WO2021189349A1 - 负极材料、负极极片、包含该负极极片的电化学装置及电子装置 - Google Patents

负极材料、负极极片、包含该负极极片的电化学装置及电子装置 Download PDF

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WO2021189349A1
WO2021189349A1 PCT/CN2020/081370 CN2020081370W WO2021189349A1 WO 2021189349 A1 WO2021189349 A1 WO 2021189349A1 CN 2020081370 W CN2020081370 W CN 2020081370W WO 2021189349 A1 WO2021189349 A1 WO 2021189349A1
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particles
silicon
negative electrode
electrode material
graphite particles
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PCT/CN2020/081370
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English (en)
French (fr)
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廖群超
崔航
谢远森
王超
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宁德新能源科技有限公司
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Priority to PCT/CN2020/081370 priority Critical patent/WO2021189349A1/zh
Priority to EP20926853.1A priority patent/EP4131484A4/en
Priority to CN202080092381.4A priority patent/CN114982009B/zh
Publication of WO2021189349A1 publication Critical patent/WO2021189349A1/zh
Priority to US17/952,646 priority patent/US20230034617A1/en

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Definitions

  • silicon-based materials can significantly increase the energy density of batteries.
  • silicon-oxygen materials in silicon-based materials have the advantages of high specific capacity (2400mAh/g), abundant sources of raw materials, and environmental friendliness.
  • the mixed negative electrode made of silicon-oxygen material has large volume expansion and contraction during the process of deintercalating lithium, which leads to the continuous migration of silicon-oxygen material particles, which increases the porosity of the negative electrode and makes the active material therein. The failure of the connection between the batteries increases the capacity decay rate and deformation rate of the battery, and seriously affects its effect in practical applications.
  • Another object of the present invention is to provide a negative pole piece including the above-mentioned negative electrode material and a preparation method thereof, a lithium ion secondary battery and a preparation method thereof, an electrochemical device, and an electronic device.
  • the present invention provides a negative electrode material comprising silicon-based particles and graphite particles.
  • a negative electrode material comprising silicon-based particles and graphite particles.
  • Dv50 is the particle size corresponding to when the cumulative volume fraction of particles in the volume-based distribution reaches 50%
  • Dn50 is the particle size corresponding to when the cumulative number fraction of particles in the number-based distribution reaches 50%.
  • the value of Dn50/Dv50 is the ratio of Dn50 to Dv50 obtained by the laser scattering particle size analyzer. The closer the value is to 1, the more concentrated the particle size distribution; in the anode material provided by the present invention, when the distribution of graphite particles is concentrated When the distribution concentration of silicon-based particles is lower than that of silicon-based particles, the battery has better cycle performance and lower deformation rate. This is because the lithium-intercalation expansion of silicon-based materials is much greater than that of graphite materials. In order to reduce the stress generated during expansion, silicon-based particles The average particle size of the graphite particles is smaller than that of the graphite particles.
  • the active material on the pole piece is composed of silicon-based particles and graphite particles
  • the distribution of silicon-based particles is more concentrated than that of graphite particles. Its expansion has the least effect on the overall expansion of the pole piece, improving its contact with graphite particles during cycling, thereby improving the battery's cycle performance and the rate of deformation (Swelling).
  • the electrical performance of the battery is better.
  • the value of Dn50/Dv50 of graphite particles is less than 0.1, there are too many fine particles and too many large particles in the graphite particles; too many fine particles cause the material specific surface area to be too large, reducing the first efficiency; too much large particles will increase the lithium ion The transmission distance will aggravate the deformation of the battery and deteriorate the rate performance of the battery.
  • the Dn50/Dv50 value of the graphite particles is greater than 0.65, the particle size distribution of the graphite particles is too concentrated, which is not conducive to its accumulation in the negative electrode sheet, and the processing cost is significantly increased.
  • the electrical performance of the battery is better.
  • the Dn50/Dv50 value of the silicon-based particles is less than 0.3, the distribution and concentration of the silicon-based particles are poor, and there are a large number of silicon-based particles that are too large or too small in size. Too many silicon-based particles with too small particle size will increase the contact area with the electrolyte, produce more solid electrolyte interface membranes (SEI membranes), and consume the limited reversible lithium in the battery.
  • SEI membranes solid electrolyte interface membranes
  • the average sphericity D of the silicon-based particles is greater than or equal to 0.8.
  • the general formula of the silicon-based particles is: SiO x C y M z (I), where 0 ⁇ x ⁇ 2, 0 ⁇ y ⁇ 1, 0 ⁇ z ⁇ 0.5, M includes at least one of lithium, magnesium, titanium, or aluminum.
  • a carbon film, a polymer film or a composite film of the two are present on the surface of the graphite particles.
  • the mass of the coating film of the silicon-based particles accounts for 0.1-10% of the total mass of the silicon-based particles.
  • the negative electrode material of the present invention it is preferred that in the XRD diffraction pattern of the silicon-based particles, when 2 ⁇ is attributable to 20.5°-21.5°, the highest intensity value is I1, and 2 ⁇ attributable to 28.0°-29.0° is the highest When the value of intensity is I2, I2/I1 ⁇ 10 is satisfied, and I2/I1 ⁇ 1 is more preferable.
  • the specific surface area of the silicon-based particles is 0.1-50 m 2 /g, more preferably 0.1-5 m 2 /g.
  • the negative electrode material according to the present invention preferred is the Raman scattering peak of the graphite particles, when the peak intensity at 1330cm -1 to the peak intensity I1580 is I1330,1580cm -1 at the time, satisfies the following Conditional expression (5):
  • the graphite particles include secondary particles, and the secondary particles account for more than 70% by weight of the total amount of the graphite particles.
  • the present invention also provides a negative pole piece, which includes the above-mentioned negative electrode material.
  • the present invention also provides a method for preparing a negative pole piece, which includes the following steps:
  • the content of silicon-based particles in the first mixture is 5-30 wt%
  • the content of conductive agent is 0.5-5 wt%
  • the balance is graphite particles.
  • the conductive agent includes at least one of nano conductive carbon black, carbon nanotube, carbon fiber, flake graphite, graphene or Ketjen black.
  • the carbon nanotubes include single-walled carbon nanotubes, multi-walled carbon nanotubes, or a combination of the two; the carbon fibers include vapor-grown carbon fibers, carbon nanofibers, or a combination of both. combination.
  • the binder includes polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, carboxymethyl cellulose At least one of sodium methylcellulose, polyimide, polyamideimide, styrene butadiene rubber, or polyvinylidene fluoride.
  • the thickness of the active layer of the negative electrode sheet is 50-200 ⁇ m
  • the single-sided compaction density of the active layer is 1.4-1.9 g/cm 3
  • the porosity of the active layer is 15- 35%.
  • the present invention also provides a lithium ion secondary battery, which includes: a positive pole piece, the above-mentioned negative pole piece, a separator, and an electrolyte.
  • the present invention also provides a method for preparing a lithium ion secondary battery, which includes the following steps:
  • the conductive agent in step S1 includes at least one of nano-conductive carbon black, carbon nanotube, carbon fiber, flake graphite, graphene or Ketjen black.
  • the isolation membrane is made of at least one of glass fiber, polyester, polyethylene, polypropylene or polytetrafluoroethylene; the isolation membrane is a porous polymer film , Wherein the diameter of the hole is 0.01 ⁇ m-1 ⁇ m; the thickness of the isolation membrane is 5 ⁇ m-500 ⁇ m.
  • the organic lithium salt includes lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide , At least one of lithium bisoxalate borate or lithium difluorooxalate borate.
  • the present invention also provides an electrochemical device, the electrochemical device comprising: the above-mentioned negative pole piece.
  • Example 2 is a particle size distribution diagram of SiO particles and graphite particles in Example 1 of the present invention
  • Figure 3 is an XRD diagram of SiO in Example 12 of the present invention.
  • Example 4 is an XRD pattern of SiO in Example 14 of the present invention.
  • Fig. 5 is a comparison diagram of deformation performance between Example 3 and Comparative Example 1 of the present invention.
  • the negative electrode material provided by the present invention comprises silicon-based particles and graphite particles.
  • the Dn50/Dv50 value of the graphite particles is A
  • the Dn50/Dv50 value of the silicon-based particles is B
  • the following conditional formula is satisfied (1) to (3):
  • Dv50 is the particle size corresponding to when the cumulative volume fraction of particles in the volume-based distribution reaches 50%
  • Dn50 is the particle size corresponding to when the cumulative number fraction of particles in the number-based distribution reaches 50%.
  • the value of Dn50/Dv50 is the ratio of Dn50 to Dv50 measured by a laser scattering particle size analyzer. The closer the value is to 1, the more concentrated the particle size distribution.
  • composite anode materials containing silicon-based particles and graphite particles when graphite When the distribution concentration of particles is lower than that of silicon-based particles, the battery has better cycle performance and lower deformation rate. This is because the lithium-intercalation expansion of silicon-based materials is much greater than that of graphite materials, in order to reduce the expansion Stress, the average particle size of silicon-based particles is smaller than the average particle size of graphite particles.
