Patent Application
20230343943
This application pertains to the field of battery technologies, in particular, relates to the field of lithium-ion battery technologies, and specifically, to two negative electrode materials, a negative electrode plate coated with such negative electrode material, and an electrochemical apparatus and electronic apparatus containing such negative electrode plate.
An important aspect of technological innovation in batteries, and in particular in lithium-ion batteries, is to continuously improve the energy density. At present, the actual capacity of mainstream graphite materials is close to the theoretical capacity (372 mAh/g), and there is already a bottleneck in improving the energy density. Silicon-based negative electrode materials have attracted much attention and research because of their advantages such as abundant reserves, ultra-high theoretical capacity (4200 mAh/g), and environmental friendliness. However, the volume swelling (more than 300%) of the silicon-based negative electrode materials during cycling has seriously affected the process of industrial application of the silicon-based negative electrode materials.
Main methods to solve problems such as rapid attenuation of cycling (capacity retention rate after 400 cycles is lower than 80%) due to large volume swelling (120%-300%) and poor electrical conductivity (≤1 S/m) of silicon materials during cycling are as follows. (1) Nanosize silicon materials. The volume change of nano-silicon materials during cycling is small (<300%). Compared with non-nano materials (particle size >1 μm), nano materials are not easily broken and pulverized after swelling, which is conducive to maintaining the structural stability of the materials. (2) Perform surface coating and modification for silicon negative electrode materials, especially carbon coating. This can increase the conductivity of materials (the conductivity of materials after carbon coating is greater than 100 S/m) and alleviate the swelling (<80%). (3) Mix silicon-containing materials with graphite or other materials (metals or non-metals). Excellent electrical conductivity and extensibility of graphite and other materials can significantly alleviate the volume swelling of silicon materials during cycling and increase the electrical conductivity of the system. (4) Optimize a binder for a silicon negative electrode, to enhance adhesion of the silicon-containing negative electrode and restrain the swelling of silicon materials.
However, the above methods have the following defects and problems: Nano materials of a large specific surface area (materials with particle size less than 100 nm can have a specific surface area as high as 100 m2/g) consume more electrolyte to form SEI films, resulting in a low initial coulombic efficiency. Moreover, the nano materials feature difficult preparation and high price, and these series of characteristics limit further application of the nano silicon materials. Existing CVD alkyne gas coating and solid-phase pitch coating cannot improve the electrical conductivity significantly, and the problem of electrical contact failure caused by swelling during cycling cannot be solved. Simple mechanical mixing of the silicon-based negative electrode with graphite of good electrical conductivity cannot guarantee the uniformity of mixing, and to ensure the contact between graphite and silicon-based particles during the cycling, a binder with high adhesion is required, and this will result in a decrease in rate performance.
In view of the foregoing problems in the prior art, one of the objectives of this application is to provide two types of silicon-containing negative electrode materials with better electrical conductivity and more suitable for electrochemical apparatuses, especially for lithium-ion batteries. In this application, composition and outer surface layer of silicon-containing negative electrode materials are taken into account, and two types of silicon-containing negative electrode materials with long cycle life and low swelling rate are obtained.
Another objective of this application is to further provide a negative electrode plate including the foregoing negative electrode materials, and an electrochemical apparatus and electronic apparatus containing such negative electrode plate.
In view of this, this application provides a negative electrode material including a silicon compound SiOx, a first conductive layer, and a second conductive layer; where 0.5≤x≤1.5; at least part of the first conductive layer is present between the silicon compound and the second conductive layer; and the first conductive layer includes graphene, and the second conductive layer includes carbon nanotubes.
In view of this, this application further provides a negative electrode material including a silicon compound SiOx, a first conductive layer, and a second conductive layer; where 0.5≤x≤1.5; at least part of the first conductive layer is present between the silicon compound and the second conductive layer; and the first conductive layer includes carbon nanotubes, and the second conductive layer includes graphene.
For the negative electrode material described in this application, preferably, the first conductive layer substantially coats the silicon compound, and the second conductive layer substantially coats the first conductive layer.
For the negative electrode material described in this application, preferably, a median particle size A μm of the silicon compound and an average tube length B μm of the carbon nanotubes satisfy the following relational expression: 0.5*A≤B≤2*π*A. In this application, * means multiplication.
