CN110690426A - Composite lithium iron phosphate material for low-temperature rate discharge, positive plate and lithium ion battery - Google Patents
Composite lithium iron phosphate material for low-temperature rate discharge, positive plate and lithium ion battery Download PDFInfo
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Abstract
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a composite lithium iron phosphate material for low-temperature rate discharge, a positive plate and a lithium ion battery. The composite lithium iron phosphate material for low-temperature rate discharge is prepared by mixing the following components in percentage by mass and then sintering the mixture in a protective atmosphere: 5-10% of conductive carbon, 70-80% of lithium iron phosphate and 10-25% of lithium manganate. According to the invention, the interaction among the conductive carbon, the lithium iron phosphate and the lithium manganate is enhanced through sintering, the lithium ion migration resistance is reduced, and the low-temperature rate capability of the composite lithium iron phosphate material is improved.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a composite lithium iron phosphate material for low-temperature rate discharge, a positive plate and a lithium ion battery.
Background
The lithium iron phosphate material has the characteristics of good thermal stability, excellent cycle performance, high safety and the like, and is considered as a safe positive electrode material of a power lithium ion battery. However, the lithium iron phosphate material has poor low-temperature performance and rate charge and discharge performance due to low electronic conductivity and low lithium ion diffusion speed.
The application publication number of the invention is CN102394312A, which discloses a method for improving the low temperature performance of lithium iron phosphate, the method comprises the steps of using lithium manganate and lithium iron phosphate as positive electrode active materials, preparing the active materials, a conductive agent and a binder into slurry, and coating the slurry on a current collector to obtain a positive plate. In the method, the low-temperature performance of the positive active material is improved by adopting the lithium manganate, but the rate performance at low temperature is still poorer.
Disclosure of Invention
The invention aims to provide a composite lithium iron phosphate material for low-temperature rate discharge, which has better low-temperature rate performance.
The invention also aims to provide the positive plate which has better low-temperature rate capability.
The invention also aims to provide the lithium ion battery with better low-temperature rate performance.
In order to achieve the purpose, the composite lithium iron phosphate material for low-temperature rate discharge adopts the technical scheme that:
a composite lithium iron phosphate material for low-temperature rate discharge is prepared by mixing the following components in percentage by mass and then sintering the mixture in a protective atmosphere: 5-10% of conductive carbon, 70-80% of lithium iron phosphate and 10-25% of lithium manganate.
In the composite lithium iron phosphate material, the lithium manganate has a three-dimensional tunnel structure and high diffusion coefficient of the material, is beneficial to the insertion and extraction of lithium ions, and has better electronic conductivity (the conductivity is 10)-6S/cm) and ion conductivity, and the discharge plateau of lithium manganate is higher than that of lithium iron phosphate. Conductive carbon also has good electronic conductivity and certain ionic conductivity. The addition of the conductive carbon and the lithium manganate is favorable for improving a discharge voltage platform of the composite lithium iron phosphate material, increasing the electronic and ionic conductivity at low temperature and reducing the impedance, thereby improving the low-temperature dischargeElectrical platform and discharge capacity.
Meanwhile, in the sintering process, the stress in the mixing process of the lithium iron phosphate, the lithium manganate and the conductive carbon is eliminated, micropores and surface defects generated after the lithium iron phosphate, the lithium manganate and the conductive carbon are mixed are eliminated, the surface energy potential of the material is reduced, the contact area among the three materials is increased, the contact interface defects are reduced, the three materials are tightly combined, the resistance of lithium ions in the material is reduced, and therefore the multiplying power performance of the composite lithium iron phosphate is further improved. The composite lithium iron phosphate material can realize high-rate discharge of more than 1C at ultralow temperature of-45 ℃, and the discharge capacity retention rates of 1C and 3C at-45 ℃ are more than 75% and more than 64% respectively.
Since conductive carbon is a carbon material, sintering is performed in a protective atmosphere. The protective atmosphere used must be such as to prevent the carbon material from being oxidized during sintering and not affecting the other materials. Preferably, the protective atmosphere is an inert atmosphere such as a nitrogen atmosphere, an argon atmosphere, or the like. In order to save cost, the protective atmosphere is nitrogen atmosphere. Preferably, the used nitrogen is high-purity nitrogen, and the purity of the high-purity nitrogen is more than or equal to 99.999 percent.