  • the active material on the pole piece is composed of silicon-based particles and graphite particles
  • the distribution of silicon-based particles is more concentrated than graphite particles, which facilitates the dispersion in graphite particles.
  • its expansion has the least influence on the overall expansion of the pole piece, and improves the contact with the graphite particles during the cycle, thereby improving the cycle performance of the battery and reducing the deformation rate.
  • the electrical performance of the battery is optimal; when the value of Dn50/Dv50 of graphite particles is less than 0.1, there are fine particles and too many large particles in the graphite particles. ; When there are too many fine particles, the specific surface area of the material is too large, which reduces the initial efficiency; when there are too many large particles, the transmission distance of lithium ions is increased, and the deformation rate and rate performance of the battery are deteriorated. Moreover, when the Dn50/Dv50 value of the graphite particles is greater than 0.65, the particle size distribution of the graphite particles is too concentrated, which is not conducive to their accumulation in the negative electrode sheet, and the processing cost is significantly increased.
  • the excessively large size of silicon-based particles not only increases the stress generated during the expansion of lithium insertion, which leads to cracking of the silicon-based particles, exposing the fresh interface and reacting with the electrolyte, consuming reversible lithium, and deteriorating the cycle performance; at the same time, silicon with an excessively large particle size
  • the base particles increase the diffusion path of lithium ions, increase the concentration polarization, and affect the rate performance of the battery.
  • the Dn50/Dv50 value of the silicon-based particles is greater than 0.85, the production yield is low, the cost is high, and it is difficult to apply on a large scale.
  • the average sphericity C of the graphite particles is between 0.55 and 0.75, such as but not limited to 0.55, 0.65, 0.75.
  • the general formula of the silicon-based particles is: SiO x C y M z (I), where 0 ⁇ x ⁇ 2, 0 ⁇ y ⁇ 1, 0 ⁇ z ⁇ 0.5, and M includes lithium, At least one of magnesium, titanium, or aluminum.
  • SiO X 0.5 ⁇ x ⁇ 1.5
  • SiOxCy 0.5 ⁇ x ⁇ 1.5
  • 0 ⁇ y ⁇ 0.1 SiOxCyLiz
  • the carbon coating is formed of at least one of shaped carbon, carbon nanotubes, carbon nanoparticles, vapor-deposited carbon fibers, or graphene.
  • the polymer coating is made of polyvinylidene fluoride and its derivatives, carboxymethyl cellulose and its derivatives, polyvinylpyrrolidone and its derivatives, polyacrylic acid and its derivatives, or polybutylene styrene. At least one of rubber is formed.
  • a derivative refers to a more complex product derived from the substitution of hydrogen atoms or atomic groups in a simple compound by other atoms or atomic groups. For example but not limited to sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium polyacrylate, ammonium polyacrylate.
  • the thickness of the coating film of the silicon-based particles is 0.5-50 nm, such as but not limited to 0.5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm.
  • the mass of the coating of the silicon-based particles accounts for 0.1-10% of the total mass of the silicon-based particles, such as but not limited to 0.1%, 3%, 5%, 8%, 10%.
  • the value of 2 ⁇ attributable to the highest intensity of 20.5°-21.5° is I1
  • the value of 2 ⁇ attributable to 28.0°-29.0° of the highest intensity is I2
  • I2/I1 ⁇ 10 such as but not limited to 10, 5, 2, 1, and I2/I1 ⁇ 1 is more preferred.
  • the specific surface area of the silicon-based particles is 0.1-50m 2 /g, such as but not limited to 0.1m 2 /g, 5m 2 /g, 10m 2 /g, 20m 2 /g, 30m 2 /g g, 40 m 2 /g, 50 m 2 /g, more preferably 0.1 to 5 m 2 /g.
  • the Raman scattering peak of the graphite particles when the peak intensity at 1330cm -1 to the peak intensity I1580 is I1330,1580cm -1 at the time, satisfies the following conditional formula (5):
  • the graphite particles include secondary particles, and the secondary particles account for more than 70% by weight of the total amount of graphite particles. In other embodiments, the graphite particles are composed of more than 70% by weight of secondary particles and the balance of primary particles.
  • the negative pole piece provided by the present invention is coated with the above negative electrode material.
  • the coating method should just follow the conventional electrode material coating method, which is not limited in the present invention.
  • the content of silicon-based particles is 5-30 wt%
  • the content of the conductive agent is 0.5-5 wt%
  • the balance is graphite particles.
  • the first mixture includes 5 wt% silicon-based particles, 0.5 wt% conductive agent, and the balance is graphite particles; in some embodiments, the first mixture includes 30 wt% silicon-based particles, 0.5 wt% conductive agent, The balance is graphite particles; in some embodiments, the first mixture contains 30 wt% silicon-based particles, 5 wt% conductive agent, and the balance is graphite particles; in some embodiments, the first mixture contains 15 wt% silicon-based particles, 2.5 wt% wt% conductive agent, the balance is graphite particles.
  • the conductive agent includes at least one of nano conductive carbon black, carbon nanotubes, carbon fibers, flake graphite, graphene, or Ketjen black.
  • the weight ratio of the first mixture to the binder is 100:1-6, such as but not limited to 100:1, 100:6, 100:3.
  • the binder includes polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, poly At least one of imide, polyamideimide, styrene butadiene rubber, or polyvinylidene fluoride.
  • the solvent includes at least one of deionized water and N-methylpyrrolidone.
  • the thickness of the active layer of the negative pole piece is 50-200 ⁇ m
  • the single-sided compaction density of the active layer is 1.4-1.9 g/cm 3
  • the porosity of the active layer is 15-35%.
  • the lithium ion secondary battery provided by the present invention includes: a positive pole piece, the above-mentioned negative pole piece, a separator, and an electrolyte.
  • the present invention also provides a method for preparing the above-mentioned lithium ion secondary battery, which includes the following steps:
  • step S2 the first positive electrode mixed slurry obtained in step S1 is coated on the current collector, and the positive electrode pieces are obtained after drying, cold pressing, and slitting;
  • the conductive agent in step S1 includes at least one of nano-conductive carbon black, carbon nanotubes, carbon fibers, flake graphite, graphene, or Ketjen black.
  • the electrolyte includes an organic solvent, a lithium salt, and additives
  • the lithium salt is an organic lithium salt and/or an inorganic lithium salt.
  • the organic solvent includes at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, propylene carbonate, or ethyl propionate.
  • the electrochemical device provided by the present invention includes: the above-mentioned negative pole piece.
  • the electronic device provided by the present invention includes: the above-mentioned lithium ion secondary battery and/or electrochemical device.
  • Observation of powder particle micro-morphology Use scanning electron microscope to observe the powder micro-morphology to characterize the surface coating of the material.
  • the selected test instrument is: OXFORD EDS (X-max-20mm 2 ), the acceleration voltage is 15KV, and the focus is adjusted.
  • the observation magnification is from 50K for high magnification observation, and for low magnification, 500-2000 is mainly used to observe particle agglomeration.
  • Sphericity test use Malvern automatic image particle size analyzer to capture and process a certain number of dispersed particles (greater than 5000), and then use image-directed Raman spectroscopy (MDRS) to accurately analyze the microstructure and morphology of the particles , Get the longest diameter and shortest diameter of all particles, calculate the ratio of shortest diameter/longest diameter to calculate the sphericity of the particles;
  • MDRS image-directed Raman spectroscopy
  • Specific surface area test At low temperature and constant temperature, the adsorption amount of gas on the solid surface at different relative pressures is measured, and then the adsorption amount of the sample monolayer is obtained based on the Brownauer-Ett-Taylor adsorption theory and the BET equation. In order to calculate the specific surface area of the solid.
  • Particle size test (the size of the particles is called “particle size”, also called “particle size” or “diameter”): add about 0.02g powder sample into a 50ml clean beaker, add about 20ml deionized water, and then drop Add a few drops of 1% surfactant to completely disperse the powder in the water. Ultrasound in a 120W ultrasonic cleaning machine for 5 minutes. Use the MasterSizer 2000 to test the particle size distribution. The laser scattering particle size analyzer is used to obtain the cumulative volume of the particles in the volume reference distribution. The diameter corresponding to when the score reaches 50%, and the diameter corresponding to the cumulative number of particles in the number basis distribution when the score reaches 50%.
  • XRD test Weigh 1.0-2.0g of the sample into the groove of the glass sample holder, and use a glass sheet to compact and smooth it, using an X-ray diffractometer (Brook, D8) in accordance with JJS K 0131-1996 " X-ray Diffraction Analysis General Principles" for testing, the test voltage is set to 40kV, the current is 30mA, the scanning angle range is 10-85°, the scanning step is 0.0167°, and the time set for each step is 0.24s.
  • the OI value of graphite is obtained by calculating the ratio of (004) peak and (110) peak intensity in the XRD diffraction peaks of graphite.