For the negative electrode material described in this application, preferably, a median particle size C μm of the negative electrode material and a median particle size A μm of the silicon compound satisfy the following relational expression: A≤C≤2A.
For the negative electrode material described in this application, preferably, the median particle size A μm of the silicon compound and an average flake diameter D μm of the graphene satisfy the following relational expression: 0.7*π*A2≤n*D2≤1.5*π*A2, where n is the number of graphene flakes on surface of a single silicon compound particle, and 2≤n≤20.
For the negative electrode material described in this application, preferably, the negative electrode material further includes an oxide MeOy layer, the oxide MeOy layer having at least one of the following characteristics:
For the negative electrode material described in this application, preferably, the negative electrode material further includes a polymer layer, the polymer layer having at least one of the following characteristics:
For the negative electrode material described in this application, preferably, the negative electrode material has at least one of the following characteristics:
In view of this, this application further provides a negative electrode material including the foregoing negative electrode material and further including a carbon material, a binder, a conductive material, or any combination thereof. The negative electrode material has at least one of the following characteristics:
In view of this, this application further provides a negative electrode plate including a current collector and the foregoing negative electrode material, where the negative electrode material is applied onto at least one surface of the current collector.
For the negative electrode material described in this application, preferably, the negative electrode plate has a thickness of 50 μm to 200 μm, a single-surface compacted density of 1.2 g/cm3 to 2.0 g/cm3, and a resistance of 0.001Ω to 1000Ω.
For the negative electrode plate described in this application, preferably, peeling strength between the negative electrode material and the current collector is greater than 10 N/m.
In view of this, this application further provides an electrochemical apparatus including a positive electrode plate, the foregoing negative electrode plate, a separator, and an electrolyte.
In view of this, this application further provides an electronic apparatus including the foregoing electrochemical apparatus.
Beneficial effects of this application are as follows: In the negative electrode material of this application, the silicon compound is stepwise coated with graphene and carbon nanotubes. This combines respective advantages of a two-dimensional long-range flake graphene conductive material and a one-dimensional long-range carbon nanotube conductive material, and is more conducive to improving cycling performance of a battery. In particular, the silicon compound is coated first with graphene and then with carbon nanotubes to form a layered structure, more conducive to suppressing swelling of silicon in the negative electrode plate during cycling of the battery, thus further reducing a full charge swelling rate of the battery. Moreover, the preparation method of the foregoing negative electrode material is simple and easy to use and can realize low-cost industrial preparation.
The following describes some embodiments of this application in detail. These embodiments are implemented based on technical solutions of this application, and detailed implementations and processes are given. However, the protection scope of this application is not limited to the following embodiments, and experimental methods with no specific conditions specified in the following embodiments are usually performed in accordance with general conditions.
In some embodiments, preferably, during preparation of negative electrode plate, a Cu foil is coated with a negative electrode material with a coating thickness of 50 μm to 200 μm and a single-surface compacted density of 1.2 g/cm3 to 2.0 g/cm3. When the coating thickness and the single-surface compacted density fall within the foregoing ranges, resistance of the negative electrode plate falls within a range of 0.001Ω to 1000Ω.
In some embodiments, preferably, the negative electrode material includes an oxide MeOy layer, at least part of the oxide MeOy layer being present between a silicon compound and a first conductive layer. Further preferably, Me in the oxide MeOy layer includes at least one of Al, Si, Ti, Mn, V, Cr, Co, or Zr, where 0.5≤y≤3, and the oxide MeOy layer includes a carbon material.
In some embodiments, preferably, thickness of the oxide MeOy layer is 0.5 nm to 100 nm.
In some embodiments, preferably, a process for preparing an AlOy layer of the negative electrode material is as follows.
(1) SiOx powder, a porogenic agent, and an oxide precursor AlXn form a mixed solution with the presence of an organic solvent and deionized water;
(2) The silicon compound SiOx particles containing the oxide AlOy layer, an organic solvent, and a carbon precursor are mixed to form a mixed solution;
The carbon precursor is a mixture of phenolic resin and hexamethylenetetramine, where
A weight ratio of the SiOx particles to the carbon precursor is 5-20.
