cm-1 and a D' peak at around 1620 cm-1 will also appear. 1 According to the embodiments of the present application, the coating layer contains graphene with the above characteristics or types, indicating that graphene has good quality, which is beneficial to improving the conductivity of the negative electrode material and the performance of intercalating and deintercalating active ions. -1 In some optional embodiments, the coating layer includes amorphous carbon. The inclusion of amorphous carbon in the coating layer can increase the sites for intercalating and deintercalating active ions, improve the specific capacity of the negative electrode material, and can also cooperate with polymers and graphene to improve the stability of the coating layer structure. Amorphous carbon can increase the sites for intercalating and deintercalating active ions and improve the specific capacity of the negative electrode material. The above content of amorphous carbon improves the stability of the coating layer, making the coating layer not easy to fall off and pulverize. - -1 -1 -1 -1 In some optional embodiments, the average particle size Dv50 of the silicon-carbon particles is 5 μm to 20 μm, and can be optionally 5 μm to 10 μm.

[0097] According to the embodiments of the present application, controlling the average particle size Dv50 of the silicon-carbon particles within the above range is beneficial to controlling the overall particle size of the negative electrode material, facilitating the deposition and intercalation / deintercalation of active ions in the negative electrode material, improving the electron transport performance of the negative electrode material, and reducing the side reactions of the electrolyte at the negative electrode.

[0098] Optionally, the average particle size Dv50 of the silicon-carbon particles can be any value among 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm or the range composed of them.

[0099] 1 1 1

[0100] 1 1 1

[0101] 1

[0102] ​

[0103] In some alternative embodiments, the silicon carbide particles include 65% to 78% of silicon element and 22% to 35% of carbon element by mass percentage. Optionally, the silicon carbide particles include 68% to 75% of silicon element and 25% to 32% of carbon element by mass percentage.

[0104] According to the embodiments of the present application, controlling the elements of the silicon carbide particles to have the above mass fractions is beneficial to controlling the overall volume change rate of the silicon carbide particles during the electrochemical cycle of the battery, beneficial to improving the stability of the coating layer and the specific capacity per gram of the negative electrode material.

[0105] In some alternative embodiments, the negative electrode material is granular. In some alternative embodiments, the average particle size Dv 2 50 of the negative electrode material is 5.05 μm to 25 μm, and can be optionally 5.5 μm to 10.5 μm.

[0106] Optionally, the average particle size Dv 2 50 of the negative electrode material can be 5.05 μm, 5.15 μm, 5.20 μm, 5.25 μm, 5.30 μm, 5.35 μm, 5.40 μm, 5.45 μm, 5.50 μm, 5.55 μm, 5.60 μm, 5.65 μm, 5.70 μm,

[0107] 5.75 μm, 5.80 μm, 5.85 μm, 5.90 μm, 5.95 μm, 6.0 μm, 7.0 μm, 8.0 μm, 9.0 μm,

[0108] 10.0 μm, 11.0 μm, 12.0 μm, 13.0 μm, 14.0 μm, 15.0 μm, 16.0 μm, 17.0 μm, 18.0 μm,

[0109] 19.0 μm, 20.0 μm, 21.0 μm, 22.0 μm, 23.0 μm, 24.0 μm, 25.0 μm, or any value within the range composed thereof.

[0110] According to the embodiments of the present application, the negative electrode material having an appropriate volume average particle size Dv 2 50 is beneficial to improving the powder compaction density of the negative electrode material itself, so that the negative electrode has a high specific capacity per gram. Using this negative electrode material can make the compaction density of the electrode sheet relatively high, and can reduce the addition amount of the binder in the negative electrode sheet, thereby improving the energy density of the battery.

[0111] The particle size distribution Dv 1 50 of the silicon carbide particles and the particle size distribution Dv 2 50 of the negative electrode material have the meanings well known in the art. The particle size distribution Dv 1 50, Dv2 50, also known as the average particle size or median particle size, represents the particle size corresponding to 50% of the volume distribution of the negative electrode material. The above-mentioned particle size distributions can be measured by instruments and methods well-known in the art. For example, it can be conveniently measured with a laser particle size analyzer, such as the Mastersizer 3000 type laser particle size analyzer of Malvern Instruments Limited in the UK.

[0112] In some alternative embodiments, the specific surface area of the negative electrode material is 2 m 2 / g to 30 m 2 / g, and can be optionally 3 m 2 / g to 20 m 2 / g.