The low-temperature rate capability of the prepared composite lithium iron phosphate material is further improved by optimizing the sintering temperature, preferably, the sintering temperature is 500-800 ℃. The medium-temperature sintering at 500-800 ℃ is adopted, so that on one hand, the defects of stress of lithium iron phosphate, lithium manganate and conductive carbon in the mixing process, micropores among materials and the like can be eliminated, and the resistance of lithium ions in the materials is reduced; on one hand, in the medium-temperature sintering process, the surface defects of the materials can be repaired, the surface energy potential of the materials is reduced, the contact area among the materials is increased, the contact interface defects are reduced, and the migration resistance of lithium ions on the surfaces of the materials is reduced; meanwhile, the sintering temperature is low, so that the growth of material grains is avoided, and the performance of the material is not influenced. Further preferably, the sintering temperature is 550-700 ℃.
In order to reduce energy consumption, the sintering time is 2-4 h.
The particle size of the lithium iron phosphate is smaller than that of lithium manganate, the particle size D50 of the lithium iron phosphate is not more than 2 mu m, and the particle size D50 of the lithium manganate is not more than 7 mu m. The lithium iron phosphate has small particle size and large particle size, and lithium manganate can be filled in large gaps among lithium iron phosphate particles, so that the migration distance of lithium ions is reduced. More preferably, the particle size of the lithium iron phosphate is 0.8 to 1 μm in terms of D50, and the particle size of the lithium manganate is 4 to 5 μm in terms of D50.
The conductive carbon is one or more of conductive carbon black, carbon nano tube, conductive graphite and carbon fiber. The conductive carbon is in a dot shape, a linear shape or a sheet shape, has smaller particle size, and can fill small gaps among lithium iron phosphate particles. In the composite lithium iron phosphate material, the lithium manganate is filled in large pores among lithium iron phosphate particles, the conductive agent is filled in small pores among the lithium iron phosphate particles, and the conductive agent, the lithium iron phosphate and the lithium manganate form a complete conductive network, so that the internal resistance of the composite lithium iron phosphate material is further reduced, and the low-temperature discharge capacity of the material is improved.
The positive plate adopts the technical scheme that:
the utility model provides a positive plate, includes the mass flow body and sets up the positive material layer on the mass flow body surface, including compound lithium iron phosphate material in the positive material layer, compound lithium iron phosphate material is above-mentioned compound lithium iron phosphate material that is used for low temperature multiplying power to discharge.
The positive electrode material layer in the positive plate comprises the composite lithium iron phosphate material, and the composite lithium iron phosphate material has low internal resistance and a complete conductive network, so that the internal resistance of the positive plate is low, and the positive plate has excellent low-temperature high-rate performance.
Preferably, the positive electrode material layer consists of the following components in percentage by mass: 93-95% of composite lithium iron phosphate material and 5-7% of binder. The binder used in the positive electrode sheet of the present invention is an oil-based binder such as polyvinylidene fluoride (PVDF) which is commonly used in the art.
The current collector used by the positive plate is a current collector commonly used in the prior art, such as an aluminum foil, a copper foil, a carbon-coated aluminum foil and the like. Preferably, the current collector is a carbon-coated aluminum foil. The carbon-coated aluminum foil can reduce the contact resistance between the current collector and the positive electrode material layer, and further increase the capacity of the positive electrode. The carbon-coated aluminum foil comprises an aluminum foil and a carbon layer coated on the surface of the aluminum foil. The thickness of the carbon layer is 2-4 mu m.
According to the prior art, the positive plate is provided with the tab. Preferably, the tab of the positive electrode sheet of the present invention is a single-sided full tab.
The preparation method of the positive plate comprises the following steps: uniformly mixing the composite lithium iron phosphate material, the binder and the N-methyl pyrrolidone, sieving with a 150-mesh sieve to prepare slurry, coating the slurry on a positive current collector, leaving a tab on one side white by 20nm, drying and rolling to obtain the lithium iron phosphate anode current collector.
The lithium ion battery adopts the technical scheme that:
a lithium ion battery comprises a positive plate and a negative plate, wherein the positive plate is the positive plate.
The lithium ion battery provided by the invention adopts the positive plate provided by the invention as the positive electrode, and has the advantages of good low-temperature rate performance, long cycle life and excellent safety performance.
