Negative electrode material, negative electrode sheet, electrochemical device, and electronic device

Abstract

The present disclosure provides a negative electrode material, a negative electrode sheet, an electrochemical device, and an electronic device. The negative electrode material includes a silicon-based material, wherein, for a test battery in which an electrode containing the negative electrode material is combined with a counter electrode composed of metallic lithium, a first efficiency of the test battery is 81% to 86%, and wherein, when a potential of the electrode in the test battery becomes 0.17 V, a discharge capacity is within a range of 35% to 65% of a first discharge capacity of the test battery. The present disclosure limits a lithium intercalation plateau of silicon-based material particles such that, when a potential of a silicon-based negative electrode material becomes 0.17 V in a test half-cell, a lithium intercalation capacity is within a range of 35% to 65% of a first lithium intercalation capacity of the test half-cell, thereby ensuring amorphous characteristics of the silicon-based material, significantly improving cycle performance of the negative electrode material, and reducing an expansion rate of an electrode assembly during cycling.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of electronic technology, and in particular, to a negative electrode material, a negative electrode sheet, an electrochemical device, and an electronic device. BACKGROUND

[0002] Silicon-based materials have a theoretical specific capacity of up to 4200 mAh / g, and are a promising negative electrode material for the next generation of electrochemical devices (e.g., lithium ion batteries). For example, silicon-oxygen materials have a high specific capacity of 2400 mAh / g, however, silicon-oxygen materials have a large volume expansion of 150% during lithium extraction, which causes the connection between active materials to fail, and causes the electrode assembly to expand while affecting its cycle performance.

[0003] Currently, silicon-based materials can be made to have a high reversible capacity by limiting the charge-discharge characteristics of the silicon-based materials. However, the current improvement scheme is not satisfactory. SUMMARY

[0004] In view of the above-mentioned disadvantages of the prior art, the present disclosure can ensure the amorphous characteristics of silicon-based materials by limiting the lithium intercalation plateau of silicon-based material particles, thereby significantly improving the cycle performance of the negative electrode material and reducing the expansion rate of the electrode assembly during cycling.

[0005] The present disclosure provides a negative electrode material, comprising: a silicon-based material, wherein, for a test battery in which an electrode containing the negative electrode material is combined with a counter electrode composed of metallic lithium, the first efficiency of the test battery is 81% to 86%, and wherein the discharge capacity of the electrode in the test battery when the potential of the electrode becomes 0.17 V is in the range of 35% to 65% of the first discharge capacity of the test battery.

[0006] In the above negative electrode material, wherein the charge capacity of the electrode in the test battery when the potential of the electrode becomes 0.4 V is in the range of 35% to 65% of the first charge capacity of the test battery.

[0007] In the above negative electrode material, wherein the first discharge capacity of the test battery is in the range of 2000 mAh / g to 2400 mAh / g.

[0008] In the above negative electrode material, wherein the silicon-based material comprises M y SiO x , 0≤y≤4, 0≤x≤4, and M comprises at least one of Li, Mg, Ti, or Al.

[0009] In the negative electrode material described above, wherein the particle of the silicon-based material has a first peak intensity I1 in a diffraction pattern tested by X-ray diffraction test attributed to a range of 20.5°-21.5°, and a second peak intensity I2 attributed to a range of 28.0°-29.0°, wherein 0

[0010] In the negative electrode material described above, wherein the silicon-based material has an average particle size of 0.5 μm-20 μm.

[0011] In the negative electrode material described above, wherein the silicon-based material has a specific surface area of 1 m 2 / g-30 m 2 / g.

[0012] The present disclosure also provides a negative electrode tab, comprising: a current collector; an active material layer on the current collector; wherein the active material layer comprises any of the negative electrode materials described above.

[0013] The present disclosure also provides an electrochemical device, comprising: a positive electrode tab; a negative electrode tab; a separator film disposed between the positive electrode tab and the negative electrode tab; wherein the negative electrode tab is the negative electrode tab described above.

[0014] The present disclosure also provides an electronic device comprising the electrochemical device described above.

[0015] The present disclosure limits the lithium intercalation platform of the silicon-based material particles, so that the lithium intercalation capacity of the silicon-based negative electrode material is in the range of 35%-65% of the first lithium intercalation capacity of the test half-cell when the potential of the test half-cell is 0.17 V, thereby ensuring the amorphous characteristics of the silicon-based material, significantly improving the cycle performance of the negative electrode material, and reducing the expansion rate of the electrode assembly during the cycle process. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a schematic diagram of the negative electrode tab of the present disclosure.