[0113] Optionally, the specific surface area of the negative electrode material is 2 m 2 / g, 3 m 2 / g, 4 m 2 / g, 5 m 2 / g, 6 m 2 / g, 7 m 2 / g, 8 m 2 / g, 9 m 2 / g, 10 m 2 / g, 11 m 2 / g, 12 m 2 / g, 13 m 2 / g, 14 m 2 / g, 15 m 2 / g, 16 m 2 / g, 17 m 2 / g, 18 m 2 / g, 19 m 2 / g, 20 m 2 / g, 21 m 2 / g, 22 m 2 / g, 23 m 2 / g, 24 m 2 / g, 25 m 2 / g, 26 m 2 / g, 27 m 2 / g, 28 m 2 / g, 29 m 2 / g, 30 m 2 / g, any value within or the range composed of them.

[0114] According to the embodiments of the present application, by controlling the specific surface area of the negative electrode material within the above range, it can provide more active sites for the insertion and extraction of active ions including lithium ions in the negative electrode material, which can improve the specific capacity of the negative electrode material; it is also beneficial to reduce the side reactions of the electrolyte at the negative electrode, and can also reduce the film formation consumption of active ions at the negative electrode, thereby improving the cycle performance of the battery.

[0115] The specific surface area of the negative electrode material has the meaning well-known in the art and can be measured by instruments and methods well-known in the art. For example, it can be measured with reference to the standard for measuring the specific surface area of solid substances by the gas adsorption BET method in GB / T 19587-2004, using the nitrogen adsorption specific surface area analysis and test method for testing and calculating by the BET (Brunauer Emmett Teller) method. Among them, the nitrogen adsorption specific surface area analysis and test can be carried out by a Tri StarⅡ3020 specific surface area and pore size analyzer of Micromeritics Company in the United States.

[0116] In some optional embodiments, the volume change rate of the negative electrode material is 0.5% to 2%.

[0117] Optionally, the volume change rate of the negative electrode material is any value among 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0% or the range composed of them.

[0118] The volume change rate of the negative electrode material can be measured by a dilatometer. The volume change rate of the negative electrode material can be measured by simulating the negative electrode material in the battery during the heating process. As an example, the method for measuring the volume change rate of the negative electrode material includes: weighing M1 g of the negative electrode material, then using a pressure of 300 N to press it into a 3*3*3 cube, placing the prepared cube-shaped negative electrode material on the dilatometer, setting the temperature range from 25°C to 100°C, with a heating rate of 5°C / min, and recording its dimensional change. Then calculate the thermal expansion coefficient of the negative electrode material.

[0119] According to the embodiments of the present application, when the volume change rate of the negative electrode material is within the above range, it is beneficial to improve the certain close contact between the negative electrode material, the conductive agent and the binder, and improve the charge and discharge performance; it is beneficial to reduce the pulverization of the negative electrode material and the repeated generation and rupture of the solid electrolyte interface film (SEI) caused by continuous expansion and contraction, reduce the consumption of the electrolyte inside the battery, and is beneficial to the cycle performance and service life of the battery.

[0120] In some optional embodiments, the D peak intensity I D of the negative electrode material and the G peak intensity I G The ratio I D / I G is 1 to 2.5, and can be optionally 1.2 to 2.

[0121] The D peak and the G peak are characteristic peaks in the Raman spectrum of the negative electrode material. The intensities of the D peak and the G peak can be measured using a laser Raman spectrometer, such as the Advantage 785TM Raman spectrometer. In an exemplary embodiment of the negative electrode material, in the Raman spectrum measured by the Raman spectrometer, the D peak is at 1340 cm -1 ~1360 cm -1 position, the G peak is at 1570 cm -1 ~1590 cm -1 position. Optionally, the D peak is at 1350 cm -1 position, and the G peak is at 1580 cm -1 position. The ratio I D / I G can be used to characterize the ratio of amorphous carbon to graphitic crystalline carbon on the particle surface, and further characterize the degree of surface defects and the coating degree in the coating layer. The peak intensities of the D peak and the G peak are in the above ranges, which is beneficial to reducing the volume expansion of the negative electrode sheet containing the negative electrode material during the battery cycle and improving the cycle performance of the battery.

[0122] When the ratio of the peak intensity I D of the D peak to the peak intensity I G of the G peak is within the above range, it can reduce the irreversible capacity of the negative electrode material during charge and discharge cycling, while ensuring that the coating layer has excellent electrical conductivity, which is beneficial to the performance of the negative electrode material capacity, improve the cycle capacity retention rate of the negative electrode material, and thus improve the first Coulomb efficiency, cycle performance and energy density of the battery monomer using these negative electrode materials.