The organic solvent includes at least one of the following solvents: ethanol, methanol, n-hexane, N,N-dimethylformamide, pyrrolidone, acetone, toluene, isopropanol, or n-propyl alcohol; and a volume of the organic solvent is twice (mL/g) to 5 times (mL/g) a weight of the SiOx particles.
The porogenic agent includes at least one of the following compounds: polyvinylpyrrolidone, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, hexadecyl trimethyl ammonium bromide, or octadecyl trimethyl ammonium bromide.
A mass ratio of the SiOx powder, the porogenic agent, the oxide precursor AlXn, and deionized water is 100:1-4:0.5-10:1.5-30.
1. Particle Size Test
0.02 g of sample powder was added into a 50 mL clean beaker, and 20 mL of deionized water was added into the breaker, with a few drops of surfactant (1%) added to make the powder completely dispersed in the water. Then, the powder was subjected to ultrasound for 5 minutes in a 120 W ultrasonic cleaning machine, and particle size distribution was tested with a MasterSizer 2000.
2. SEM Test
Scanning electron microscope characterization was recorded with a PhilipsXL-30 field emission scanning electron microscope. Testing was performed under the conditions of 10 kV and 10 mA.
3. Test for Length of Carbon Nanotubes
0.01 g of carbon nanotubes and 1 g of sodium dodecylbenzene sulfonate were taken and added to 100 g of deionized water for ultrasonic dispersion, and then 0.2 g of a resulting solution was taken and applied onto copper foil. A scanning electron microscope was used to observe and measure lengths of 100 carbon nanotubes, and an average value thereof was taken as an average tube length of carbon nanotubes.
4. Test for Average Flake Diameter of Graphene
0.01 g of graphene and 1 g of sodium dodecylbenzene sulfonate were taken and added to 100 g of deionized water for ultrasonic dispersion, and then 0.2 g of a resulting solution was taken and applied onto copper foil. A scanning electron microscope was used to observe and measure flake diameters of 100 graphene flakes, and an average value thereof was taken as an average flake diameter of graphene.
5. Test for Number of Layers of Graphene
An atomic force microscope was used to test graphene. Thickness of a single layer graphene is generally 0.4 nm-0.7 nm. The number of layers of graphene could be directly calculated using an AFM height curve.
6. Test for Number n of Graphene Flakes on Surface of Single Silicon Compound Particle
Under a field of view of a scanning electron microscope, a single silicon compound particle with graphene present on surface was magnified to a suitable magnification (10000×-50000×) with the one and only intact silicon compound particle under the field of view. The number of graphene flakes present on the surface of the silicon compound particle under the field of view was counted, such counting was performed on 100 silicon compound particles, and the number of graphene flakes was recorded as N. The number n of graphene flakes on surface of a single silicon compound particle was N/100*2, that was, N/50.
7. Conductivity Test
A resistivity tester (Suzhou Jingge Electronics ST-2255A) was used. 5 g of powder sample was taken and pressed at a constant pressure of 5000 kg±2 kg for 15s-25s with an electronic pressing machine. The sample was then placed between the electrodes of the tester with a sample height of h (cm), a voltage of U, a current of I, and a resistance of R (KΩ). The area of the powder-pressed sheet was S=3.14 cm2, and the electronic conductivity of the powder sample was calculated according to the formula 6=h/(S*R)/1000 in S/m.
8. High-Temperature Cycling Test
At a test temperature of 45° C., a battery was charged to 4.4 V at a constant current of 0.7 C, constant-voltage charged to 0.025 C, left standing for 5 minutes, and then discharged to 3.0 V at 0.5 C. A capacity obtained in this cycle was an initial capacity. Then, a 0.7 C charge and 0.5 C discharge cycling test was performed. A ratio of the capacity of each cycle to the initial capacity was calculated to obtain a capacity degradation curve.
9. Test for Full-Charge Swelling Rate of Battery
Thickness of a fresh battery at half charge was measured by a spiral micrometer. After 400 cycles, the battery was fully charged, the thickness of the battery was measured again by the spiral micrometer, and compared with the initial thickness of the fresh battery at half charge to obtain a swelling rate of the fully-charged battery at that time.