[0017] Figure 2 is a schematic diagram of the electrode assembly of the electrochemical device of the present disclosure.

[0018] Figure 3 shows the charge-discharge curve of the silicon-based material in Example 13 of the present disclosure in a test battery.

[0019] Figure 4 shows the X-ray diffraction pattern of the silicon-based material particles in Example 20 of the present disclosure. DETAILED DESCRIPTION

[0020] The following examples can enable those skilled in the art to more fully understand the present disclosure, but in no way limit the present disclosure.

[0021] Silicon-based materials can significantly improve the energy density of electrode assemblies as next-generation high-capacity negative electrode materials, but have poor electrical conductivity and undergo large volume expansion and contraction during lithium intercalation and deintercalation.

[0022] The present disclosure can maintain the amorphous characteristics of silicon-based materials by limiting the lithium intercalation plateau of silicon-based material particles. The presence of silicon grains in silicon-based materials can limit the cycle performance of electrode assemblies and corresponding electrochemical devices, so the size of silicon in silicon-based materials should be reduced as much as possible. When silicon-based materials (e.g., silicon-oxygen materials) maintain amorphous characteristics, the cycle performance of negative electrode materials can be effectively improved due to the avoidance of the effects of silicon grains.

[0023] Some embodiments of the present disclosure provide a negative electrode material including a silicon-based material. In some embodiments, the silicon-based material includes M y SiO x , 0≤y≤4, 0≤x≤4, and M includes at least one of Li, Mg, Ti, or Al. In some embodiments, a test battery including an electrode containing the negative electrode material and a counter electrode composed of metallic lithium has a first efficiency of 81% to 86%, and wherein the discharge capacity of the electrode in the test battery when the potential of the electrode becomes 0.17 V is in the range of 35% to 65% of the first discharge capacity of the test battery. In some embodiments, the negative electrode material containing the silicon-based material particles described above can be produced by adjusting the lithium doping modification conditions of the silicon compound. For example, when lithium doping is performed using a heating method commonly used in the art, the amount and type of lithium compound generated can be controlled by changing the calcination conditions. In addition, as a method of adjusting the relationship between the charge capacity of the test battery and the potential of the electrode to satisfy the above range, there is a method of performing rinsing with a solvent such as water and ethanol, etc. after lithium doping modification.

[0024] The higher the proportion of the discharge capacity of the silicon-based material negative electrode in the test battery when the potential of the electrode becomes 0.17 V to the first discharge capacity of the test battery, the better the room temperature and high temperature cycle performance of the silicon-based material in a full battery, and the lower the expansion rate of the electrode assembly. This is because the higher the aforementioned capacity ratio, the closer the active material is to the characteristics of an amorphous silicon-based material, i.e., the smaller the disproportionation degree of the silicon compound, and the smaller the expansion and contraction of the silicon compound caused by battery charging and discharging can be suppressed, thereby effectively improving the cycle performance and expansion rate of the corresponding electrochemical device. In addition, due to the limitations of the characteristics of the silicon-based material, this capacity ratio has an upper limit of 65%.

[0025] In some embodiments, the charge capacity of the electrode in the test battery when the potential of the electrode in the test battery becomes 0.4 V is in the range of 35% to 65% of the first charge capacity of the test battery. In some embodiments, to meet the above range of the charge capacity, the lithium doping modification conditions of the silicon compound can be adjusted. The lower the ratio of the charge capacity of the silicon-based negative electrode in the test battery when the potential of the electrode in the test battery becomes 0.4 V to the first charge capacity of the test battery, the better the cycle performance of the silicon-based material in the full battery at room temperature and high temperature, and the lower the expansion rate of the electrode assembly. This is because the lower the ratio, the closer the active material is to the characteristics of amorphous silicon-based materials, i.e., the smaller the disproportionation degree of the silicon compound, and the smaller the expansion and contraction of the silicon compound caused by battery charging and discharging can be inhibited, thereby effectively improving the cycle performance and expansion rate of the corresponding electrochemical device. In addition, due to the limitations of the characteristics of the silicon-based material, there is a lower limit of 35% for this capacity ratio.