[0123] The Raman spectrum of the negative electrode material can be measured using instruments and methods well known in the art. For example, a Raman spectrometer is used. As a specific example, a LabRAM HR Evolution type laser micro-Raman spectrometer is used to perform Raman scattering analysis on the negative electrode material. Among them, a solid-state laser with a wavelength of 523 nm is used as the light source, the beam diameter is 1.2 μm, and the power is 1 mW; the measurement mode is macro Raman; a CCD detector is used. The negative electrode material powder is pressed into a tablet, and 3 points are randomly selected on the tablet for testing, and the average value of the three groups of measurement values is obtained. As an example, Figure 2 shows the peak intensity I D of the D peak included in the negative electrode material and the peak intensity I G of the G peak.

[0124] Preparation method of negative electrode material

[0125] In a second aspect, an embodiment of the present application provides a method for preparing a negative electrode material, the method including:

[0126] Providing silicon-carbon particles with a polymer emulsion coated on the surface;

[0127] The silicon-carbon particles coated with a polymer emulsion are treated with a laser to carbonize and graphitize at least part of the polymer in the polymer emulsion to form a coating layer, thereby obtaining the negative electrode material of the first aspect, wherein the coating layer includes graphene and a polymer.

[0128] According to the preparation method of the embodiments of the present application, a carbonized and graphitized coating layer is prepared in-situ, and a certain amount of polymer is contained in the coating layer, which improves the stability and firmness of the coating layer, hinders the pulverization of the negative electrode material due to volume change and complex stress during charge and discharge, improves the close contact between the negative electrode material, the conductive agent and the binder, thereby improving the conductivity of the negative electrode sheet containing the negative electrode material and improving the fast charge and discharge performance of the battery.

[0129] According to the embodiments of the present application, the coating layer of the negative electrode material contains graphene, which improves the conductivity of the coating layer, thereby improving the fast charge and discharge performance of the battery.

[0130] According to the embodiments of the present application, treating the silicon-carbon particles coated with a polymer emulsion with a laser can make the coating layer possibly contain intermediate products in different states during the carbonization of the polymer. On the one hand, this intermediate product can reflect the stability degree of the coating layer, make the coating layer of the negative electrode material have a certain stability, make the negative electrode material and the conductive agent and the binder have a certain close contact, and allow the silicon-carbon particles in the negative electrode material to have a suitable range of volume change.

[0131] In some embodiments, the method for providing silicon-carbon particles coated with a polymer emulsion includes: spraying a polymer emulsion containing a polytetrafluoroethylene emulsion and a chitosan emulsion on the surface of the silicon-carbon particles.

[0132] In some alternative embodiments, the laser type is a carbon dioxide laser;

[0133] In some alternative embodiments, the power during laser treatment is 10W to 150W;

[0134] In some alternative embodiments, the scanning rate of laser treatment is 0.01m / s to 2m / s;

[0135] In some alternative embodiments, the time interval of laser treatment is 0.1S to 1S.

[0136] According to the embodiments of the present application, one or several of the above process conditions can be regulated, so as to control the content of the polymer and graphene in the coating layer of the negative electrode material, and the above negative electrode material can be prepared.

[0137] In the above preparation method, an inert atmosphere can be used for protection when necessary. For example, the inert atmosphere can be selected from one or more of nitrogen, argon, and helium.

[0138] In some alternative embodiments, the polymer emulsion includes a first polymer and a second polymer, and the mass ratio of the first polymer to the second polymer is 1:(0.01 - 2).

[0139] According to the embodiments of the present application, by controlling the mass ratio of the first polymer to the second polymer within the above range, graphene is formed by the first polymer in the polymer emulsion, the second polymer has good heat resistance, excellent chemical corrosion resistance of the material itself, and good creep resistance. They can also be used as binders for active materials. More importantly, the carbonized parts of these polymers provide carbon sites and the remaining second polymer forms a three-dimensional network structure, which can coat the silicon-carbon particles to control the expansion of their size, and at the same time can also play a role in fixing the graphene material formed by the first polymer.

[0140] In some alternative embodiments, the first polymer includes one or more of chitosan, chitin, and cellulose. In some alternative embodiments, the second polymer includes one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyethyleneimine, polyether ether ketone, and ethylene-tetrafluoroethylene copolymer. According to the embodiments of the present application, the coating layer is composed of the above two polymers, which is beneficial to improving the stability of the coating layer and the comprehensive performance of the battery.

[0141] In some alternative embodiments, the average particle size Dv of the silicon-carbon particles 1 is 5 μm to 20 μm, and can be optionally 5 μm to 10 μm.

[0142] In some alternative embodiments, the silicon-carbon particles include 65% to 78% of silicon element and 22% to 35% of carbon element by mass percentage. Optionally, the silicon-carbon particles include 68% to 75% of silicon element and 25% to 32% of carbon element by mass percentage.