  • Powder material button battery test method the negative electrode material, conductive carbon black and binder PAA obtained in the example are mixed with deionized water according to the mass ratio of 80:10:10 to form a slurry, and the coating is 100um with a doctor blade. Thickness of the coating, after being dried in a vacuum drying oven at 85°C for 12 hours, it is cut into a disc with a diameter of 1cm using a punching machine in a dry environment. The metal lithium sheet is used as the counter electrode in the glove box, and the isolation membrane is ceglard. Composite membrane, adding electrolyte to assemble button cell. Use the LAND series battery test test to charge and discharge the battery to test its charge and discharge capacity.
  • using the first lithium removal capacity compared to the previous first lithium insertion capacity is the first efficiency of the material.
  • Cycle test Test temperature is 25 and 45°C, charge to 4.4V at 0.7C constant current, charge to 0.025C at constant voltage, and discharge to 3.0V at 0.5C after standing for 5 minutes.
  • the capacity obtained in this step is the initial capacity, and the 0.7C charge/0.5C discharge is carried out for a cycle test, and the capacity at each step is used as the ratio of the initial capacity to obtain the capacity attenuation curve.
  • the number of cycles from 25°C cycle to 90% of capacity retention is recorded as the room temperature cycle performance of the battery, and the number of cycles from 45°C cycle to 80% is recorded as the battery's high temperature cycle performance. By comparing the above two cases The number of cycles is used to obtain the cycle performance of the material.
  • Discharge rate test at 25°C, discharge to 3.0V at 0.2C, let stand for 5min, charge at 0.5C to 4.45V, charge at constant voltage to 0.05C, then stand for 5 minutes, adjust the discharge rate to 0.2 C, 0.5C, 1C, 1.5C, 2.0C discharge test, respectively obtain the discharge capacity, the capacity obtained under each rate is compared with the capacity obtained at 0.2C, and the rate performance is compared by comparing the ratio between 2C and 0.2C.
  • Battery full charge expansion rate test Use a spiral micrometer to test the thickness of a fresh battery when it is half-charged (a full battery charged to the interval between 3.7V and 4.0V is defined as a half-charged full battery, and this process is called a half-charge). At 400cls, when the battery is fully charged, use a spiral micrometer to test the thickness of the battery at this time, and compare it with the thickness of the fresh battery at the initial half-charge, to get the expansion rate of the fully charged battery at this time.
  • the first mixed slurry is coated on the current collector nickel foil, and the negative electrode is obtained after drying, cold pressing, and slitting.
  • the thickness of the active layer is 150 ⁇ m, and the single-sided compaction density of the active layer is 1.7g /cm 3 , the porosity of the active layer is 25%.
  • step (2) Combine the positive pole piece obtained in step (1), the above-mentioned negative pole piece and the separator polyethylene (PE) porous polymer film (the diameter of the hole is 0.01 micron-1 micron; the thickness of the separator film is 200 microns) Obtain bare cells by winding;
  • PE polyethylene
  • step (3) Put the bare cell obtained in step (2) into the aluminum plastic film of the battery bag, after drying, inject the electrolyte obtained in step (3) and encapsulate, after chemical conversion, the lithium ion secondary battery is obtained, that is, the full battery .
  • the negative electrode materials selected in this example and the performance evaluation results of the resulting full battery are shown in Table 1 (the gram capacity is the capacity obtained when the delithiation cut-off voltage is 2.0V, the same below) and Table 1-1.
  • Example 1 The differences from Example 1 are shown in Table 1.
  • the negative electrode materials selected in this example and the performance evaluation results of the resulting full battery are shown in Table 1 and Table 1-1.
  • Example 1 The differences from Example 1 are shown in Table 1.
  • the negative electrode materials selected in this example and the performance evaluation results of the resulting full battery are shown in Table 1 and Table 1-1.
  • Examples 1-3 satisfy: the Dn50/Dv50 value of graphite particles is in the range of 0.1-0.65, the Dn50/Dv50 value of silicon-based particles is in the range of 0.3-0.85, and the silicon-based particles The Dn50/Dv50 value of the graphite particles is greater than the Dn50/Dv50 value of the graphite particles, and the final full battery performance is excellent.
  • the performance of the full battery obtained in Comparative Example 1 which does not meet the above conditions is significantly inferior to the embodiment.
  • the deformation performance comparison diagram of Example 3 and Comparative Example 1 is shown in FIG. 5.
  • Example 2 The differences from Example 1 are shown in Table 2.
  • Example 4 The differences from Example 4 are shown in Table 2.
  • the negative electrode materials selected in this example and the performance evaluation results of the resulting full battery are shown in Table 2 and Table 2-1.
  • Examples 4-6 meet the following requirements: the Dn50/Dv50 value of graphite particles is in the range of 0.1-0.65, the Dn50/Dv50 value of silicon-based particles is in the range of 0.3-0.85, and the silicon-based particles The Dn50/Dv50 value of the graphite particles is greater than the Dn50/Dv50 value of the graphite particles, and the final full battery performance is excellent. However, the performance of the full battery obtained in Comparative Example 2-3, which does not meet the above conditions, is significantly inferior to the embodiment.
  • the active material on the pole piece is composed of silicon-based particles and graphite particles
  • the distribution of silicon-based particles is more concentrated than that of graphite particles, which is beneficial to disperse in the gaps where graphite particles are stacked, so that its expansion has the smallest effect on the overall expansion of the pole piece.
  • the larger the Dn50/Dv50 value of SiO particles the better the battery cycle and deformation performance when matched with the same graphite. This is due to the poor distribution and concentration of silicon-based particles. As a result, the contact area with the electrolyte is increased, more SEI layers are produced, and the electrolyte and the limited reversible lithium in the battery are consumed.
  • Example 3 The differences from Example 1 are shown in Table 3. This embodiment selected anode material and the performance evaluation results of the resulting full cell in Tables 3 and 3-1, wherein I1330, I1580 refers to Raman scattering peak corresponding to graphite particles or SiO particles 1330cm -1, 1580cm -1 The intensity of the peak at.
  • Example 7 The differences from Example 7 are shown in Table 3.
  • the negative electrode materials selected in this example and the performance evaluation results of the resulting full battery are shown in Table 3 and Table 3-1.
  • Example 7 The difference from Example 7 is shown in Table 5, where I1 is the highest intensity value of 2 ⁇ attributable to 20.5°-21.5° from the XRD diffraction pattern of the corresponding SiO particle, and I2 is the highest intensity value of the corresponding SiO particle from the XRD diffraction pattern attributable to The highest intensity value of 28.0°-29.0°.
  • the negative electrode materials selected in this example and the performance evaluation results of the resulting full battery are shown in Table 5 and Table 5-1.
  • the XRD patterns of the SiO particles in Examples 12 and 14 are shown in Figs. 3 and 4.
  • Example 7 The differences from Example 7 are shown in Table 5.
  • the negative electrode materials selected in this example and the performance evaluation results of the resulting full battery are shown in Table 5 and Table 5-1.
  • I 2 /I 1 reflects the degree to which SiO particles are affected by disproportionation. The larger the value, the larger the size of the nano-silicon grains produced by disproportionation inside the SiO particles, which will cause local stress during the lithium insertion process. The sharp increase results in the destruction of the negative pole piece structure during the material cycle. In addition, due to the generation of nanocrystalline distribution, it affects the ability of grain boundary diffusion in the ion diffusion process.
  • Example 7 The difference from Example 7 is shown in Table 6, where D refers to the peak intensity of the Raman scattering peak of graphite particles at 1330 cm -1 , and G refers to the peak intensity of the Raman scattering peak of graphite particles at 1580 cm -1 .
  • the negative electrode materials selected in this example and the performance evaluation results of the resulting full battery are shown in Table 6 and Table 6-1.
  • Example 15 The differences from Example 15 are shown in Table 6.
  • the negative electrode materials selected in this example and the performance evaluation results of the resulting full battery are shown in Table 6 and Table 6-1.
  • Example 1 The difference from Example 1 is that there is a coating on the surface of the SiO particles.
  • the types of metal elements, the content of metal elements and the carbon content in the coating are shown in Table 7 (where "-" means that the substance is not added).
  • the thickness of the coating is 10 nm, and the mass of the coating is 0.425% of the total mass of the SiO particles.
  • Example 18 The differences from Example 18 are shown in Table 7.
  • the negative electrode materials selected in this example and the performance evaluation results of the resulting full battery are shown in Table 7 and Table 7-1.