[0026] In some embodiments, the first discharge capacity of the test battery is in the range of 2000 mAh / g to 2400 mAh / g. In some embodiments, to meet the above range of the charge capacity, any suitable method such as adjusting the lithium doping modification conditions of the silicon compound can be used. The higher the first discharge capacity of the test battery, the less the surface lithium doping amount, so the lower the first efficiency and the higher the expansion rate; the lower the first discharge capacity of the test battery, the more the surface lithium doping amount, so the higher the first efficiency and the lower the expansion rate. When the first discharge capacity of the test battery is too low, it means that the lithium doping amount is too much, which will cause the gelation of the slurry, thereby reducing the cycle performance of the negative electrode material; and when the first discharge capacity of the test battery is too high, the lithium doping amount is too low and the first efficiency is too low, which will cause poor cycle performance. Therefore, the first discharge capacity of the test battery is set in the range of 2000 mAh / g to 2400 mAh / g.

[0027] In some embodiments, the silicon-based material is doped with at least one of Li, Mg, Ti, or Al elements, which helps to improve the cycle performance and expansion rate of the prepared electrochemical device.

[0028] In some embodiments, the intensity of the first peak in the diffraction pattern of the particles of the silicon-based material tested by X-ray diffraction is I1, and the intensity of the second peak is I2, where 0 < I2 / I1≤ 3. As the value of I2 / I1 increases, the cycle performance of the electrochemical device decreases and the expansion rate increases. The value of I2 / I1 reflects the degree of influence of the silicon-based material on disproportionation, and the larger the value, the larger the size of the nanosilicon grains generated by the internal SiO disproportionation, which will cause the stress in the local area to increase sharply during the lithium intercalation process, thereby causing structural damage during the cycle of the material, thereby reducing the cycle performance and increasing the expansion rate of the corresponding electrochemical device.

[0029] In some embodiments, the average particle diameter of the silicon-based material is 0.5 μm to 20 μm. In some embodiments, the specific surface area of the silicon-based material is 1 m 2 / g to 30 m 2 / g. If the average particle diameter of the silicon-based material is too small, the silicon-based material is easily agglomerated, and consumes more electrolyte to form a solid electrolyte interface (SEI) film due to a large specific surface area. If the average particle diameter of the silicon-based material is too large, it is not good for suppressing the volume expansion of the silicon-based material, and easily causes deterioration of the conductivity of the active material layer containing the silicon-based material. In addition, as the average particle diameter of the silicon-based material particles increases, the specific surface area decreases, and the cycle performance and the expansion rate of the electrochemical device first improve and then deteriorate. This is because when the average particle diameter is large, the stress of the silicon-based material particles is large and easily broken, and continuously generates fresh surfaces to consume electrolyte, which can make the cycle performance and the expansion rate of the electrochemical device poor; and when the average particle diameter of the silicon-based material is small, the large specific surface area can increase side reactions, thereby deteriorating the cycle performance and the expansion rate of the electrochemical device.

[0030] In some embodiments, the surface of the silicon-based material particles can contain a carbon coating, a polymer coating, or a composite thereof. In some embodiments, the carbon coating contains at least one of amorphous carbon, carbon nanotubes, carbon nanoparticles, vapor-deposited carbon fibers, or graphene. In some embodiments, the polymer coating contains at least one of polyvinylidene fluoride or a derivative thereof, carboxymethyl cellulose or a derivative thereof, sodium carboxymethyl cellulose or a derivative thereof, polyvinylpyrrolidone or a derivative thereof, polyacrylic acid or a derivative thereof, or polybutadiene rubber. When the surface of the silicon-based material has a carbon coating, the conductivity of the silicon-based material can be improved, and thus the battery characteristics can be improved. As a method of forming the carbon coating, a method of coating the silicon-based material with a carbon material can be used. In some embodiments, the mass percentage of the carbon coating with respect to the total mass of the silicon-based material and the carbon coating is 5% to 20%. If the mass percentage of the carbon coating is in the above range, on the one hand, the conductivity can be improved, and on the other hand, a silicon-based material with a high capacity can be contained at an appropriate ratio, and sufficient battery capacity and volumetric energy density can be ensured.

[0031] In some embodiments, the negative electrode material further includes carbon materials, a conductive agent, and a binder. In some embodiments, the carbon materials in the negative electrode material include graphite and / or graphene, etc. In some embodiments, the conductive agent may include at least one of conductive carbon black, sheet graphite, graphene, or carbon nanotubes. In some embodiments, the binder may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamide-imide, polysiloxane, polystyrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene.