A lithium ion battery generally consists of a positive plate, a negative plate, an electrolyte, a separator and a casing. The negative plate in the lithium ion battery comprises a negative current collector and a negative material layer arranged on the negative current collector, wherein the negative material layer mainly comprises the following components in percentage by weight: 92-95% of artificial graphite, 2-4% of conductive carbon black and 3-4% of a binder. The binder is a CMC/SBR composite binder (sodium carboxymethylcellulose/styrene butadiene rubber composite binder). The negative current collector is a copper foil. The preparation method of the negative pole piece comprises the following steps: 1) uniformly mixing the artificial graphite, the conductive carbon black and the binder according to the formula ratio to obtain a negative electrode mixture; 2) and (2) uniformly mixing the negative electrode mixture obtained in the step 1) with water to prepare slurry, coating the slurry on a negative electrode current collector, and drying to obtain the lithium ion battery.
The diaphragm in the lithium ion battery is any one of a PP diaphragm, a PE diaphragm and a PP/PE composite diaphragm. The thickness of the separator is not more than 20 μm. The shell is made of any one of an aluminum plastic film and metal aluminum.
Drawings
FIG. 1 is a discharge capacity curve at normal temperature for each of the lithium ion batteries of example 9 of the present invention and comparative example;
FIG. 2 is a plot of the rate discharge capacity at low temperature for lithium ion batteries of example 9 of the present invention and comparative example;
fig. 3 is a graph showing the comparative cycle curves of the lithium ion batteries of example 9 of the present invention and the comparative example at normal temperature.
Detailed Description
The present invention will be further described with reference to the following specific examples.
First, embodiment of composite lithium iron phosphate material for low-temperature rate discharge
Example 1
The composite lithium iron phosphate material of the embodiment comprises the following components in percentage by mass: 80% of lithium iron phosphate, 15% of lithium manganate, 2% of carbon nano tubes (the tube diameter is nano), and 3% of conductive carbon black (the particle size is nano), wherein the particle size of the lithium iron phosphate is D50-1 μm, and the particle size of the lithium manganate is D50-5 μm.
Taking lithium iron phosphate, lithium manganate, carbon nanotubes and conductive carbon black according to the mass percentage of each component, uniformly mixing, and then preserving heat for 2h at the temperature of 550 ℃ under the protection of a high-purity nitrogen atmosphere (the purity of nitrogen is more than or equal to 99.999%), thereby obtaining the composite lithium iron phosphate material of the embodiment.
Example 2
The composite lithium iron phosphate material of the embodiment comprises the following components in percentage by mass: 80% of lithium iron phosphate, 15% of lithium manganate, 1% of carbon nano tube (the tube diameter is nano), 3% of conductive carbon black (the particle diameter is nano), 1% of carbon fiber (the tube diameter is nano), wherein the particle diameter of the lithium iron phosphate is D50-1 μm, and the particle diameter of the lithium manganate is D50-4 μm.
Taking lithium iron phosphate, lithium manganate, carbon nanotubes, conductive carbon black and carbon fibers according to the mass percentage of each component, uniformly mixing, and then preserving heat for 2 hours at the temperature of 600 ℃ under the protection of a high-purity nitrogen atmosphere (the purity of nitrogen is more than or equal to 99.999 percent), thus obtaining the composite lithium iron phosphate material of the embodiment.
Example 3
The composite lithium iron phosphate material of the embodiment comprises the following components in percentage by mass: 70% of lithium iron phosphate, 25% of lithium manganate, 2% of carbon nano tubes (the tube diameter is nano), and 3% of conductive carbon black (the particle size is nano), wherein the particle size of the lithium iron phosphate is D50-1 μm, and the particle size of the lithium manganate is D50-4 μm.
Taking lithium iron phosphate, lithium manganate, carbon nano tubes and conductive carbon black according to the mass percentage of each component, uniformly mixing, and then preserving heat for 2.5 hours at the temperature of 600 ℃ under the protection of a high-purity nitrogen atmosphere (the purity of nitrogen is more than or equal to 99.999 percent), thus obtaining the composite lithium iron phosphate material of the embodiment.
Example 4
The composite lithium iron phosphate material of the embodiment comprises the following components in percentage by mass: 75% of lithium iron phosphate, 15% of lithium manganate, 2% of carbon nano tubes (the tube diameter is nano), 6% of conductive carbon black (the particle diameter is nano), and 2% of conductive graphite (the particle diameter is nano), wherein the particle diameter of the lithium iron phosphate is D50-0.8 μm, and the particle diameter of the lithium manganate is D50-5 μm.