[0143] Negative electrode plate

[0144] In a third aspect, the embodiments of the present application provide a negative electrode tab, which includes a negative electrode current collector and a negative electrode active material film layer disposed on at least one side of the negative electrode current collector. The negative electrode active material film layer includes the negative electrode material of the first aspect or the negative electrode material prepared by the preparation method of the second aspect.

[0145] In the battery monomer of the present application, the negative electrode current collector can be made of a material with good electrical conductivity and mechanical strength, and can be optionally a copper foil.

[0146] In the battery cell of the present application, further, the negative electrode active material film layer may alternatively include other negative electrode materials that can be used for the negative electrode of the battery cell. The other negative electrode materials may be selected from one or more of graphite, mesocarbon microbeads (abbreviated as MCMB), hard carbon, and soft carbon, and more preferably graphite. The graphite may be selected from one or more of artificial graphite and natural graphite.

[0147] In the battery cell of the present application, further, the negative electrode active material film layer may alternatively include a conductive agent, a binder, and a thickening agent, and there are no specific restrictions on their types, and those skilled in the art can select according to actual needs.

[0148] Optionally, the conductive agent for the negative electrode active material film layer may be one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; the binder may be one or more of polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS); the thickening agent may be carboxymethyl cellulose (CMC).

[0149] The negative electrode plate can be prepared according to conventional methods in the art. For example, the negative electrode material and optional conductive agent, binder, and thickening agent are dispersed in a solvent, which can be deionized water, to form a uniform negative electrode slurry. The negative electrode slurry is coated on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode plate is obtained.

[0150] Battery cell

[0151] In a fourth aspect, an embodiment of the present application provides a battery cell including the negative electrode plate of the third aspect.

[0152] Specifically, the battery cell includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. The negative electrode plate includes a negative electrode current collector and a negative electrode active material film layer provided on at least one surface of the negative electrode current collector, and the negative electrode active material film layer includes the negative electrode material of the first aspect of the present application.

[0153] In the battery cell of the present application, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector and including a positive electrode active material.

[0154] In the battery cell of the present application, the positive electrode current collector can be made of a material with good electrical conductivity and mechanical strength, and can be selected as aluminum foil.

[0155] In the battery cell of the present application, there is no specific limitation on the specific type of the positive electrode active material. Materials known in the art that can be used for the positive electrode of a battery cell can be adopted, and those skilled in the art can make a selection according to actual needs.

[0156] It should be noted that the battery cell of the present application can be a lithium-ion battery, a sodium-ion battery, and any other battery using the negative electrode material described in the first aspect of the present application.

[0157] When the battery cell of the present application is a lithium-ion battery, optionally, the positive electrode active material can be a metal oxide and its modified material, and can be a lithium transition metal oxide and its modified material. The modified material can be doping modification and / or coating modification of the lithium transition metal oxide. Optionally, the lithium transition metal oxide can be selected from one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium-containing phosphate in olivine structure.

[0158] For example, the positive electrode active material of a lithium-ion battery can be selected from LiCoO 2 、LiNiO 2 、LiMnO 2 、LiMn 2 O 4 、LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LiNi 0.80 Co 0.15 Al 0.05 O 2 、LiFePO 4 (LFP) and LiMnPO 4 among one or more.

[0159] When the battery cell of the present application is a sodium-ion battery, optionally, the positive electrode active material can be selected from transition metal oxides Na x MO 2(M is a transition metal, which can be selected from one or more of Mn, Fe, Ni, Co, V, Cu, Cr, 0 < x ≤ 1), polyanion materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), Prussian blue materials, etc. However, the present application is not limited to these materials, and other materials that can be used as the positive electrode active material of the sodium-ion battery can also be used. These positive electrode active materials can be used alone or in combination of two or more kinds.

[0160] Optionally, the positive electrode active material of the sodium-ion battery can be selected from NaFeO 2 , NaCoO 2 , NaCrO 2 , NaMnO 2 , NaNiO 2 , NaNi 1 / 2 Ti 1 / 2 O 2 , NaNi 1 / 2 Mn 1 / 2 O 2 , Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O 2 , NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 , NaFePO 4 , NaMnPO 4 , NaCoPO 4 , Prussian blue materials, and materials with the general formula A a M b (PO 4 ) c O x Y 3-x (where A is selected from one or more of H + , Li + , Na + , K + and NH 4 + , M is a transition metal cation, which can be selected from one or more of V, Ti, Mn, Fe, Co, Ni, Cu and Zn, Y is a halogen anion, which can be selected from one or more of F, Cl and Br, 0 < a ≤ 4, 0 < b ≤ 2, 1 ≤ c ≤ 3, 0 ≤ x ≤ 2) one or more of them.