10. Discharge Rate Test
At 25° C., a battery was discharged to 3.0 V at 0.2 C, left standing for 5 minutes, charged to 4.4 V at 0.5 C, constant-voltage charged to 0.05 C, and left standing for 5 minutes. The discharge rate was adjusted and discharge tests were conducted separately at 0.2 C, 0.5 C, 1 C, 1.5 C, and 2.0 C respectively to obtain discharge capacities. The capacity obtained at each rate was compared with the capacity obtained at 0.2 C to obtain a ratio. Rate performance of the battery was compared by comparing the ratios.
(I) Preparation of Negative Electrode Material
1. Commercial silicon oxide SiOx (0.5<x<1.5, and Dv50=5 μm), conductive material 1, polymer 1, and solvent deionized water were added into an MSK-SFM-10 vacuum stirrer in a specified ratio and stirred for 180 minutes to form a slurry. The stirrer had a revolution speed of 10 r/min-40 r/min and a rotation speed of 1000 r/min-1500 r/min.
2. The slurry obtained in step 1 was transferred to a spray drying granulator, and the slurry formed tiny fogdrops at a centrifugal atomizer of the spray drying granulator. A rotation speed of the centrifugal disk was 500 r/min-5000 r/min. Then, the tiny fogdrops were dried and cooled in the spray drying granulator to obtain powder. The spray drying granulator had an inlet temperature of 260° C. and an outlet temperature of 105° C.
3. The powder obtained in step 2, conductive material 2, polymer 2, and solvent deionized water were added into the MSK-SFM-10 vacuum stirrer in a specified ratio and stirred for 180 minutes to form a slurry. The stirrer had a revolution speed of 10 r/min-40 r/min and a rotation speed of 1000 r/min-1500 r/min.
4. The slurry obtained in step 3 was transferred to the spray drying granulator, and the slurry formed tiny fogdrops at the centrifugal atomizer of the spray drying granulator. A rotation speed of the centrifugal disk was 500 r/min-5000 r/min. Then, the tiny fogdrops were dried and cooled in the spray drying granulator to obtain powder (which was a negative electrode material). The spray drying granulator had an inlet temperature of 260° C. and an outlet temperature of 105° C.
In the foregoing steps, for composition and amount of the commercial silicon oxide SiOx, conductive material 1, and conductive material 2, refer to Table 1.
For particle size and conductivity of the negative electrode material, refer to Table 1-1.
(II) Preparation of Negative Electrode Plate
The negative electrode material obtained in step (I), a conductive agent acetylene black, and polyacrylic acid (PAA) were fully stirred and mixed to uniformity at a weight ratio of 95:1.2:3.8 in deionized water, and a resulting mixture was applied onto two surfaces of a Cu foil, followed by drying, cold pressing, and slitting to obtain a negative electrode plate.
The negative electrode material was applied onto the Cu foil with a coating thickness of 100 μm and a single-surface compacted density of 1.76 g/cm3 to 2.0 g/cm3.
(III) Preparation of Electrolyte
Under a dry argon environment, propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) were mixed at a weight ratio of 1:1:1 to obtain a solvent solution, and lithium hexafluorophosphate (LiPF6) were added and well mixed, where the concentration of LiPF6 was 1.15 mol/L. Then, 12 wt % fluoroethylene carbonate (FEC) was added and well mixed to obtain an electrolyte.
(IV) Preparation of Lithium-Ion Battery
An active substance LiCoO2, conductive carbon black, and a binder polyvinylidene fluoride (PVDF) were fully stirred and mixed to uniformity in an N-methylpyrrolidone solvent system at a weight ratio of 96.7:1.7:1.6, and then a resulting mixture was applied onto an Al foil, followed by drying and cold pressing to obtain a positive electrode plate. A PE porous polymer film was used as a separator. The positive electrode plate, the separator, and the negative electrode plate prepared in step (II) were stacked in sequence, so that the separator was sandwiched between the positive and negative electrode plates for separation, and winding was performed to obtain an electrode assembly. The electrode assembly was placed in an outer package, the electrolyte prepared in step (III) was injected, and packaging was performed, followed by processes such as formation, degassing, and trimming, to obtain a full battery.