[0032] like Figure 1 As shown, some embodiments of this disclosure provide a negative electrode sheet, which includes a current collector 1 and an active material layer 2. The active material layer 2 is located on the current collector 1. It should be understood that, although Figure 1 The active material layer 2 is shown as being located on one side of the current collector 1, but this is merely exemplary, and the active material layer 2 may be located on both sides of the current collector 1. In some embodiments, the current collector of the negative electrode sheet may include at least one of copper foil, aluminum foil, nickel foil, or carbon-based current collector. In some embodiments, the active material layer 2 may include any of the aforementioned negative electrode materials.

[0033] In some embodiments, the active material layer comprises a silicon-based material, a carbon material, a conductive agent, and a binder, wherein the mass ratio of the silicon-based material, carbon material, conductive agent, and binder is 5–96:5–90:0.5–10:0.5–10. In some embodiments, the silicon-based material comprises M y SiO x The form 0 ≤ y ≤ 4, 0 ≤ x ≤ 4, and M includes at least one of Li, Mg, Ti, or Al. In some embodiments, the carbon material includes graphite and / or graphene, etc. In some embodiments, the conductive agent may include at least one of conductive carbon black, sheet graphite, graphene, or carbon nanotubes. In some embodiments, the binder may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamide-imide, polysiloxane, polystyrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene.

[0034] like Figure 2As shown, some embodiments of the present disclosure provide an electrochemical device, an electrode assembly of the electrochemical device includes a positive electrode tab 10, a negative electrode tab 12, and a separator 11 disposed between the positive electrode tab 10 and the negative electrode tab 12. The positive electrode tab 10 can include a positive electrode current collector and a positive electrode active material layer coated on the positive electrode current collector. In some embodiments, the positive electrode active material layer can be coated only on a partial area of the positive electrode current collector. The positive electrode active material layer can include a positive electrode active material, a conductive agent, and a binder. The positive electrode current collector can employ an Al foil, and also other positive electrode current collectors commonly used in the art. The conductive agent of the positive electrode tab can include at least one of conductive carbon black, flake graphite, graphene, or carbon nanotube. The binder in the positive electrode tab can include at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, a styrene-acrylate copolymer, a styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The positive electrode active material includes, but is not limited to, at least one of lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel-manganese, lithium nickel-cobaltate, lithium iron phosphate, lithium nickel-cobalt-aluminate, or lithium nickel-cobalt-manganate, which can be doped or coated.

[0035] In some embodiments, the separator 11 includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one of high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. In particular, polyethylene and polypropylene have a good effect on preventing short circuits, and can improve the stability of the battery through the shutdown effect. In some embodiments, the thickness of the separator is in the range of about 5 μm to 500 μm.

[0036] In some embodiments, the surface of the separator film can further include a porous layer disposed on at least one surface of the separator film, the porous layer including inorganic particles and a binder, the inorganic particles including at least one of aluminum oxide (AI2O3), silicon oxide (SiO2), magnesium oxide (MgO), titanium oxide (TiO2), hafnium dioxide (HfO2), tin oxide (SnO2), cerium dioxide (CeO2), nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. In some embodiments, the pores of the separator film have a diameter in a range of about 0.01 pm to 1 pm. The binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, carboxymethyl cellulose na, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The porous layer of the surface of the separator film can improve the heat resistance, oxidation resistance, and electrolyte infiltration properties of the separator film, and enhance the adhesion between the separator film and the electrode sheet.

[0037] In some embodiments, the negative electrode sheet 12 can be as described above.

[0038] In some embodiments of the present disclosure, the electrode assembly of the electrochemical device is a jelly-roll electrode assembly or a stacked electrode assembly.

[0039] In some embodiments, the electrochemical device includes a lithium ion battery, but the present disclosure is not limited thereto. In some embodiments, the electrochemical device can further include an electrolyte. In some embodiments, the electrolyte includes, but is not limited to, at least two of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethylene carbonate (EC), propylene carbonate (PC), propyl propionate (PP). In addition, the electrolyte can further include at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), or dinitrile compound as an electrolyte additive. In some embodiments, the electrolyte further includes a lithium salt.

[0040] In some embodiments of the present disclosure, taking a lithium ion battery as an example, the positive electrode sheet, the separator film, and the negative electrode sheet are sequentially wound or stacked into an electrode piece, and then packaged in, for example, an aluminum plastic film, injected with an electrolyte, and formed into a lithium ion battery through formation and packaging. Then, the prepared lithium ion battery is subjected to performance testing and cycle testing.