[0161] In the battery cell of the present application, further, the positive electrode film layer may further include a binder and / or a conductive agent. There are no specific restrictions on the types of the binder and the conductive agent, and those skilled in the art can select according to actual needs. Optionally, the binder for the positive electrode film layer may include one or more of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE); the conductive agent may include one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0162] The above positive electrode sheet can be prepared according to the conventional methods in the art. For example, the positive electrode active material and optional conductive agent and binder are dispersed in a solvent (such as N-methylpyrrolidone, abbreviated as NMP) to form a uniform positive electrode slurry. The positive electrode slurry is coated on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode sheet is obtained.

[0163] In the battery cell of the present application, there are no specific restrictions on the type of the electrolyte, and it can be selected according to needs. The electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolyte solution). When the electrolyte is an electrolyte solution, the electrolyte solution includes an electrolyte salt and a solvent. It is characterized in that the specific types of the electrolyte salt and the solvent are not specifically restricted and can be selected according to actual needs.

[0164] When the battery cell of the present application is a lithium-ion battery, optionally, the electrolyte salt can be selected from LiPF 6 (lithium hexafluorophosphate), LiBF 4 (lithium tetrafluoroborate), LiClO 4 (lithium perchlorate), LiAsF 6 (lithium hexafluoroarsenate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium bis(oxalate) borate), LiPO 2 F 2 (lithium difluorophosphate), LiDFOP (lithium difluorodioxalate phosphate), and LiTFOP (lithium tetrafluorooxalate phosphate) and one or more of them.

[0165] When the battery cell of the present application is a sodium-ion battery, optionally, the electrolyte salt can be selected from NaPF 6 , NaClO 4 , NaBCl 4 , NaSO 3 CF 3 and Na(CH 3 )C 6 H 4 SO 3 and one or more of them.

[0166] In the battery cell of the present application, optionally, the solvent may be one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0167] The electrolyte may also optionally include additives, and there is no specific limitation on the types of additives, which can be selected according to requirements. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain performance of the battery, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature performance of the battery, additives for improving the low-temperature performance of the battery, etc.

[0168] In the battery cell of the present application, the separator is disposed between the positive electrode plate and the negative electrode plate to play a role of isolation. There is no particular limitation on the type of the separator, and any well-known porous structure separator with good chemical stability and mechanical stability can be selected, such as one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer can be the same or different.

[0169] [Preparation method of battery cell]

[0170] The preparation method of the battery cell may include the step of assembling the negative electrode plate, the positive electrode plate, and the electrolyte to form a battery cell.

[0171] In some alternative embodiments, the positive electrode plate, the separator, and the negative electrode plate may be wound or laminated in sequence, so that the separator is between the positive electrode plate and the negative electrode plate to play a role of isolation, obtaining an electrode assembly (i.e., an electrode core); the electrode assembly is placed in an outer package, injected with electrolyte and sealed to obtain a battery cell. In some alternative embodiments, through processes such as vacuum packaging, standing, formation, and shaping, a battery cell is obtained.

[0172] The battery cell can be prepared by methods well-known in the art. As an example, the positive electrode sheet, the separator, and the negative electrode sheet are wound (or laminated) in sequence, with the separator positioned between the positive electrode sheet and the negative electrode sheet to play a role in isolation, obtaining an electrode core. The electrode core is placed in an outer package, electrolyte is injected and sealed to obtain the battery cell.

[0173] In some alternative embodiments, the preparation of the battery cell may further include the step of preparing the positive electrode sheet. As an example, the positive active material, the conductive agent, and the binder can be dispersed in a solvent (such as N-methylpyrrolidone, abbreviated as NMP) to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode sheet is obtained.

[0174] In some alternative embodiments, the preparation of the battery cell may further include the step of preparing the negative electrode sheet. As an example, the negative active material, the binder, and optionally the thickening agent and the conductive agent are dispersed in a solvent, which can be deionized water, to form a uniform negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode sheet is obtained.

[0175] The positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly by a lamination process or a winding process, with the separator positioned between the positive electrode sheet and the negative electrode sheet to play a role in isolation; the electrode assembly is placed in an outer package, electrolyte is injected and sealed, and then the battery can be obtained. The separator in the electrode assembly includes at least one or several separators as described in the present application.

[0176] The outer package of the battery is used to encapsulate the electrode assembly and the electrolyte. In some embodiments, the outer package of the battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, such as including one or several of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0177] The present application does not particularly limit the shape of the battery, which can be cylindrical, square, or any other arbitrary shape. As Figure 1 is a battery cell 5 with a square structure as an example.