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Abstract

一种负极材料，该负极材料包含硅基颗粒和石墨颗粒，当所述石墨颗粒的Dn50/Dv50值为A，所述硅基颗粒的Dn50/Dv50值为B时，满足下述条件式(1)至(3)：0.1≤A≤0.65(1)，0.3≤B≤0.85(2)，并且，B>A(3)，其中，Dv50为颗粒在体积基准分布中累计体积分数达到50％时所对应的粒径；Dn50为颗粒在数量基准分布中累计数量达到50％时所对应的粒径。还提供一种负极极片，以及包含该负极极片的锂离子二次电池或电化学装置，以及包含该锂离子二次电池和/或该电化学装置的电子装置。

Description

负极材料、负极极片、包含该负极极片的电化学装置及电子装置 技术领域
本发明属于电池技术领域，尤其涉及锂离子电池技术领域，具体涉及一种负极材料、涂覆有该负极材料的负极极片、以及包含该负极极片的电化学装置以及电子装置。
背景技术
硅基材料作为下一代高容量负极材料，可以显著提升电池的能量密度。尤其是硅基材料中的硅氧材料具有比容量高(2400mAh/g)、原料来源丰富、对环境友好等优势。然而，由硅氧材料制备的混合负极，在脱嵌锂过程中存在较大的体积膨胀和收缩，导致硅氧材料颗粒不断发生迁移，增大了负极极片的孔隙率，使其中的活性材料之间的连接失效，提高电池的容量衰减速率和变形率，严重影响其在实际应用中的效果。
现有针对提升电池循环和降低电池变形的技术主要集中在对硅基材料结构和界面的改善，并能取得较好的改善效果。然而，单纯地改善硅基材料而忽略了混合负极中石墨材料与其在形貌和粒径的合理搭配，并不能将负极电性能发挥到最佳。研究发现不同形貌和粒径的石墨颗粒与硅基材料搭配制备的负极有显著的区别，其主要表现在硅基材料的分布以及极片孔隙率和孔隙的分布，这对于电池的循环性能和变形有重大影响。
发明内容
针对现有技术中的上述问题，本发明的目的之一在于提供一种负极材料，从硅基材料和石墨材料之间形貌和粒径的合理匹配出发，来改善电池的 循环性能和变形率；并且，在硅基材料和石墨材料合理匹配的基础上，进一步限定硅基颗粒和石墨颗粒的粒径分布、球形度、XRD特性等特征，得到性能更优的负极材料。
本发明的另一目的还在于提供一种包括上述负极材料的负极极片及其制备方法、一种锂离子二次电池及其制备方法、一种电化学装置以及一种电子装置。
为此，本发明提供一种负极材料，该负极材料包含硅基颗粒和石墨颗粒，当所述石墨颗粒的Dn50/Dv50值为A，所述硅基颗粒的Dn50/Dv50值为B时，满足下述条件式(1)至(3)：
0.1≤A≤0.65       (1)，
0.3≤B≤0.85       (2)，
并且，B>A          (3)，
其中，Dv50为颗粒在体积基准分布中累计体积分数达到50％时所对应的粒径；Dn50为颗粒在数量基准分布中累计数量分数达到50％时所对应的粒径。
其中，Dn50/Dv50值为通过激光散射粒度仪测试得到的Dn50与Dv50的比值，其数值越趋近于1，颗粒粒度分布越集中；本发明提供的负极材料中，当石墨颗粒的分布集中程度低于硅基颗粒的分布集中程度时，电池的循环性更好以及变形率更低，这是由于硅基材料的嵌锂膨胀远大于石墨材料，为了减小膨胀时产生的应力，硅基颗粒的平均粒径小于石墨颗粒的平均粒径，当极片上活性物质由硅基颗粒和石墨颗粒复合组成时，硅基颗粒较石墨颗粒分布更为集中有利于分散在石墨颗粒堆积的缝隙中，使其膨胀对极片的整体膨胀影响最小，改善其循环中与石墨颗粒的接触，从而改善电池的循环性能以及变形率(Swelling)。
具体的，当石墨颗粒的Dn50/Dv50值在0.1-0.65范围内时，电池的电性能较优。当石墨颗粒的Dn50/Dv50的值小于0.1时，石墨颗粒中存在细小颗粒和大颗粒过多；细小颗粒过多导致材料比表面积过大，降低首次效率；大颗粒过多会增加了锂离子的传输距离，会加剧电池的变形，恶化电池的倍率性能。当石墨颗粒的Dn50/Dv50值大于0.65时，石墨颗粒的粒径分布过于集中，不利于其在负极极片中的堆积，且加工成本显著增加。
具体的，当硅基颗粒的Dn50/Dv50值在0.3-0.85范围内时，电池的电性能较优。当硅基颗粒的Dn50/Dv50值小于0.3时，硅基颗粒分布集中度较差，存在大量粒径过大或者过小的硅基颗粒。粒径过小的硅基颗粒过多会增大与电解液接触面积，产生更多的固体电解质界面膜(SEI膜)，消耗电池中有限的可逆锂。而硅基颗粒粒径过大不仅增加嵌锂膨胀过程中产生的应力，导致硅基颗粒破裂，裸露出新鲜界面与电解液反应，消耗可逆锂，恶化循环性能；同时粒径过大的硅基颗粒增加锂离子的扩散路径，增加浓差极化，影响电池的倍率性能。当硅基颗粒的Dn50/Dv50值大于0.85时，制备的产率低，成本高，难以大规模应用。
本发明所述的负极材料，其中优选的是，当所述石墨颗粒的平均球形度为C，所述硅基颗粒的平均球形度为D时，满足下述条件式(4)：
0.1≤D-C≤0.3        (4)。
本发明所述的负极材料，其中优选的是，所述硅基颗粒的平均球形度D≥0.8。
本发明所述的负极材料，其中优选的是，所述石墨颗粒的平均球形度C介于0.55到0.75之间，即0.55≤C≤0.75。
本发明所述的负极材料，其中优选的是，所述硅基颗粒的通式为：SiO xC yM z(I)，其中，0≤x≤2，0≤y≤1，0≤z≤0.5，M包括锂、镁、钛或铝中的至少一种。
本发明所述的负极材料，其中优选的是，所述硅基颗粒表面存在碳被膜、高分子被膜或二者的复合被膜。
本发明所述的负极材料，其中优选的是，所述石墨颗粒表面存在碳被膜、高分子被膜或二者的复合被膜。
本发明所述的负极材料，其中优选的是，所述碳被膜由定形碳、碳纳米管、碳纳米粒子、气相沉积碳纤维或石墨烯中的至少一种形成；进一步优选，所述碳被膜还含有金属，所述金属包括铝、钛中的至少一种。
本发明所述的负极材料，其中优选的是，所述高分子被膜由聚偏氟乙烯及其衍生物、羧甲基纤维素及其衍生物、聚乙烯基吡咯烷酮及其衍生物、聚丙烯酸及其衍生物或聚丁苯橡胶中的至少一种形成。其中，衍生物是指一种简单化合物中的氢原子或原子团被其他原子或原子团取代而衍生的较复杂的产物。
本发明所述的负极材料，其中优选的是，所述硅基颗粒的所述被膜的厚度为0.5-50nm。
本发明所述的负极材料，其中优选的是，所述硅基颗粒的所述被膜的质量占所述硅基颗粒总质量的0.1-10％。
本发明所述的负极材料，其中优选的是，所述硅基颗粒的粒径范围为0.01-50um。
本发明所述的负极材料，其中优选的是，在所述硅基颗粒的XRD衍射图中，当2θ归属于20.5°-21.5°最高强度的数值为I1，2θ归属于28.0°-29.0°最高强度的数值为I2时，满足I2/I1≤10，进一步优选I2/I1≤1。
本发明所述的负极材料，其中优选的是，所述硅基颗粒的比表面积为0.1-50m 2/g，进一步优选0.1-5m 2/g。
本发明所述的负极材料，其中优选的是，在所述石墨颗粒的拉曼散射峰中，当1330cm -1处的峰强度为I1330，1580cm -1处的峰强度为I1580时，满足 下述条件式(5)：
0.05≤I1330/I1580≤0.9        (5)。
本发明所述的负极材料，其中优选的是，所述石墨颗粒包括二次颗粒，所述二次颗粒占所述石墨颗粒总量的70wt％以上。
本发明所述的负极材料，其中优选的是，在所述石墨颗粒的XRD衍射峰中，当(004)峰和(110)峰峰强的比值为OI值时，满足下述条件式(6)：
1≤OI值≤30        (6)。
为此，本发明还提供一种负极极片，包括上述的负极材料。
为此，本发明还提供一种负极极片的制备方法，该方法包括以下步骤：
(a)将上述的负极材料和导电剂混合获得第一混合物；
(b)将所述第一混合物与粘结剂在溶剂中混合获得第一混合浆料；
(c)将所述第一混合浆料涂于集流体上，经过干燥、冷压、分条后得到该负极极片。
本发明所述的制备方法，其中优选的是，所述第一混合物中，硅基颗粒的含量为5-30wt％，导电剂的含量为0.5-5wt％，余量为石墨颗粒。
本发明所述的制备方法，其中优选的是，所述导电剂包括纳米导电炭黑、碳纳米管、碳纤维、鳞片石墨、石墨烯或科琴黑中的至少一种。