[0041] Those skilled in the art will understand that the preparation method of the electrochemical device (e.g., lithium ion battery) described above is only an embodiment. Other methods commonly used in the art can be employed without departing from the content of the present disclosure.

[0042] The electronic device of the present disclosure is not particularly limited, and can be any electronic device known in the prior art. In some embodiments, the electronic device can include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile, a portable copier, a portable printer, a head-mounted stereo headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio recorder, a radio, a backup power supply, an electric motor, an electric vehicle, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a home-use large storage battery, and a lithium-ion capacitor, etc.

[0043] Some specific examples and comparative examples are listed below to better illustrate the present disclosure, with lithium-ion batteries as examples.

[0044] Example 1

[0045] Preparation of the negative active material: the lithium intercalation silicon-oxygen material with different degrees of disproportionation prepared at different temperatures was selected, so that the discharge capacity of the test half-cell was 2323 mAh / g, the first efficiency was 83.3%, the discharge 0.17V capacity ratio was 25%, the charge 0.4V capacity ratio was 50.5%, and the I2 / I1 value was 0.41.

[0046] Preparation of the negative electrode sheet: the thickness of the copper foil used as the current collector was 10 μm; the binder used was polyacrylic acid; the negative active material, conductive carbon black, and binder were mixed in a mass ratio of 95:1.2:3.8 and then dispersed in water to form a slurry, which was then stirred, coated on the current collector, dried, cold-pressed, and slitted to obtain the negative electrode sheet.

[0047] Preparation of the positive electrode sheet: the positive active material LiCoO2, conductive carbon black, and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 96.7:1.7:1.6 in an N-methyl pyrrolidone solvent system, and then uniformly stirred and mixed, coated on an aluminum foil, and then dried and cold-pressed to obtain the positive electrode sheet.

[0048] Preparation of the battery: a polyethylene porous polymer film was used as a separator, and the positive electrode sheet, the separator, and the negative electrode sheet were sequentially stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to play a separating role, and then wound to obtain an electrode assembly. The electrode assembly was placed in an outer packaging aluminum plastic film, injected with an electrolyte containing ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1, and packaged, and then subjected to processes such as formation, degassing, and edge cutting to obtain a lithium-ion battery.

[0049] In Examples 2-28, only the preparation of the negative active material is different, and the method of preparing the positive electrode sheet and the battery is the same as in Example 1. Only the differences are described below. In Examples 2-5, the proportion of the discharge 0.17V capacity in Example 1 is selected as 35%, 45%, 55%, and 65%, respectively. In Examples 6-10, the proportion of the discharge 0.17V capacity in Example 1 is selected as 50%, and the proportion of the charge 0.4V capacity is selected as 35%, 45%, 55%, 65%, and 75%, respectively. In Examples 11-15, the proportion of the discharge 0.17V capacity in Example 1 is selected as 50%, and the discharge capacity is selected as 1800mAh / g, 2000mAh / g, 2200mAh / g, 2400mAh / g, and 2600mAh / g, respectively. In Examples 16-19, the proportion of the discharge 0.17V capacity in Example 1 is selected as 50%, and the doping element is changed to lithium, magnesium, titanium, and aluminum, respectively. In Examples 20-23, the proportion of the discharge 0.17V capacity in Example 1 is selected as 50%, and the I2 / I1 value is selected as 0.41, 0.64, 1, and 2.5, respectively. In Examples 24-28, the proportion of the discharge 0.17V capacity in Example 1 is selected as 50%, and the average particle size value is selected as 0.1μm, 0.5μm, 5μm, 20μm, and 30μm, respectively, and the corresponding specific surface area is 80m 2 / g, 30m 2 / g, 10m 2 / g, 1m 2 / g, 0.5m 2 / g.

[0050] The various performance test methods of the present disclosure are described below.

[0051] Specific surface area test:

[0052] At a constant low temperature, the amount of gas adsorbed on the surface of a solid at different relative pressures is determined, and then the monolayer adsorption amount of the sample is obtained based on the Brunauer-Emmett-Teller adsorption theory and its formula, so as to calculate the specific surface area of the solid.

[0053] BET formula:

[0054] Wherein: W - the mass of the gas adsorbed by the solid sample at a relative pressure

[0055] Wm - the saturated adsorption amount of a gas that covers a monolayer

[0056] Slope: (c-1) / (WmC), intercept: 1 / WmC, total specific surface area: (Wm*N*Acs / M)

[0057] Specific surface area: S = St / m, where m is the mass of the sample, Acs: the average area occupied by each N2 molecule is 16.2 A 2 .