Taking lithium iron phosphate, lithium manganate, carbon nanotubes, conductive carbon black and conductive graphite according to the mass percentage of each component, uniformly mixing, and then preserving heat for 3 hours at the temperature of 700 ℃ under the protection of a high-purity nitrogen atmosphere (the purity of nitrogen is more than or equal to 99.999 percent), thus obtaining the composite lithium iron phosphate material of the embodiment.
Second, embodiment of Positive electrode sheet
Example 5
The positive plate of the embodiment consists of a carbon-coated aluminum foil current collector and a positive material layer coated on the surface of the current collector. The positive electrode material layer comprises the following components in percentage by mass: 95% of the composite lithium iron phosphate material in the embodiment 1 and 5% of PVDF. The carbon-coated aluminum foil (the manufacturer is Guangzhou Nano new material science and technology Co., Ltd.) comprises an aluminum foil and a carbon layer coated on the surface of the aluminum foil, wherein the thickness of the carbon layer is 2 mu m.
The preparation method of the positive plate of the embodiment comprises the following steps: uniformly mixing the composite lithium iron phosphate material, the binder PVDF and the solvent N-methyl pyrrolidone, then sieving with a 150-mesh sieve to obtain slurry, uniformly coating the slurry on the surface of the carbon-coated aluminum foil, leaving a tab on one side white by 20nm, drying, and rolling to obtain the positive plate.
Example 6
The positive plate of the embodiment consists of a carbon-coated aluminum foil current collector and a positive material layer coated on the surface of the current collector. The positive electrode material layer comprises the following components in percentage by mass: 95% of the composite lithium iron phosphate material of the embodiment 2 and 5% of PVDF. The carbon-coated aluminum foil (the manufacturer is Guangzhou Nano new material science and technology Co., Ltd.) comprises an aluminum foil and a carbon layer coated on the surface of the aluminum foil, wherein the thickness of the carbon layer is 2 mu m.
The method for preparing the positive electrode sheet of this example was the same as the method for preparing the positive electrode sheet of example 5.
Example 7
The positive plate of the embodiment consists of a carbon-coated aluminum foil current collector and a positive material layer coated on the surface of the current collector. The positive electrode material layer comprises the following components in percentage by mass: 95% of the composite lithium iron phosphate material of the embodiment 3 and 5% of PVDF. The carbon-coated aluminum foil (the manufacturer is Guangzhou Nano new material science and technology Co., Ltd.) comprises an aluminum foil and a carbon layer coated on the surface of the aluminum foil, wherein the thickness of the carbon layer is 3 mu m.
The method for preparing the positive electrode sheet of this example was the same as the method for preparing the positive electrode sheet of example 5.
Example 8
The positive plate of the embodiment consists of a carbon-coated aluminum foil current collector and a positive material layer coated on the surface of the current collector. The positive electrode material layer comprises the following components in percentage by mass: 95% of the composite lithium iron phosphate material of the embodiment 4 and 5% of PVDF. The carbon-coated aluminum foil (the manufacturer is Guangzhou Nano new material science and technology Co., Ltd.) comprises an aluminum foil and a carbon layer coated on the surface of the aluminum foil, wherein the thickness of the carbon layer is 2 mu m.
The method for producing the positive electrode sheet of this example refers to the method for producing the positive electrode sheet of example 5.
Embodiments of the lithium ion Battery
Example 9
The lithium ion battery of the present embodiment comprises a positive plate, a negative plate, an electrolyte, a separator, and a case assemblyAnd (5) assembling. Wherein the positive electrode sheet is the positive electrode sheet of example 5. The diaphragm is a PP film with the thickness of 15 mu m, the shell is an aluminum plastic film, and the lithium salt in the electrolyte is LiPF6And LiFSI (total concentration of the two is 1.2mol/L, molar ratio is 4:1), and the electrolyte solvent is a mixture of EC, DMC and EMC (volume ratio of the three is 20: 50: 30).