本发明所述的制备方法，其中优选的是，所述碳纳米管包括单壁碳纳米管、多壁碳纳米管或二者的组合；所述碳纤维包括气相生长碳纤维、纳米碳纤维或二者的组合。
本发明所述的制备方法，其中优选的是，所述第一混合物与所述粘结剂的重量比为100：1-6。
本发明所述的制备方法，其中优选的是，所述粘结剂包括聚丙烯酸、聚丙烯酸钠、聚丙烯酸钾、聚丙烯酸锂、聚酰亚胺、聚乙烯醇、羧甲基纤维 素、羧甲基纤维素钠、聚酰亚胺、聚酰胺酰亚胺、丁苯橡胶或聚偏氟乙烯中的至少一种。
本发明所述的制备方法，其中优选的是，所述溶剂包括去离子水或N-甲基吡咯烷酮中的至少一种。
本发明所述的制备方法，其中优选的是，所述集流体由铜、铜合金、镍或镍合金中的至少一种制得。
本发明所述的制备方法，其中优选的是，所述负极极片的活性层厚度为50-200μm，活性层单面压实密度为1.4～1.9g/cm 3，活性层孔隙率为15～35％。
为此本发明还提供一种锂离子二次电池，该电池包括：正极极片、上述的负极极片、隔离膜以及电解液。
为此本发明还提供一种锂离子二次电池的制备方法，该制备方法包括以下步骤：
S1、将正极材料、导电剂、粘结剂和溶剂混合搅拌后制得第一正极混合浆料；
S2、将步骤S1所得的第一正极混合浆料涂于集流体上，经过干燥、冷压、分条后获得正极极片；
S3、将步骤S2所得的正极极片、上述的负极极片与隔离膜通过卷绕，得到裸电池；
S4、将步骤S3所得的裸电池装入电池袋中，干燥后注入电解液并封装，经过化成后得到该锂离子二次电池。
本发明所述的制备方法，其中优选的是，所述正极材料包括锂复合氧化物，所述锂复合氧化物包括过渡金属，所述过渡金属包括镍、锰、钴或铁中的至少一种。
本发明所述的制备方法，其中优选的是，步骤S1中的所述导电剂包括纳米导电炭黑、碳纳米管、碳纤维、鳞片石墨、石墨烯或科琴黑中的至少一种。
本发明所述的制备方法，其中优选的是，所述隔离膜由玻璃纤维、聚酯、聚乙烯、聚丙烯或聚四氟乙烯中的至少一种制得；所述隔离膜为多孔聚合薄膜，其中，孔的直径为0.01微米-1微米；所述隔离膜的厚度为5微米-500微米。
本发明所述的制备方法，其中优选的是，所述电解液包括有机溶剂、锂盐和添加剂，所述锂盐为有机锂盐和/或无机锂盐。
本发明所述的制备方法，其中优选的是，所述有机溶剂包括碳酸乙烯酯、碳酸丙烯酯、碳酸二乙酯、碳酸甲乙酯、碳酸二甲酯、碳酸亚丙酯或丙酸乙酯中的至少一种。
本发明所述的制备方法，其中优选的是，所述有机锂盐包括六氟磷酸锂、四氟硼酸锂、二氟磷酸锂、双三氟甲烷磺酰亚胺锂、双(氟磺酰)亚胺锂、双草酸硼酸锂或二氟草酸硼酸锂中的至少一种。
为此本发明还提供一种电化学装置，该电化学装置包括：上述的负极极片。
为此本发明还提供一种电子装置，该电子装置包括：上述的锂离子二次电池和/或电化学装置。
本发明的有益效果如下：
第一，通过对负极材料中的硅基颗粒和石墨颗粒的形貌以及粒度分布的合理匹配，能均匀分散负极材料整体膨胀应力，使硅基颗粒填充在石墨颗粒 之间的缝隙中像齿轮一样相互嵌在一起，增加负极材料的压实密度，并抑制硅基颗粒膨胀产生的位移。
第二，在合理匹配硅基颗粒和石墨颗粒的形貌以及粒度分布的基础上，进一步限定：(1)负极材料中硅基颗粒的大小，将晶粒尺寸逐渐减小至非晶状态；(2)石墨颗粒的表面结构；(3)硅基颗粒和/或石墨颗粒表面存在被膜。最终得到循环性能、倍率性能显著改善的负极材料。并且，由该负极材料制备的负极极片，能够降低电池在循环过程中的变形率。
附图说明
图1为本发明实施例1的SiO颗粒和石墨颗粒的体积粒度分布图；
图2为本发明实施例1的SiO颗粒和石墨颗粒的颗粒数粒度分布图；
图3为本发明的实施例12中SiO的XRD图；
图4为本发明的实施例14中SiO的XRD图；
图5为本发明的实施例3和对比例1的变形性能对比图。
具体实施方式
以下对本发明的实施例作详细说明：本实施例在以本发明技术方案为前提下进行实施，给出了详细的实施方式和过程，但本发明的保护范围不限于下述的实施例，下列实施例中未注明具体条件的实验方法，通常按照常规条件。
本发明提供的负极材料，该负极材料包含硅基颗粒和石墨颗粒，当所述石墨颗粒的Dn50/Dv50值为A，所述硅基颗粒的Dn50/Dv50值为B时，满足下述条件式(1)至(3)：
0.1≤A≤0.65       (1)，
0.3≤B≤0.85       (2)，
并且，B>A          (3)，
其中，Dv50为颗粒在体积基准分布中累计体积分数达到50％时所对应的粒径；Dn50为颗粒在数量基准分布中累计数量分数达到50％时所对应的粒径。
其中，Dn50/Dv50值为通过激光散射粒度仪测试得到的Dn50与Dv50的比值，其数值越趋近于1，颗粒粒度分布越集中；包含硅基颗粒与石墨颗粒的复合负极材料中，当石墨颗粒的分布集中程度低于硅基颗粒的分布集中程度时，电池的循环性更好以及变形率更低，这是由于硅基材料的嵌锂膨胀远大于石墨材料，为了减小膨胀时产生的应力，硅基颗粒的平均粒径小于石墨颗粒的平均粒径，当极片上活性物质由硅基颗粒和石墨颗粒复合组成时，硅基颗粒较石墨颗粒分布更为集中有利于分散在石墨颗粒堆积的缝隙中，使其膨胀对极片的整体膨胀影响最小，改善其循环中与石墨颗粒的接触，从而改善电池的循环性能以及降低变形率。
具体的，当石墨颗粒的Dn50/Dv50值在0.1-0.65范围内时，电池的电性能最优；当石墨颗粒的Dn50/Dv50的值小于0.1时，石墨颗粒中存在细小颗粒和大颗粒过多；当细小颗粒过多导致材料比表面积过大，降低首次效率；当大颗粒过多时，增加了锂离子的传输距离，恶化了电池电池的变形率和倍率性能。并且，当石墨颗粒的Dn50/Dv50值大于0.65时，石墨颗粒的粒径分布过于集中，不利于其在负极极片中的堆积，且加工成本显著增加。
具体的，当硅基颗粒的Dn50/Dv50值在0.3-0.85范围内时，电池的电性能最优。当硅基颗粒的Dn50/Dv50值小于0.3时，硅基颗粒分布集中度较差，存在大量粒径过大或者过小的硅基颗粒。粒径过小的硅基颗粒过多会导致与电解液接触面积增大，产生更多的固体电解质界面膜(SEI膜)，消耗电解液以及电池中有限的可逆锂。而硅基颗粒粒径过大不仅增加嵌锂膨胀过程中产生的应力，从而导致硅基颗粒破裂，裸露出新鲜界面与电解液反应， 消耗可逆锂，恶化循环性能；同时粒径过大的硅基颗粒增加锂离子的扩散路径，增加浓差极化，影响电池的倍率性能。当硅基颗粒的Dn50/Dv50值大于0.85时，制备的产率低，成本高，难以大规模应用。
在一些实施例中，当所述石墨颗粒的平均球形度为C，所述硅基颗粒的平均球形度为D时，满足下述条件式(4)：
0.1≤D-C≤0.3        (4)。
在一些实施例中，所述硅基颗粒的平均球形度D≥0.8，例如但不限于0.8、0.9、1.0。
在一些实施例中，所述石墨颗粒的平均球形度C介于0.55到0.75之间，例如但不限于0.55、0.65、0.75。
在一些实施例中，所述硅基颗粒的通式为：SiO xC yM z(I)，其中，0≤x≤2，0≤y≤1，0≤z≤0.5，M包括锂、镁、钛或铝中的至少一种。例如但不限于商业硅氧化物SiO X(0.5<x<1.5)、SiOxCy(0.5<x<1.5，0＜y≤0.1)、SiOxCyLiz(0.5<x<1.5，0＜y≤0.1，0≤z≤0.1)。
在一些实施例中，所述硅基颗粒表面存在碳被膜、高分子被膜或二者的复合被膜。
在一些实施例中，所述石墨颗粒表面存在碳被膜、高分子被膜或二者的复合被膜。
在一些实施例中，所述碳被膜由定形碳、碳纳米管、碳纳米粒子、气相沉积碳纤维或石墨烯中的至少一种形成。
在一些实施例中，所述高分子被膜由聚偏氟乙烯及其衍生物、羧甲基纤维素及其衍生物、聚乙烯基吡咯烷酮及其衍生物、聚丙烯酸及其衍生物或聚丁苯橡胶中的至少一种形成。其中，衍生物是指一种简单化合物中的氢原子或原子团被其他原子或原子团取代而衍生的较复杂的产物。例如但不限于羧甲基纤维素钠、羧甲基纤维素锂、聚丙烯酸钠、聚丙烯酸铵。
在一些实施例中，所述硅基颗粒的所述被膜的厚度为0.5-50nm，例如但不限于0.5nm、10nm、20nm、30nm、40nm、50nm。
在一些实施例中，所述硅基颗粒的所述被膜的质量占所述硅基颗粒总质量的0.1-10％，例如但不限于0.1％、3％、5％、8％、10％。