[0058] 1.5-3.5 g of the powder sample was weighed into the test sample tube of the TriStar II 3020, and the test was performed after degassing at 200°C for 120 min.

[0059] Particle size test:

[0060] 0.02 g of the powder sample was added to a 50 ml clean beaker, 20 ml of deionized water was added, and a few drops of 1% surfactant were added to completely disperse the powder in the water. Ultrasonic cleaning was performed in a 120 W ultrasonic cleaner for 5 min, and the particle size distribution was tested using a MasterSizer 2000.

[0061] X-ray diffraction (XRD) test:

[0062] 1.0-2.0 g of the sample was weighed into the groove of the glass sample holder, and a glass sheet was used to compact and flatten it. The test was performed according to JJS K 0131-1996 "General methods for X-ray diffraction analysis" using an X-ray diffractometer (Bruker, D8), with a test voltage of 40 kV, a current of 30 mA, a scanning angle range of 10°-85°, a scanning step of 0.0167°, and a time setting of 0.24 s for each step. The XRD diffraction pattern was obtained, and from the pattern, the 2θ value corresponding to the highest intensity I1 at 28.4° and the highest intensity I2 at 21.0° were obtained, and the ratio of I2 / I1 was calculated.

[0063] Battery charge and discharge test method:

[0064] The negative electrode material obtained in the examples, conductive carbon black, and adhesive polyacrylic acid were mixed in a mass ratio of 80:10:10 with deionized water to form a slurry, which was coated with a doctor blade to a thickness of 100 μm. The coated sample was dried in a vacuum drying oven at 85°C for 12 hours, and then cut into a circular sheet with a diameter of 1 cm using a punch press in a dry environment. A lithium metal sheet was used as the counter electrode in a glove box, and a ceglard composite membrane was used as the separator membrane. The electrolyte was added to assemble a button cell. The button cell was tested for charge and discharge capacity using a LAND series battery tester.

[0065] Charge-discharge procedure: discharge at 0.05C constant current until the potential of the electrode reaches 0.005V, then discharge at 0.01C constant current until the potential of the electrode reaches 0.005V, after 10min rest, discharge at 0.002C constant current until the potential of the electrode reaches 0.005V. After 10min rest, charge at 0.05C constant current until the potential of the electrode reaches 2.0V.

[0066] First efficiency test:

[0067] The negative electrode material, conductive carbon black and binder polyacrylic acid (PAA) were mixed with deionized water in a mass ratio of 80:10:10 to form a slurry, which was coated with a doctor blade to a thickness of 100 um. The coated electrode was dried in a vacuum oven at 85°C for 12 hours. The dried electrode was then punched into a 1 cm diameter disc using a punch press in a dry environment. The disc was assembled into a coin cell battery using lithium metal as the counter electrode, a ceglard composite separator, and an electrolyte. The charge-discharge performance of the battery was tested using a LAND battery tester.

[0068] First, discharge at 0.05C to 0.005V, rest for 5 minutes, then discharge at 50μA to 0.005V, rest for 5 minutes, then discharge at 10μA to 0.005V, to obtain the first lithium intercalation capacity of the material. Then charge at 0.1C to 2V to obtain the first lithium extraction capacity. Finally, the first efficiency of the material is obtained by dividing the first lithium extraction capacity by the first lithium intercalation capacity.

[0069] Cycle performance test:

[0070] The test temperature was 25°C / 45°C. The battery was charged at 0.7C constant current to 4.4V, then charged at constant voltage to 0.025C, and then discharged at 0.5C to 3.0V after 5 minutes of rest. The capacity obtained in this step was taken as the initial capacity. The battery was cycled at 0.7C charge / 0.5C discharge. The capacity decay curve was obtained by comparing the capacity of each step with the initial capacity. The number of cycles at 25°C until the capacity retention rate reached 80% was taken as the room temperature cycle performance of the electrode assembly, and the number of cycles at 45°C until the capacity retention rate reached 80% was taken as the high temperature cycle performance of the electrode assembly. The cycle performance of the material was obtained by comparing the cycle numbers in the above two cases.

[0071] Swelling rate test of electrode assembly:

[0072] The thickness of the fresh electrode assembly at half charge was tested using a screw micrometer. After cycling to 400 cycles, the thickness of the electrode assembly at that time was tested again using a screw micrometer. The swelling rate of the electrode assembly at that time was obtained by comparing the thickness of the fresh electrode assembly at half charge.