For cycling performance and discharge rate of the obtained battery, refer to Table 1-2.
For a difference from Example 1-1, refer to Table 1. For composition and amount of the commercial silicon oxide SiOx, conductive material 1, and conductive material 2, refer to Table 1. For particle size and conductivity of the negative electrode material, refer to Table 1-1. For cycling performance and discharge rate of the obtained battery, refer to Table 1-2.
For a difference from Example 1-1, refer to Table 1. For composition and amount of the commercial silicon oxide SiOx, conductive material 1, and conductive material 2, refer to Table 1. For particle size and conductivity of the negative electrode material, refer to Table 1-1. For cycling performance and discharge rate of the obtained battery, refer to Table 1-2.
It can be learned from Table 1-1 that the silicon oxide particles coated with the conductive material have increased particle size, and the commercial silicon oxide in Example 1-1 to Example 1-3 is coated with two types of conductive materials. Therefore, the resulting electrode material has significantly improved conductivity as compared with Comparative example 1 and Comparative example 2 in which the commercial silicon oxide is coated with only one type of conductive material.
Refer to Table 1-2. The comparisons between Examples 1-1 to 1-3 and Comparative examples 1 and 2 illustrate that the composite coating of graphene and carbon nanotubes on the silicon oxide particles is more conducive to improving the cycling performance of the battery; moreover, the silicon oxide particles are coated first with graphene and then with carbon nanotubes to form a layered structure, which is more conducive to suppressing swelling of silicon-containing particles in the negative electrode plate during cycling of the battery, thus further reducing a full charge swelling rate of the battery.
For a difference from Example 1-1, refer to Table 2. For composition and amount of the commercial silicon oxide SiOx, conductive material 1, conductive material 2, polymer 1, and polymer 2, refer to Table 2. For particle size and conductivity of the negative electrode material, refer to Table 2-1. For cycling performance and discharge rate of the obtained battery, refer to Table 2-2.
For a difference from Example 1-1, refer to Table 2. For composition and amount of the commercial silicon oxide SiOx, conductive material 1, conductive material 2, polymer 1, and polymer 2, refer to Table 2. For particle size and conductivity of the negative electrode material, refer to Table 2-1. For cycling performance and discharge rate of the obtained battery, refer to Table 2-2.
It can be learned from Table 2-1 that increased amount of the conductive material applied on the silicon oxide particles causes agglomeration of particles, leading to increased particle size WO of the negative electrode material; and the conductivity of the negative electrode material increases with the increasing of the coating amount of the conductive material. However, the increase rate of the conductivity of the negative electrode material decreases when the coating amount of the conductive material increases to a specified value.
Refer to Table 2-2. The comparisons between Example 1-1, Examples 2-1 to 2-4, and Comparative examples 3 to 6 illustrate that increasing of the coating amount of graphene in the negative electrode material is conducive to improving the cycling performance and rate performance of the battery while suppressing swelling of the silicon-containing particles in the negative electrode plate and reducing the full charge swelling rate of the battery, however, excessive coating amount of graphene in the negative electrode material, especially when greater than 20 wt %, causes more electrolyte to be consumed and hinders migration of lithium ions, thus deteriorating the rate performance and cycling performance of the battery; and increasing of the coating amount of carbon nanotubes is conducive to improving the cycling performance and rate performance of the battery, however, excessive coating amount of carbon nanotubes in the negative electrode plate causes severe agglomeration of particles, thus leading to deterioration in full charge swelling rate of the battery.
For a difference from Example 1-1, refer to Table 3. For composition and amount of the commercial silicon oxide SiOx, conductive material 1, conductive material 2, polymer 1, and polymer 2, refer to Table 3. For particle size and conductivity of the negative electrode material, refer to Table 3-1. For cycling performance and discharge rate of the obtained battery, refer to Table 3-2.
For a difference from Example 1-1, refer to Table 3. For composition and amount of the commercial silicon oxide SiOx, conductive material 1, conductive material 2, polymer 1, and polymer 2, refer to Table 3. For particle size and conductivity of the negative electrode material, refer to Table 3-1. For cycling performance and discharge rate of the obtained battery, refer to Table 3-2.