在一些实施例中，所述硅基颗粒的粒径范围为0.01-50um，例如但不限于0.01um、1um、10um、20um、30um、40um、50um。
在一些实施例中，在所述硅基颗粒的XRD衍射图中，当2θ归属于20.5°-21.5°最高强度的数值为I1，2θ归属于28.0°-29.0°最高强度的数值为I2时，满足I2/I1≤10，例如但不限于10、5、2、1，其中进一步优选I2/I1≤1。
在一些实施例中，所述硅基颗粒的比表面积为0.1-50m 2/g，例如但不限于0.1m 2/g、5m 2/g、10m 2/g、20m 2/g、30m 2/g、40m 2/g、50m 2/g，进一步优选0.1-5m 2/g。
在一些实施例中，在所述石墨颗粒的拉曼散射峰中，当1330cm -1处的峰强度为I1330，1580cm -1处的峰强度为I1580时，满足下述条件式(5)：
0.05≤I1330/I1580≤0.9        (5)。
在一些实施例中，所述石墨颗粒包括二次颗粒，所述二次颗粒占所述石墨颗粒总量的70wt％以上。在另一些实施例中，所述石墨颗粒由70wt％以上的二次颗粒和余量的一次颗粒组成。
在一些实施例中，在所述石墨颗粒的XRD衍射峰中，当(004)峰和(110)峰峰强的比值为OI值时，满足下述条件式(6)：
1≤OI值≤30        (6)。
本发明提供的负极极片上涂覆有上述的负极材料。其中涂覆的方法按照常规电极材料涂覆方法即可，本发明对此不作限定。
本发明还提供上述负极极片的制备方法，包括以下步骤：
(a)、将上述的负极材料和导电剂混合获得第一混合物；
(b)、将所述第一混合物与粘结剂在溶剂中混合获得第一混合浆料；
(c)、将所述第一混合浆料涂于集流体上，经过干燥、冷压、分条后得到该负极极片。
在一些实施例中，所述第一混合物中，硅基颗粒的含量为5-30wt％，导电剂的含量为0.5-5wt％，余量为石墨颗粒。在一些实施例中，第一混合物包含5wt％硅基颗粒、0.5wt％导电剂，余量为石墨颗粒；在一些实施例中，第一混合物包含30wt％硅基颗粒、0.5wt％导电剂，余量为石墨颗粒；在一些实施例中，第一混合物包含30wt％硅基颗粒、5wt％导电剂，余量为石墨颗粒；在一些实施例中，第一混合物包含15wt％硅基颗粒、2.5wt％导电剂，余量为石墨颗粒。
在一些实施例中，所述导电剂包括纳米导电炭黑、碳纳米管、碳纤维、鳞片石墨、石墨烯或科琴黑中的至少一种。
在一些实施例中，所述碳纳米管包括单壁碳纳米管、多壁碳纳米管或二者的组合；所述碳纤维包括气相生长碳纤维、纳米碳纤维或二者的组合。
在一些实施例中，所述第一混合物与所述粘结剂的重量比为100：1-6，例如但不限于100：1、100：6、100：3。
在一些实施例中，所述粘结剂包括聚丙烯酸、聚丙烯酸钠、聚丙烯酸钾、聚丙烯酸锂、聚酰亚胺、聚乙烯醇、羧甲基纤维素、羧甲基纤维素钠、聚酰亚胺、聚酰胺酰亚胺、丁苯橡胶或聚偏氟乙烯中的至少一种。
在一些实施例中，所述溶剂包括去离子水、N-甲基吡咯烷酮中的至少一种。
在一些实施例中，所述集流体由铜、铜合金、镍或镍合金中的至少一种制得。
在一些实施例中，所述负极极片的活性层厚度为50-200μm，活性层单 面压实密度为1.4～1.9g/cm 3，活性层孔隙率为15～35％。
本发明提供的锂离子二次电池，该电池包括：正极极片、上述的负极极片、隔离膜以及电解液。
本发明还提供上述锂离子二次电池的制备方法，包括以下步骤：
S1、将正极材料、导电剂、粘结剂和溶剂混合搅拌后制得第一正极混合浆料；
S2、将步骤S1所得的第一正极混合浆料涂于集流体上，经过干燥、冷压、分条后获得正极极片；
S3、将步骤S2所得的正极极片、上述的负极极片与隔离膜通过卷绕，得到裸电池；
S4、将步骤S3所得的裸电池装入电池袋中，干燥后注入电解液并封装，经过化成后得到该锂离子二次电池。
在一些实施例中，所述正极材料包括锂复合氧化物，所述锂复合氧化物包括过渡金属，所述过渡金属包括镍、锰、钴或铁中的至少一种。
在一些实施例中，步骤S1中的所述导电剂包括纳米导电炭黑、碳纳米管、碳纤维、鳞片石墨、石墨烯或科琴黑中的至少一种。
在一些实施例中，所述隔离膜由玻璃纤维、聚酯、聚乙烯、聚丙烯或聚四氟乙烯中的至少一种制得；所述隔离膜为多孔聚合薄膜，其中，孔的直径为0.01微米-1微米；所述隔离膜的厚度为5微米-500微米。
在一些实施例中，所述电解液包括有机溶剂、锂盐和添加剂，所述锂盐为有机锂盐和/或无机锂盐。
在一些实施例中，所述有机溶剂包括碳酸乙烯酯、碳酸丙烯酯、碳酸二乙酯、碳酸甲乙酯、碳酸二甲酯、碳酸亚丙酯或丙酸乙酯中的至少一种。
在一些实施例中，所述有机锂盐包括六氟磷酸锂、四氟硼酸锂、二氟磷酸锂、双三氟甲烷磺酰亚胺锂、双(氟磺酰)亚胺锂、双草酸硼酸锂或二氟草酸硼酸锂中的至少一种。
本发明提供的电化学装置包括：上述的负极极片。
本发明提供的电子装置括：上述的锂离子二次电池和/或电化学装置。
一、粉末以及电池性能测试
1、粉末颗粒微观形貌观察：利用扫面电镜进行粉末微观形貌观察表征材料表面包覆情况，所选测试仪器为：OXFORD EDS(X-max-20mm 2)，加速电压为15KV，调整焦距，观测倍数从50K进行高倍观察，低倍下500-2000主要观察颗粒团聚情况。
2、球形度测试：利用马尔文自动图像粒度分析仪对一定数量(大于5000)分散的颗粒进行图像捕捉以及处理，然后通过图像导向拉曼光谱技术(MDRS)，准确分析颗粒的微观结构和形态，得到所有颗粒的最长直径以及最短直径，计算最短直径/最长直径的比值计算得到颗粒的球形度；
3、比表面积测试：在低温恒温下，测定不同相对压力时的气体在固体表面的吸附量，然后，基于布朗诺尔-埃特-泰勒吸附理论以及BET方程求得试样单分子层吸附量，从而计算出固体的比表面积。
测试时，称取1.5-3.5g粉末样品装入TriStar II 3020的测试测试样品管中，200℃脱气120min后进行测试。
4、粒度测试(颗粒的大小称为“粒径(Particle size)”，又称“粒度”或者“直径”)：50ml洁净烧杯中加入约0.02g粉末样品，加入约20ml去离子水，再滴加几滴1％的表面活性剂，使粉末完全分散于水中，120W超声清洗机中超声5分钟，利用MasterSizer 2000测试粒度分布，通过激光散射粒度仪测试得到的：颗粒在体积基准分布中累计体积分数达到50％时所 对应的直径，以及颗粒在数量基准分布中累计数量分数达到50％时所对应的直径。
5、碳含量测试：样品在富氧条件下由高频炉高温加热燃烧使碳、硫氧化成二氧化碳、二氧化硫，该气体经处理后进入相应的吸收池，对相应的红外辐射进行吸收再由探测器转化成对应的信号。此信号由计算机采样，经线性校正后转换成与二氧化碳、二氧化硫浓度成正比的数值，然后把整个分析过程的取值累加，分析结束后，此累加值在计算机中除以重量值，再乘以校正系数，扣除空白，即可获得样品中碳、硫百分含量。利用高频红外碳硫分析仪(上海徳凯HCS-140)进行样品测试。
6、金属元素测试：称取一定量的样品加入一定量的浓硝酸进行微波消解后得到溶液，并将所得到的溶液和滤渣进行多次洗涤并定容到一定的体积，通过ICP-OES测试其中的金属元素的等离子体强度，根据所测金属的标准曲线计算出溶液中金属含量，从而计算出材料中所含的金属元素的量。
7、XRD测试：称取样品1.0-2.0g倒入玻璃样品架的凹槽内，并用玻璃片将其压实和磨平，采用X射线衍射仪(布鲁克，D8)按照JJS K 0131-1996《X射线衍射分析法通则》进行测试，测试电压设置40kV，电流为30mA，扫描角度范围为10-85°，扫描步长为0.0167°，每个步长所设置的时间为0.24s。通过计算石墨的XRD衍射峰中(004)峰和(110)峰峰强的比值，得到石墨的OI值。
8、粉末材料扣式电池测试方法：将实施例中得到的负极材料、导电炭黑与粘结剂PAA按照质量比80：10：10加去离子水经过搅成浆料，利用刮刀涂层100um厚度的涂层，85℃经过12小时真空干燥箱烘干后，利用在干燥环境中用冲压机切成直径为1cm的圆片，在手套箱中以金属锂片作为对电极，隔离膜选择ceglard复合膜，加入电解液组装成扣式电池。用蓝电(LAND)系列电池测试测试对电池进行充放电测试，测试其充放电容量。