[0073] The various parameters and results of the test cells and the full cell electrochemical devices are described below.

[0074] Table 1 shows the parameter settings of the test cells of Examples 1 to 5, and Table 2 shows the cycle performance and expansion rate of the corresponding electrochemical devices.

[0075] Table 1

[0076]

[0077] Table 2

[0078]

[0079] By comparing Examples 1 to 5, it is found that the higher the proportion of the discharge capacity of the silicon-based material negative electrode at the potential of 0.17 V to the initial discharge capacity of the test cell, the better the cycle performance of the silicon-based material at normal and high temperatures in the electrochemical device (full cell), and the lower the expansion rate of the electrode assembly. This is because the higher the proportion, the closer the silicon-based material is to the characteristics of amorphous silicon-based material, i.e., the smaller the degree of disproportionation of the silicon compound, so that the expansion and contraction of the silicon-based material caused by charging and discharging can be suppressed more, thereby effectively improving the cycle performance of the electrochemical device and reducing the expansion rate. In addition, due to the limitation of the characteristics of the silicon-based material, the proportion has an upper limit of 65%.

[0080] Table 3 shows the parameter settings of the test cells of Examples 6 to 10, and Table 4 shows the cycle performance and expansion rate of the corresponding electrochemical devices.

[0081] Table 3

[0082]

[0083] Table 4

[0084]

[0085] By comparing Examples 6 to 10, it is found that the lower the proportion of the charge capacity of the silicon-based material negative electrode at the potential of 0.4 V to the initial charge capacity of the test cell, the better the cycle performance of the silicon-based material at normal and high temperatures in the electrochemical device, and the lower the expansion rate of the electrode assembly. This is because the lower the proportion, the closer the silicon-based active material is to the characteristics of amorphous silicon-based material, i.e., the smaller the degree of disproportionation of the silicon compound, so that the expansion and contraction of the silicon-based material caused by charging and discharging can be suppressed more, thereby effectively improving the cycle performance of the electrochemical device and reducing the expansion rate. In addition, due to the limitation of the characteristics of the silicon-based material, the proportion has a lower limit of 35%.

[0086] Table 5 shows the parameter settings of the test batteries of Examples 11-15, and Table 6 shows the cycle performance and expansion rate of the corresponding electrochemical devices.

[0087] Table 5

[0088]

[0089] Table 6

[0090]

[0091] By comparing Examples 11-15, it can be seen that the higher the initial discharge capacity of the test battery, the less the amount of surface lithium doping, so the lower the initial efficiency and the higher the expansion rate; the lower the initial discharge capacity of the test battery, the more the amount of surface lithium doping, so the higher the initial efficiency and the lower the expansion rate.

[0092] When the initial discharge capacity of the test battery is too low, it means too much lithium doping amount, which will cause the gelation of the slurry, thereby reducing the cycle performance of the negative electrode material; and when the initial discharge capacity of the test battery is too high, too little lithium doping amount and too low initial efficiency will cause poor cycle performance. Therefore, the initial discharge capacity of the test battery is set in the range of 2000 mAh / g-2400 mAh / g. Figure 3 The charge-discharge curve of the silicon-based material in Example 13 of the present disclosure in the test battery is shown.

[0093] Table 7 shows the parameter settings of the test batteries of Examples 16-19, and Table 8 shows the cycle performance and expansion rate of the corresponding electrochemical devices.

[0094] Table 7

[0095]

[0096] Table 8

[0097]

[0098] Doping at least one of Li, Mg, Ti or Al elements in the silicon-based material helps to improve the cycle performance and expansion rate of the prepared electrochemical device. By comparing Examples 16-19, it can be seen that under the condition of other conditions being the same, the type of metal element doped in the negative electrode material has certain influence on the cycle performance and expansion rate of the electrochemical device, but the difference is not big.

[0099] Table 9 shows the parameter settings of the test batteries of Examples 20-23, and Table 10 shows the cycle performance and expansion rate of the corresponding electrochemical devices.

[0100] Table 9

[0101]

[0102] Table 10

[0103]

[0104] As can be seen by comparing Examples 20-23, as the value of I2 / I1increases, the cycle performance of the electrochemical device decreases and the expansion rate increases. The value of I2 / I1reflects the degree to which the silicon-based material is affected by disproportionation, and the greater the value, the greater the size of the silicon nanocrystals produced by disproportionation of SiO within the silicon-based material, which can cause a sharp increase in stress in localized areas during lithium intercalation, leading to structural damage to the negative electrode material during cycling, which can result in a decrease in cycle performance and an increase in expansion rate of the electrochemical device. Figure 4 X-ray diffraction patterns of the silicon-based material particles in Example 20 of the present disclosure are shown.