Refer to Table 3-1. It can be learned from the comparisons between Example 1-1, Examples 3-1 and 3-2, and Comparative example 7 that the number of layers of graphene has no significant influence on the particle size of the negative electrode material; however, with the increasing number of layers of graphene, the conductivity of the negative electrode material decreases significantly.
Refer to Table 3-2. The comparisons between Example 1-1, Examples 3-1 and 3-2, and Comparative example 7 illustrate that with the increasing number of layers of graphene, the electrical conductivity of the battery decreases and the number of lithium ion transmission channels are reduced, thus leading to deterioration in cycling performance and rate performance of the battery; however, the number of layers of graphene has small influence on the full charge swelling rate of the battery.
For a difference from Example 1-1, refer to Table 4. For composition and amount of the commercial silicon oxide SiOx, conductive material 1, conductive material 2, polymer 1, and polymer 2, refer to Table 4. For particle size and conductivity of the negative electrode material, refer to Table 4-1. For cycling performance and discharge rate of the obtained battery, refer to Table 4-2.
For a difference from Example 1-1, refer to Table 4. For composition and amount of the commercial silicon oxide SiOx, conductive material 1, conductive material 2, polymer 1, and polymer 2, refer to Table 4. For particle size and conductivity of the negative electrode material, refer to Table 4-1. For cycling performance and discharge rate of the obtained battery, refer to Table 4-2.
Refer to Table 4-1. The magnitude of the flake diameter of graphene has small influence on the conductivity of the negative electrode material. However, it can be learned from the comparisons between Example 1-1, Examples 4-1 and 4-2, and Comparative examples 8 and 9 that increased flake diameter of graphene leads to more severe agglomeration of particles in the negative electrode material.
Refer to Table 4-2. The comparisons between Example 1-1, Examples 4-1 and 4-2, and Comparative examples 8 and 9 illustrate that the increasing of the flake diameter of graphene is more conducive to the presence of silicon-containing particles inside the graphene layer in the electrode material, suppressing swelling of the silicon-containing particles therein, and thereby improving the cycling performance of the battery and reducing the full charge swelling rate of the battery, however, the rate performance of the battery deteriorates. When the flake diameter of graphene increases to a specified value, especially when greater than 20 μm, a dispersion degree of graphene decreases and graphene cannot provide effective surface modification for the silicon-containing particles in the electrode material, leading to deterioration in cycling performance and full charge swelling rate of the battery.
For a difference from Example 1-1, refer to Table 5. For composition and amount of the commercial silicon oxide SiOx, conductive material 1, conductive material 2, polymer 1, and polymer 2, refer to Table 5. For particle size and conductivity of the negative electrode material, refer to Table 5-1. For cycling performance and discharge rate of the obtained battery, refer to Table 5-2.
Refer to Table 5-1. The comparisons between Example 1-1 and Examples 5-1 to 5-4 illustrate that, compared with graphene oxide, reduced graphene oxide used for the negative electrode material has poor dispersion effect, leading to poor surface modification for the silicon oxide and severe agglomeration of particles, but the conductivity of the negative electrode material is increased; and compared with single-walled carbon nanotubes, multi-walled carbon nanotubes used for the negative electrode material can reduce agglomeration of particles on the surface of the negative electrode material, but the conductivity of the negative electrode material is reduced to some extent.
Refer to Table 5-1 and Table 5-2. The comparisons between Example 1-1 and Examples 5-1 to 5-4 illustrate that, as compared with graphene oxide, the electrode material prepared using reduced graphene oxide has improved electrical conductivity, but ionic conductivity of the electrode material is reduced, leading to deterioration in cycling performance and rate performance of the battery; and as compared with single-walled carbon nanotubes, the electrode material prepared using multi-walled carbon nanotubes has reduced electrical conductivity, leading to deterioration in cycling performance of the battery to some extent.
Preparation steps of this example was basically the same as those of example 1-1, with the difference lying in that the “commercial silicon oxide SiOx (0.5<x<1.5, and =5 μm)” in step (I)-1 was replaced with “silicon compound SiOx particles containing an oxide layer (containing carbon)”, where a process for preparing finished silicon compound SiOx particles containing an oxide layer (containing carbon) was as follows.