首先采用0.05C放电至0.005V，静止5分钟后，用50μA放电至0.005V，再静止5分钟后，用10μA放电至0.005V，得到材料的首次嵌锂容量；然后用0.1C充电至2V，得到首次脱锂容量。最终，用首次脱锂容量比上首次嵌锂容量即为材料的首次效率。
二、全电池评估
1、循环测试：测试温度为25和45℃，以0.7C恒流充电到4.4V，恒压充电到0.025C，静置5分钟后以0.5C放电到3.0V。以此步得到的容量为初始容量，进行0.7C充电/0.5C放电进行循环测试，以每一步的容量与初始容量做比值，得到容量衰减曲线。以25℃循环截至到容量保持率为90％的圈数记为电池的室温循环性能，以45℃循环截至到80％的圈数记为电池的高温循环性能，通过比较上述两种情况下的循环圈数而得到材料的循环性能。
2、放电倍率测试：在25℃下，以0.2C放电到3.0V，静置5min，以0.5C充电到4.45V，恒压充电到0.05C后静置5分钟，调整放电倍率，分别以0.2C、0.5C、1C、1.5C、2.0C进行放电测试，分别得到放电容量，以每个倍率下得到的容量与0.2C得到的容量对比，通过比较2C与0.2C下的比值比较倍率性能。
3、电池满充膨胀率测试：用螺旋千分尺测试半充(定义充电至3.7V至4.0V区间的全电池称为半充全电池，该过程称为半充)时新鲜电池的厚度，循环至400cls时，电池处于满充状态下，再用螺旋千分尺测试此时电池的厚度，与初始半充时新鲜电池的厚度对比，即可得此时满充电池膨胀率。
三、具体实施例与对比例
实施例1
1、负极材料的选取
(1)商业硅氧化物SiO颗粒(也写作SiO X，0.5<x<1.5，DV50＝5.3μm)，B＝Dn50/Dv50＝0.3，粒径范围0.01-20μm，平均球形度0.85，比表面积1.32m 2.g -1。
(2)石墨颗粒(由80wt％的二次颗粒和余量的一次颗粒组成)，DV50＝13.6，A＝Dn50/Dv50＝0.2，平均球形度为0.65；
上述SiO颗粒和石墨颗粒的体积粒度分布图参见图1，上述SiO颗粒和石墨颗粒的颗粒数粒度分布图参见图2。
2、负极极片的制备
该实施例的负极极片的制备方法包括以下步骤：
(a)将上述的负极材料SiO颗粒和石墨颗粒与导电剂纳米导电炭黑混合获得第一混合物，其中，SiO颗粒的含量为15wt％，导电剂的含量为 2.5wt％，余量为石墨颗粒；
(b)将第一混合物与粘结剂聚丙烯酸在溶剂去离子水中混合获得第一混合浆料，其中，第一混合物与与粘结剂的重量比为100：4；
(c)将第一混合浆料涂于集流体镍箔上，经过干燥、冷压、分条后得到该负极极片，其中，活性层厚度为150μm，活性层单面压实密度为1.7g/cm 3，活性层孔隙率为25％。
3、锂离子二次电池的制备
该实施例的锂离子二次电池的制备方法包括以下步骤：
(1)、将正极活性物质LiCoO 2、纳米导电炭黑、粘结剂聚偏二氟乙烯(PVDF)按重量比96.7：1.7：1.6在N-甲基吡咯烷酮溶剂体系中充分搅拌混合均匀后，涂覆于Al箔上，经烘干、冷压、分条，得到正极极片。
(2)、将步骤(1)所得的正极极片、上述的负极极片与隔离膜聚乙烯(PE)多孔聚合薄膜(孔的直径为0.01微米-1微米；隔离膜的厚度为200微米)通过卷绕，得到裸电池；
(3)电解液的制备：在干燥氩气环境下，在碳酸丙烯酯(PC)，碳酸乙烯酯(EC)，碳酸二乙酯(DEC)以重量比1:1:1混合而成的溶剂溶液中，加入六氟磷酸锂(LiPF 6)混合均匀，其中LiPF 6的浓度约为1.15mol/L，再加入12wt％的氟代碳酸乙烯酯(FEC)后混合均匀得到电解液。
(4)、将步骤(2)所得的裸电池装入电池袋铝塑膜中，干燥后注入步骤(3)所得的电解液并封装，经过化成后得到该锂离子二次电池，即全电池。
该实施例所选负极材料以及所得全电池的性能评价结果见表1(其中的克容量为脱锂截至电压为2.0V所获得的容量，下同)和表1-1。
实施例2-3
与实施例1不同之处见表1。该实施例所选负极材料以及所得全电池的性能评价结果见表1和表1-1。
对比例1
与实施例1不同之处见表1。该实施例所选负极材料以及所得全电池的性能评价结果见表1和表1-1。
表1
Figure PCTCN2020081370-appb-000001
Figure PCTCN2020081370-appb-000002
表1-1
Figure PCTCN2020081370-appb-000003
由表1和表1-1可知，实施例1-3满足：石墨颗粒的Dn50/Dv50值在0.1-0.65范围内，硅基颗粒的Dn50/Dv50值在0.3-0.85范围内，且硅基颗粒的Dn50/Dv50值大于石墨颗粒的Dn50/Dv50值，最终得到的全电池性能优异。然而，不满足上述条件的对比例1得到的全电池性能明显劣于实施例。具体的，实施例3和对比例1的变形性能对比图参见图5。
实施例4-6
与实施例1不同之处见表2。该实施例所选负极材料以及所得全电池的性能评价结果见表2和表2-1。
对比例2-3
与实施例4不同之处见表2。该实施例所选负极材料以及所得全电池的性能评价结果见表2和表2-1。
表2
Figure PCTCN2020081370-appb-000004
Figure PCTCN2020081370-appb-000005
表2-1
Figure PCTCN2020081370-appb-000006
由表2和表2-1可知，实施例4-6满足：石墨颗粒的Dn50/Dv50值在0.1-0.65范围内，硅基颗粒的Dn50/Dv50值在0.3-0.85范围内，且硅基颗粒的Dn50/Dv50值大于石墨颗粒的Dn50/Dv50值，最终得到的全电池性能优异。然而，不满足上述条件的对比例2-3得到的全电池性能明显劣于实施例。
Dn50/Dv50表征颗粒分布的集中程度，其数值越趋近于1，颗粒粒度分布越集中。由表2和表2-1，从实施例4-6和对比例2-3的电池性能评价结果可以看出，当SiO颗粒的Dn50/Dv50值小于石墨颗粒的Dn50/Dv50值， 电池性能较好。这是由于硅基材料的嵌锂膨胀远大于石墨材料，为了减小膨胀时产生的应力，硅基颗粒的平均粒径小于石墨颗粒，当极片上活性物质由硅基颗粒和石墨颗粒复合组成时，硅基颗粒较石墨颗粒分布更为集中有利于分散在石墨颗粒堆积的缝隙中，使其膨胀对极片的整体膨胀影响最小。此外，SiO颗粒的Dn50/Dv50值越大，匹配同样的石墨可以改善电池循环、变形性能，这是由于硅基颗粒分布集中度差时，存在大量过大或者过小的颗粒，颗粒过多会导致与电解液接触面积增大，产生更多的SEI层，消耗电解液以及电池中有限的可逆锂。且颗粒过大不仅增加嵌锂膨胀过程中产生的应力，导致颗粒破裂，裸露出新鲜界面与电解液反应，消耗可逆锂，恶化循环性能；同时大的颗粒增加锂离子的扩散路径，增加浓差极化，影响电池的倍率性能。
另外，由表2和表2-1可知，当石墨颗粒的Dn50/Dv50值小于0.1时如对比例3，石墨颗粒中存在细小颗粒和大颗粒过多。当细小颗粒过多导致材料比表面积过大，降低首次效率；当大颗粒过多时，增加锂离子的传输距离，恶化电池的倍率性能和变形率。当石墨颗粒的Dn50/Dv50的值大于0.65时如对比例2，石墨颗粒的粒径分布过于集中，不利于其在负极极片中的堆积，导致电池的变形加剧，电接触恶化，循环也随之恶化，且加工成本显著增加。
实施例7-9
与实施例1不同之处见表3。该实施例所选负极材料以及所得全电池的性能评价结果见表3和表3-1，其中I1330、I1580是指对应的石墨颗粒或SiO颗粒的拉曼散射峰中1330cm -1、1580cm -1处的峰强度。
对比例4
与实施例7不同之处见表3。该实施例所选负极材料以及所得全电池的性能评价结果见表3和表3-1。
表3
Figure PCTCN2020081370-appb-000007
表3-1
Figure PCTCN2020081370-appb-000008
由表3和表3-1，通过实施例7-9和对比例4的对比可以看出，随着SiO颗粒的平均球形度减小，电池的容量保持率下降，变形率提高。这是由于SiO颗粒在嵌锂的过程中会产生巨大的体积膨胀，膨胀产生的应力使颗粒表面破裂，暴露出新鲜界面与电解液接触，产生更多的SEI层，并加速电 解液对SiO颗粒的腐蚀。球形度较高的SiO颗粒能有效均匀分散嵌锂膨胀所产生的应力，缓解表面裂纹产生，减少表面SEI层堆积以及被腐蚀的速率。