[0178] In some embodiments, referring to Figure 2 , the outer package may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte infiltrates in the electrode assembly 52. The number of the electrode assemblies 52 included in the battery cell 5 can be one or several, which can be adjusted according to requirements.

[0179] Battery

[0180] In a fifth aspect, an embodiment of the present application provides a battery, including the battery cell of the fourth aspect.

[0181] In some optional embodiments, the battery cells can be assembled into a battery module or a battery. The number of battery cells included in the battery module or the battery can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0182] Figure 3 This is the battery module 4 as an example. Refer to Figure 3 , in the battery module 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other manner. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0183] Optionally, the battery module 4 can further include a housing having an accommodation space, and a plurality of battery cells 5 are accommodated in the accommodation space.

[0184] In some optional embodiments, the above battery module can be further assembled into a battery, and the number of battery modules included in the battery can be adjusted according to the application and capacity of the battery.

[0185] Figure 4 This is the battery 1 as an example. Refer to Figure 4 and Figure 5 , in the battery 1, it can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0186] In some embodiments of the present application, the battery cells according to the present application can be assembled into a battery module, and the number of battery cells included in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0187] In some optional embodiments, the above battery module can be further assembled into a battery, and the number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0188] Electrical device

[0189] In a sixth aspect, an embodiment of the present application provides an electrical device, including the battery of the fifth aspect.

[0190] The electrical device of the present application includes the battery cell of the first aspect of the present application, and thus has at least the advantages of the application of the battery cell.

[0191] The battery cell or battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0192] Figure 6 It is a schematic diagram of an electrical device as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the demand of the electrical device for high energy density, a battery pack or a battery module can be adopted.

[0193] Another example of an electrical device can be a mobile phone, a tablet computer, a laptop computer, etc. This electrical device usually requires being thin and light, and a battery cell can be used as the power source.

[0194] Example

[0195] The following embodiments more specifically describe the content disclosed in the present application. These embodiments are only for illustrative purposes, because various modifications and changes within the scope of the content disclosed in the present application are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the embodiments are all commercially available.

[0196] Example 1

[0197] Preparation of the negative electrode material: A mixed solution obtained by mixing 10 g of a polytetrafluoroethylene emulsion with a solid content of 10% and 20 g of a chitosan emulsion with a solid content of 20% is sprayed on the surface of 100 g of silicon-carbon particles for coating. The silicon-carbon particles include 70% silicon element and 30% carbon element by mass percentage, and the average particle size Dv50 of the silicon-carbon particles is 5 microns. Then it is dried at 100 °C for 3 h to obtain the silicon-carbon material pretreated with polytetrafluoroethylene and chitosan.

[0198] The pretreated silicon-carbon material is processed by carbon dioxide laser-induced technology. Laser processing is carried out with a laser power range of 50 W, a scanning rate of 0.2 m / s, a time interval of 0.1 s, and a processing time of 10 s to obtain the negative electrode material.

[0199] Preparation of Lithium Battery:

[0200] (1) Preparation of Negative Electrode Plate:

[0201] Mix the prepared negative electrode material with conductive agent Super P, thickening agent CMC, and binder styrene-butadiene rubber (SBR) uniformly in deionized water to form a negative electrode slurry. The solid content in the negative electrode slurry is 30 wt%, and the mass ratio of the prepared negative electrode material, Super P, CMC, and binder styrene-butadiene rubber (SBR) in the solid components is 97.5:1.5:0.5:0.5. Coating the negative electrode slurry on the current collector copper foil and drying it at 85°C, then performing cold pressing, edge trimming, slicing, and slitting, and drying it in a vacuum at 120°C for 12 h to make the negative electrode plate.

[0202] (2) Preparation of Electrolyte:

[0203] In a glove box filled with argon (water content < 10 ppm, oxygen content < 1 ppm), add ethylene carbonate and ethyl methyl carbonate to a beaker in a mass ratio of 1:1 and stir to mix. Subsequently, slowly add LiPF6 and LiFSI so that their mass fractions in the electrolyte are 4% respectively. After the lithium salts are completely dissolved, add vinylene sulfate (DTD) and 1,3-propane sultone to the above electrolyte and mix evenly. The mass fractions of vinylene sulfate (DTD) and 1,3-propane sultone are 0.5% to obtain the electrolyte.

[0204] (3) Preparation of Positive Electrode Plate: Make a positive electrode slurry by mixing the positive electrode active material, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP). The solid content in the positive electrode slurry is 50 wt%, and the mass ratio of LiNi 0.5 Co 0.2 Mn 0.3 O 2 , Super P, and PVDF is 8:1:1. Coating the positive electrode slurry on the current collector aluminum foil and drying it at 85°C, then performing cold pressing, and then performing edge trimming, slicing, and slitting, and drying it in a vacuum at 85°C for 4 h to make the positive electrode plate.