(1) 100 g of commercial silicon oxide SiOx (0.5<x<1.5, and Dv50=5 μm), 2.2 g of a porogenic agent polyvinylpyrrolidone (PVP), and 0.5 g of an oxide precursor aluminum isopropoxide [Al(C3H7O)3] formed a mixed solution with the presence of 300 mL of an organic solvent ethanol and 1.5 g of deionized water;
(2) The silicon compound SiOx particles containing the oxide AlOy layer prepared in step (1), 300 mL of an organic solvent ethanol, and 10 g of a carbon precursor (obtained by mixing phenolic resin and a curing agent hexamethylenetetramine at a weight ratio of 9:1) were mixed to form a mixed solution;
For composition and amount of the commercial silicon oxide SiOx, conductive material 1, conductive material 2, polymer 1, and polymer 2, refer to Table 6. For particle size and conductivity of the negative electrode material, and metal percentage and thickness of the Al2O3 layer, refer to Table 6-1. For cycling performance and discharge rate of the obtained battery, refer to Table 6-2.
Refer to Table 6-1. The comparison between Example 1-1 and Example 6-1 illustrates that the silicon oxide particles further coated with the metal oxide Al2O3 has small influence on the particle size and conductivity of the negative electrode material.
Refer to Table 6-2. The comparison between Example 1-1 and Example 6-1 illustrates that the silicon oxide particles being coated first with the metal oxide Al2O3 and then with graphene and carbon nanotubes can further improve the cycling performance and rate performance of the battery.
For a difference from Example 1-1, refer to Table 7. For composition and amount of the commercial silicon oxide SiOx, conductive material 1, conductive material 2, polymer 1, and polymer 2, refer to Table 7. For particle size and conductivity of the negative electrode material, refer to Table 7-1. For cycling performance and discharge rate of the obtained battery, refer to Table 7-2.
For a difference from Example 1-1, refer to Table 7. For composition and amount of the commercial silicon oxide SiOx, conductive material 1, conductive material 2, polymer 1, and polymer 2, refer to Table 7. For particle size and conductivity of the negative electrode material, refer to Table 7-1. For cycling performance and discharge rate of the obtained battery, refer to Table 7-2.
Refer to Table 7-1. The comparisons between Example 1-1, Examples 7-1 to 7-3, and Comparative examples 10 to 12 illustrate that the increasing amount of polymer in the negative electrode material is conducive to improving dispersion uniformity of graphene and carbon nanotubes in the negative electrode plate, but deteriorates the conductivity of the powder in the negative electrode plate. It can be learned from Table 7-1 that different dispersing agents (CMC/PAA) used in Example 1-1 and Examples 7-4 to 7-6 has small influence on dispersion of graphene and carbon nanotubes in the negative electrode plate.
Refer to Table 7-1 and Table 7-2. The comparisons between Example 1-1, Examples 7-1 to 7-3, and Comparative examples 10 to 12 illustrate that the increasing amount of polymer in the negative electrode material improves dispersion uniformity of graphene and carbon nanotubes in the negative electrode plate, alleviates agglomeration of particles, and reduces the swelling rate of the battery, but deteriorates the rate performance of the battery. Excessively low amount (<0.1 g) of polymer leads to decreased dispersion uniformity of graphene and carbon nanotubes and severe agglomeration of particles in the negative electrode plate, resulting in significant deterioration in cycling, swelling, and rate performance of the battery; and excessively high amount (>10 g) of polymer leads to deterioration in dispersion effect of graphene and carbon nanotubes in the negative electrode plate, resulting in significant deterioration in cycling, swelling, and rate performance of the battery. The comparisons between Example 1-1 and Examples 7-4 to 7-6 illustrate that polymers of different types have small influence on performance of the battery.
Certainly, there may be various other embodiments of this application, and persons skilled in the art can make various corresponding changes and modifications according to this application without departing from the spirit and essence of this application. However, all such corresponding changes and modifications shall fall within the protection scope of this application.
This application is a continuation application of PCT/CN2020/140377, filed on Dec. 28, 2020, the disclosure of which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/CN2020/140377 | Dec 2020 | US |
| Child | 18342039 | US |