实施例10-11
与实施例7不同之处见表4，其中I1330、I1580是指对应的石墨颗粒或SiO颗粒的拉曼散射峰中1330cm -1、1580cm -1处的峰强度。该实施例所选负极材料以及所得全电池的性能评价结果见表4和表4-1。
对比例4
与实施例7不同之处见表4。该实施例所选负极材料以及所得全电池的性能评价结果见表4和表4-1。
表4
Figure PCTCN2020081370-appb-000009
表4-1
Figure PCTCN2020081370-appb-000010
Figure PCTCN2020081370-appb-000011
由表4和表4-1，从实施例7、10-11和对比例5、6的电池性能评价结果可以看出，石墨颗粒的平均球形度过大或者过小都会影响电池的电化学性能。石墨颗粒平均球形度过大无法将硅基颗粒卡在石墨颗粒的间隙中，增大SiOx颗粒在膨胀收缩的过程中造成的颗粒位移，从而增大电池变形，引起容量衰减；石墨球形度过小使各项异性增加，减缓锂离子的嵌入速度，影响电池的动力学。
实施例12-14
与实施例7不同之处见表5，其中I1是对应的SiO颗粒从XRD衍射图中2θ归属于20.5°-21.5°的最高强度数值，I2是对应的SiO颗粒从XRD衍射图中与归属于28.0°-29.0°的最高强度数值。该实施例所选负极材料以及所得全电池的性能评价结果见表5和表5-1。且实施例12和14中SiO颗粒的XRD图参见图3和4。
对比例7
与实施例7不同之处见表5。该实施例所选负极材料以及所得全电池的性能评价结果见表5和表5-1。
表5
Figure PCTCN2020081370-appb-000012
表5-1
Figure PCTCN2020081370-appb-000013
由表5和表5-1，从实施例7、12、13、14和对比例7随着I2/I1的值不断增加，循环性能不断降低，膨胀增加，其倍率性能变差。I 2/I 1的值反映了SiO颗粒受到歧化的影响程度，其值越大，表明SiO颗粒内部由于歧化产生 的纳米硅晶粒的尺寸越大，在嵌锂过程中会导致局部区域的应力急剧增大，从而导致材料循环过程中负极极片结构破坏，另外由于产生纳米晶分布，其在离子扩散过程中影响晶界扩散的能力。
实施例15-17
与实施例7不同之处见表6，其中D是指石墨颗粒的拉曼散射峰1330cm -1处的峰强度，G是指石墨颗粒的拉曼散射峰1580cm -1处的峰强度。该实施例所选负极材料以及所得全电池的性能评价结果见表6和表6-1。
对比例8-9
与实施例15不同之处见表6。该实施例所选负极材料以及所得全电池的性能评价结果见表6和表6-1。
表6
Figure PCTCN2020081370-appb-000014
表6-1
Figure PCTCN2020081370-appb-000015
Figure PCTCN2020081370-appb-000016
由表6和表6-1，从实施例15-17和对比例8-9的电池性能评价结果可以看出，当石墨颗粒的拉曼散射峰的强度比D/G过低时，其表面有序度高，与电解液的浸润性差，恶化电池动力学性能；当石墨颗粒的拉曼散射峰的强度比D/G过大时，其表面存在的被膜过厚、且含有大量缺陷的无定形碳被膜，导致该材料的首次效率和克容量降低；此外过厚的无定形碳会消耗部分锂离子，导致容量衰减加速。
实施例18
与实施例1不同之处在于，SiO颗粒的表面存在被膜，被膜中金属元素种类、金属元素含量和碳含量表征见表7(其中“-”表示未添加该物质)。且被膜的厚度为10nm，被膜的质量是SiO颗粒总质量的0.425％。
该实施例所选负极材料以及所得全电池的性能评价结果见表7和表7-1。
实施例19-21
与实施例18不同之处见表7，。该实施例所选负极材料以及所得全电池的性能评价结果见表7和表7-1。
表7
Figure PCTCN2020081370-appb-000017
表7-1
Figure PCTCN2020081370-appb-000018
由表7和表7-1，从实施例1与实施例18-21的测试结果可以看出，在同样满足粒径匹配关系的情况下，当SiO颗粒表面存在被膜后可以进一步提高锂离子电池的循环性能和/或倍率性能和抗变形能力，并且由铝和碳形成的碳被膜可以更好地提高锂离子电池的循环性能和/或倍率性能和抗变形能力。
当然，本发明还可有其它多种实施例，在不背离本发明精神及其实质的情况下，熟悉本领域的技术人员可根据本发明作出各种相应的改变和变形，但这些相应的改变和变形都应属于本发明的保护范围。

Claims (10)

  1. 一种负极材料，其特征在于，所述负极材料包含硅基颗粒和石墨颗粒，当所述石墨颗粒的Dn50/Dv50值为A，所述硅基颗粒的Dn50/Dv50值为B时，满足下述条件式(1)至(3)：
    0.1≤A≤0.65        (1)，
    0.3≤B≤0.85        (2)，
    并且，B>A           (3)，
    其中，Dv50为颗粒在体积基准分布中累计体积分数达到50％时所对应的粒径；Dn50为颗粒在数量基准分布中累计数量分数达到50％时所对应的粒径。
  2. 根据权利要求1所述的负极材料，其特征在于，当所述石墨颗粒的平均球形度为C，所述硅基颗粒的平均球形度为D时，满足下述条件式(4)：
    0.1≤D-C≤0.3        (4)。
  3. 根据权利要求1所述的负极材料，其特征在于，所述硅基颗粒的平均球形度D≥0.8。
  4. 根据权利要求1所述的负极材料，其特征在于，所述石墨颗粒的平均球形度C介于0.55到0.75之间。
  5. 根据权利要求1所述的负极材料，其特征在于，所述硅基颗粒的通式为：SiO xC yM z(I)，其中，0≤x≤2，0≤y≤1，0≤z≤0.5，M包括锂、镁、钛或铝中的至少一种；
    所述硅基颗粒表面存在碳被膜、高分子被膜或二者的复合被膜，所述被膜的厚度为0.5-50nm，所述被膜的质量占所述硅基颗粒总质量的0.1-10％；
    所述硅基颗粒的粒径范围为0.01-50um，所述硅基颗粒的比表面积为0.1-50m 2/g，进一步优选0.1-5m 2/g；
    在所述硅基颗粒的XRD衍射图中，当2θ归属于20.5°-21.5°最高强度的数值为I1，2θ归属于28.0°-29.0°最高强度的数值为I2时，满足I2/I1≤10，进一步优选I2/I1≤1。
  6. 根据权利要求1所述的负极材料，其特征在于，所述石墨颗粒包括二次颗粒，所述二次颗粒占所述石墨颗粒总量的70wt％以上；
    所述石墨颗粒表面存在碳被膜、高分子被膜或二者的复合被膜；
    在所述石墨颗粒的拉曼散射峰中，当1330cm -1处的峰强度为I1330，1580cm -1处的峰强度为I1580时，满足下述条件式(5)：
    0.05≤I1330/I1580≤0.9        (5)；
    在所述石墨颗粒的XRD衍射峰中，当(004)峰和(110)峰峰强的比值为OI值时，满足下述条件式(6)：
    1≤OI值≤30        (6)。
  7. 根据权利要求5或6所述的负极材料，其特征在于，所述碳被膜包括无定形碳、碳纳米管、碳纳米粒子、气相沉积碳纤维或石墨烯中的至少一种；所述高分子被膜由聚偏氟乙烯及其衍生物、羧甲基纤维素及其衍生物、聚乙烯基吡咯烷酮及其衍生物、聚丙烯酸及其衍生物或聚丁苯橡胶中的至少一种形成。
  8. 一种负极极片，其特征在于，包括权利要求1-7任一项所述的负极材料。
  9. 一种电化学装置，其特征在于，包括：权利要求8所述的负极极片。
  10. 一种电子装置，其特征在于，包括：权利要求9所述的电化学装 置。
PCT/CN2020/081370 2020-03-26 2020-03-26 负极材料、负极极片、包含该负极极片的电化学装置及电子装置 WO2021189349A1 (zh)

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