[0205] (4) Separator: Select a PE material with a thickness of 9 μm as the separator.

[0206] Stack the prepared positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator placed in the middle of the positive and negative electrode sheets to isolate the positive and negative electrodes, wind to obtain a bare battery cell, weld the electrode tabs, place the bare battery cell in the outer packaging, inject the above-prepared electrolyte into the dried battery cell, and perform encapsulation, standing, formation, shaping, capacity testing, etc. to complete the preparation of the lithium-ion battery (the thickness of the soft-pack lithium-ion battery is 4.0 mm, the width is 60 mm, and the length is 140 mm).

[0207] Examples 2-1 to 2-5

[0208] Different from Example 1, the relevant parameters of the laser treatment in the preparation process of the negative electrode material are adjusted to obtain different negative electrode materials.

[0209] Examples 3-1 to 3-8

[0210] Different from Example 1, the relevant parameters of the polymer emulsion in the preparation process of the negative electrode material are adjusted to obtain different negative electrode materials.

[0211] Comparative example 1

[0212] The silicon-carbon particles in Example 1 are used, and their average particle size Dv50 is 5 microns.

[0213] Test part

[0214] (1) Cycle performance test of the lithium-ion battery.

[0215] Adjust the ambient temperature to 25°C, perform the first charge and discharge. Charge the battery cell at a charging current of 1C to 4.2V, perform constant-voltage charging to 0.05C, stand for 10 min, and perform constant-current discharge at 1C until the discharge cut-off voltage of 3.0V. This is one charge-discharge cycle. Record the discharge capacity as C0. Perform 500 cycles according to the above charge-discharge process. The discharge capacity at the 500th cycle is C1. The cycle capacity retention rate of the battery cell = C1 / C0 * 100%.

[0216] (2) Charge-discharge efficiency (rate performance) test of the lithium-ion battery

[0217] Use a blue battery tester to test the performance of the lithium-ion battery. The test conditions are as follows: Under the environment of 25°C, the test method for the discharge capacity retention rate at a discharge rate of 2C is as follows:

[0218] The secondary battery is charged at a constant current with a charging rate of 0.5C until the voltage of the secondary battery reaches 4.2V; the secondary battery is charged at a constant voltage with a charging voltage of 4.2V until the charging rate reaches 0.025C; the secondary battery is discharged at a constant current with a discharging rate of 0.5C until the voltage of the secondary battery reaches 3.0V; the above process is repeated 3 times, and the average discharging capacity of the secondary battery is taken as the actual discharging capacity of the secondary battery (the discharging capacity at a discharging rate of 0.5C).

[0219] The secondary battery is charged at a constant current with a charging rate of 0.5C until the voltage of the secondary battery reaches 4.2V; the secondary battery is charged at a constant voltage with a charging voltage of 4.2V until the charging rate reaches 0.025C; the secondary battery is discharged at a constant current with a discharging rate of 2C until the voltage of the secondary battery reaches 3.0V; the above process is repeated 3 times, and the average discharging capacity is taken as the actual discharging capacity of the secondary battery at a discharging rate of 2C.

[0220] The retention rate of the discharging capacity at a discharging rate of 2C = the actual discharging capacity at a discharging rate of 2C / the actual discharging capacity of the secondary battery at 0.5C.

[0221] (3) Test method for the K value: The K value of the battery refers to the voltage drop of the battery per unit time, usually with the unit of mV / d, which is an index used to measure the self-discharge rate of lithium batteries. The method for measuring the K value is as follows: measure OCV1 at time t1; measure OCV2 at time t2; K = (OCV1 - OCV2) / (t1 - t2), where t1 - t2 = 14 days.

[0222]

[0223]

[0224] In the battery industry, the K value refers to the voltage drop of the battery per unit time, usually with the unit of mV / h, which is an index used to measure the self-discharge rate of lithium batteries and can evaluate the stability and reliability of the battery. The K value is an important parameter for judging the quality of lithium batteries. By measuring the K value, the self-discharge rate of the battery cell is ensured to be within the set standard range, so as to ensure that the battery can work normally and reliably.

[0225] As can be seen from the data in Table 1, the negative electrode material of the present application includes silicon-carbon particles and a coating layer coated on the silicon-carbon particles, and the coating layer contains graphene, which significantly improves the cycle life and charge-discharge efficiency of the negative electrode material, thereby enabling a substantial improvement in the performance of the battery cell. After testing, during the process of heating the negative electrode material of the embodiment of the present application from 25°C to 800°C in an inert non-oxidizing gas atmosphere, the weight loss rate of the coating layer can be between 0.1% and 3.5%. In Comparative Example 1, there is no coating layer, and the cycle performance and charge-discharge performance of the embodiment battery are relatively high. The reason for the analysis may be that: compared with the embodiment, the comparative example has no coating layer, and its volume change rate may be larger; and the negative electrode material has a certain amount of polymer, which can allow a large volume change of the silicon-carbon particles, improving the stability of the negative electrode material. The negative electrode material of the embodiment has a certain amount of graphene, reducing the internal resistance of the negative electrode plate.