The negative plate comprises a copper foil current collector and a negative material layer arranged on the surface of the copper foil, wherein the negative material layer comprises the following components in percentage by mass: 95% of artificial graphite, 2% of conductive carbon black and 3% of binder (CMC/SBR composite binder, wherein the mass ratio of CMC to SBR is 1: 2). The preparation method of the negative plate comprises the following steps: uniformly mixing artificial graphite, conductive carbon black and a binder to obtain a negative electrode mixture, uniformly mixing the negative electrode mixture and deionized water to prepare slurry, sieving the slurry with a 150-mesh sieve, coating the slurry on a copper foil, leaving a tab on one side white by 15nm, drying, pressing, and cutting to obtain the negative electrode plate.
The preparation method of the lithium ion battery of the embodiment comprises the following steps: winding the positive plate, the negative plate and the PP diaphragm into an integral battery core, packaging the battery core by using an aluminum plastic film (the packaging is one packaging), injecting electrolyte after vacuum drying, standing for 48 hours until the positive plate, the negative plate and the diaphragm are fully soaked by the electrolyte, and then forming an activated battery by charging and discharging, namely preparing the lithium ion battery of the embodiment.
Example 10
The lithium ion battery of the embodiment is formed by assembling a positive plate, a negative plate, electrolyte, a diaphragm and a shell. Wherein the positive electrode sheet is the positive electrode sheet of example 6. The separator was a PP film having a thickness of 20 μm, the case was an aluminum-plastic film, and the electrolyte was the same as in example 9. The negative electrode sheet was the same as that of example 9.
The method for preparing the lithium ion battery of this example is the same as that of example 9.
Example 11
The lithium ion battery of the embodiment is formed by assembling a positive plate, a negative plate, electrolyte, a diaphragm and a shell. Wherein the positive plate is the plate of example 7. The separator was a PP film having a thickness of 20 μm, the case was an aluminum-plastic film, and the electrolyte was the same as in example 9. The negative electrode sheet was the same as that of example 9.
The lithium ion battery of this example was prepared by reference to the preparation of example 9, except that: and standing for 42h after the electrolyte is injected, and keeping the same for the rest.
Example 12
The lithium ion battery of the embodiment is formed by assembling a positive plate, a negative plate, electrolyte, a diaphragm and a shell. Wherein the positive plate is the plate of example 8. The separator was a PE film having a thickness of 15 μm, the outer shell was made of aluminum metal, and the electrolyte was the same as in example 9. The negative electrode sheet was the same as that of example 9.
The method of manufacturing the lithium ion battery of this example refers to the method of manufacturing example 11, differing only in the separator used and the casing.
Fourth, comparative example
The lithium ion battery of the comparative example is assembled by a positive plate, a negative plate, electrolyte, a diaphragm (PP diaphragm) and a shell (aluminum-plastic film).
The preparation method of the positive plate comprises the following steps: uniformly mixing D50-1 mu m lithium iron phosphate, conductive carbon black, a binder PVDF (the mass percentages are 93 percent of the lithium iron phosphate, 3 percent of the conductive carbon black and 4 percent of the PVDF) and N-methyl pyrrolidone, sieving by a 150-mesh sieve, uniformly coating on the surface of a carbon-coated aluminum foil sold in a market, leaving a tab on one side white by 20nm, drying and rolling to obtain the positive pole piece.
The preparation method of the negative plate comprises the following steps: taking 94% by mass of artificial graphite, 2% by mass of conductive carbon black, 4% by mass of binder (CMC/SBR composite binder, the mass ratio of CMC to SBR is 1: 2) and deionized water, uniformly mixing to prepare slurry, sieving by a 150-mesh sieve, coating on a copper foil, leaving a tab on one side white by 15nm, drying, pressing, and cutting according to a required size to prepare the required negative pole piece.
The preparation method of the lithium ion battery of the comparative example comprises the following steps: and (3) winding the positive pole piece, the negative pole piece and the PP diaphragm (the thickness of the diaphragm is 24 mu m) into an integral electric core, packaging (sealing) by using an aluminum plastic film, injecting electrolyte (the electrolyte is the same as the embodiment 9) after vacuum drying, standing for 48 hours until the electrolyte fully infiltrates the positive pole piece, the negative pole piece and the diaphragm, and forming an activated battery by charging and discharging to obtain the lithium ion battery with comparison.