[0105] Table 11 shows the parameter settings for the test batteries of Examples 24-28, and Table 12 shows the cycle performance and expansion rate of the corresponding electrochemical devices.

[0106] Table 11

[0107]

[0108] Table 12

[0109]

[0110] As can be seen by comparing Examples 24-28, as the average particle size of the silicon-based material particles increases and the specific surface area decreases, the cycle performance and expansion rate of the electrochemical device first improves and then deteriorates. This is because when the average particle size of the silicon-based material is large, the silicon-based material particles are under a large stress and are prone to breakage, and the consumption of electrolyte by the constant generation of fresh surfaces can result in poor cycle performance and expansion rate of the electrochemical device. When the average particle size of the silicon-based material is small, the large specific surface area can increase side reactions, which can deteriorate the cycle performance and expansion rate of the electrochemical device.

[0111] The above description is merely that of the preferred embodiments of the present disclosure and of the principles thereof. It will be appreciated that the scope of the disclosure is not limited to the specific combinations of technical features disclosed herein, and should also encompass other technical solutions formed by any combination of the technical features disclosed above or their equivalent features, without departing from the above disclosed concept. For example, technical solutions formed by replacing the above features with technical features having similar functions disclosed in the present disclosure.

Claims

1. A negative electrode material, comprising: a silicon-based material, wherein a test battery comprising an electrode containing the negative electrode material combined with a counter electrode composed of metallic lithium has a first efficiency of 82.9%to 86%, and wherein a discharge capacity of the electrode in the test battery at a potential of 0.17V is in a range of 35%to 65%of a first discharge capacity of the test battery; a particle of the silicon-based material has a first peak intensity I1belonging to a range of 20.5°to 21.5° and a second peak intensity I2belonging to a range of 28.0°to 29.0° in a diffraction pattern of an X-ray diffraction test, wherein 0< I2 / I1≤1; The silicon-based material includes M y SiO x , 0≤y≤4, 0≤x≤4, and M includes at least one of Li, Mg, Ti, or Al. wherein the first efficiency is tested in the following manner: the negative electrode material, conductive carbon black, and a binder polyacrylic acid are mixed with deionized water in a mass ratio of 80:10:10 to form a slurry, a coating layer with a thickness of 100μm is obtained using a doctor blade, the coating layer is dried in a vacuum drying oven at 85℃ for 12 hours, and then the coating layer is cut into a disc with a diameter of 1cm in a dry environment using a punch press, a lithium metal sheet is used as a counter electrode in a glove box, a celgard composite film is selected as a separator film, and a coin cell is assembled by adding an electrolyte; a battery test system of blue electric series is used to test the coin cell to test its charge and discharge performance: first, 0.05C is discharged to 0.005V, then 50μA is discharged to 0.005V after 5 minutes of static, and then 10μA is discharged to 0.005V after another 5 minutes of static, to obtain a first lithium intercalation capacity of the negative electrode material; then, 0.1C is charged to 2V to obtain a first lithium extraction capacity; finally, the first lithium extraction capacity is divided by the first lithium intercalation capacity to obtain the first efficiency.

2. The negative electrode material of claim 1, wherein, a charge capacity of the electrode in the test battery at a potential of 0.4V is in a range of 35%to 65%of a first charge capacity of the test battery.

3. The negative electrode material of claim 1, wherein, the first discharge capacity of the test battery is in a range of 2000mAh / g to 2400mAh / g.

4. The negative electrode material of claim 1, wherein, an average particle size of the silicon-based material is 0.5μm to 20μm.

5. The negative electrode material of claim 1, wherein, The specific surface area of the silicon-based material is 1 m 2 / g ~ 30 m 2 / g. 6.A negative electrode sheet, comprising: a current collector; an active material layer on the current collector; wherein the active material layer comprises the negative electrode material according to any one of claims 1 to 5. 7.An electrochemical device, comprising: a positive electrode sheet; a negative electrode sheet; a separator film disposed between the positive electrode sheet and the negative electrode sheet; wherein the negative electrode sheet is the negative electrode sheet according to claim 6. 8.An electronic device comprising the electrochemical device according to claim 7.

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