[0226] The above is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present application can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should be covered within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A negative electrode material, characterized in that, it comprises: silicon-carbon particles, and a coating layer, comprising graphene and a polymer, wherein the coating layer at least partially coats the surface of the silicon-carbon particles.

2. The negative electrode material according to claim 1, characterized in that, based on the total mass of the negative electrode material, the negative electrode material comprises 0.1% to 5% of the coating layer.

3. The negative electrode material according to claim 1 or 2, characterized in that, when the coating layer is heated from 25°C to 800°C in an inert non-oxidizing gas atmosphere, the weight loss rate of the coating layer is 0.1% to 3.5%, optionally 0.5% to 2%.

4. The negative electrode material according to any one of claims 1 to 3, characterized in that, the average number of layers Dn80 of the graphene is ≤ 3, optionally 1 to 2.

5. The negative electrode material according to any one of claims 1 to 4, characterized in that, the coating layer satisfies at least one of the following conditions: 1) The coating layer contains an intermediate product; optionally, the intermediate product contains one or more of fluorine element, nitrogen element, and oxygen element; 2) The coating layer comprises amorphous carbon.

6. The negative electrode material according to any one of claims 1 to 5, characterized in that, the polymer comprises one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyethyleneimine, polyetheretherketone, and ethylene-tetrafluoroethylene copolymer.

7. The negative electrode material according to any one of claims 1 to 6, characterized in that, the negative electrode material satisfies any one of the following conditions: 1) The negative electrode material is granular, and the average particle size Dv of the negative electrode material 2 50 is 5.05 μm to 25 μm, and can be optionally 5.5 μm to 10.5 μm; 2) The specific surface area of the negative electrode material is 2 m 2 / g to 30 m 2 / g, and can be optionally 3 m 2 / g to 20 m 2 / g; 3) The intensity ID of the D peak in the Raman spectrum of the negative electrode material D and the intensity IG of the G peak G The ratio I D / I G is 1 to 2.5, and can be optionally 1.2 to 2. Among them, the D peak is located at 1340 cm -1 to 1360 cm -1 The position of the G peak is located at 1570 cm -1 to 1590 cm -1 position.

8. A method for preparing a negative electrode material, characterized in that, the method comprises: providing silicon-carbon particles coated with a polymer emulsion; treating the silicon-carbon particles coated with the polymer emulsion with a laser to carbonize and graphitize at least part of the polymer in the polymer emulsion to form a coating layer, thereby obtaining the negative electrode material.

9. The preparation method according to claim 8, characterized in that, the method satisfies at least one of the following conditions: 1) The type of the laser is a carbon dioxide laser; 2) The power during the laser treatment is 10 W to 150 W; 3) The scanning rate of the laser treatment is 0.01 m / s to 2 m / s; 4) The time interval of the laser treatment is 0.1 s to 1 s.

10. The preparation method according to claim 8 or 9, characterized in that, the silicon-carbon particles satisfy at least one of the following conditions: 1) The average particle size Dv of the silicon carbide particles 1 is 5 μm to 20 μm, and can be optionally 5 μm to 10 μm; 2) The silicon-carbon particles comprise 65% to 78% of silicon element and 22% to 35% of carbon element by mass percentage.

11. The preparation method according to any one of claims 8 to 10, characterized in that, the polymer emulsion comprises a first polymer and a second polymer, and the mass ratio of the first polymer to the second polymer is 1:(0.01 to 2).

12. The preparation method according to claim 11, characterized in that, the first polymer comprises one or more of chitosan, chitin, and cellulose; and / or, the second polymer comprises one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyethyleneimine, polyetheretherketone, and ethylene-tetrafluoroethylene copolymer.

13. A negative electrode sheet, It is characterized in that it includes a negative current collector and a negative active material film layer disposed on at least one side of the negative current collector, and the negative active material film layer includes the negative electrode material according to any one of claims 1 to 7 or the negative electrode material prepared by the preparation method according to any one of claims 8 to 12.

14. A battery cell It is characterized in that it includes the negative electrode plate according to claim 13.

15. A battery It is characterized in that it includes the battery cell according to claim 14.

16. An electrical device It is characterized in that it includes the battery according to claim 15.

Images