Fifth, test example
The discharge capacities of the lithium ion batteries of examples 9 to 11 and the lithium ion battery of the comparative example were tested at different temperatures and within the same voltage range, and the specific test procedure was: the battery was charged at 1C to 3.65V at normal temperature, and then discharged at 1C or 3C to 2.0V after standing at a test temperature for at least 8 hours, wherein the relative discharge capacity was (the discharge capacity of the battery of example/the discharge capacity of the battery of comparative example) × 100%, and the test results are shown in table 1 (the relative discharge capacities were calculated in the table as 1C discharge capacity at 25 ℃ in the lithium ion battery of comparative example).
The safety performance of the lithium ion batteries of examples 9 to 11 of the invention and the safety performance of the lithium ion batteries of the comparative examples were tested, and the specific test method was: overcharge, overdischarge, short circuit, extrusion, dropping, needling and heating tests were carried out according to the requirements of GB/T31485-2015, and the test results are shown in Table 1.
TABLE 1 test results of discharge capacity of lithium ion batteries of examples 9 to 10 and comparative example
("/" indicates test failed to start, no data record)
The normal temperature discharge capacity comparison curve of the lithium ion batteries of example 9 and comparative example is shown in fig. 1, the low temperature rate discharge capacity comparison curve of the lithium ion batteries of example 9 and comparative example is shown in fig. 2, and the comparative cycle curve of the lithium ion batteries of example 9 and comparative example at normal temperature (25 ℃) is shown in fig. 3.
The test results of the test examples show that compared with the prior art, the low-temperature discharge voltage platform of the composite lithium iron phosphate material is obviously improved, and as can be seen from fig. 1 and 2, the voltage at the temperature of minus 45 ℃ when discharging at 1C is 3.1-3.2V, and the voltage at the temperature of minus 45 ℃ when discharging at 3C is reduced, but the reduction range is small. As can be seen from fig. 2 and table 1, the composite lithium iron phosphate material of the present invention can realize a rate discharge of 1C or more at an ultralow temperature of-45 ℃, and the 1C and 3C discharge capacity retention rates are 75% or more and 64% or more, respectively. As can be seen from fig. 3, the composite lithium iron phosphate material of the present invention has the same stability as the pure lithium iron phosphate material. The composite lithium iron phosphate of the invention is as safe as pure lithium iron phosphate material, and has no fire or explosion under abuse conditions. The test results prove that the composite lithium iron phosphate material can adapt to a wider environment temperature range, can realize rate discharge at ultralow temperature and has practical application value.
Claims (10)
1. The composite lithium iron phosphate material for low-temperature rate discharge is characterized by being prepared by mixing the following components in percentage by mass and then sintering the mixture in a protective atmosphere: 5-10% of conductive carbon, 70-80% of lithium iron phosphate and 10-25% of lithium manganate.
2. The composite lithium iron phosphate material for low-temperature rate discharge according to claim 1, wherein the sintering temperature is 500-800 ℃.
3. The composite lithium iron phosphate material for low-temperature rate discharge according to claim 1 or 2, wherein the sintering time is 2-4 h.
4. The composite lithium iron phosphate material for low-temperature rate discharge according to claim 1 or 2, wherein the particle size of the lithium iron phosphate is smaller than that of lithium manganese oxide, wherein the particle size of the lithium iron phosphate is D50 ≤ 2 μm, and the particle size of the lithium manganese oxide is D50 ≤ 7 μm.
5. The composite lithium iron phosphate material for low-temperature rate discharge according to claim 1, wherein the conductive carbon is one or more of conductive carbon black, carbon nanotubes, conductive graphite and carbon fibers.
6. The positive plate is characterized by comprising a current collector and a positive material layer arranged on the surface of the current collector, wherein the positive material layer comprises a composite lithium iron phosphate material, and the composite lithium iron phosphate material is the composite lithium iron phosphate material for low-temperature rate discharge according to any one of claims 1 to 5.
7. The positive plate according to claim 6, wherein the positive material layer is composed of the following components in percentage by mass: 93-95% of composite lithium iron phosphate material and 5-7% of binder.
8. The positive plate according to claim 6 or 7, wherein the current collector is a carbon-coated aluminum foil, and the carbon-coated aluminum foil is composed of an aluminum foil and a carbon layer coated on the surface of the aluminum foil.
9. The positive electrode sheet according to claim 8, wherein the carbon layer has a thickness of 2 to 4 μm.
10. A lithium ion battery comprising a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet is the positive electrode sheet according to any one of claims 6 to 9.
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