CN-121983635-A - Lithium iron phosphate battery and preparation method thereof

CN121983635ACN 121983635 ACN121983635 ACN 121983635ACN-121983635-A

Abstract

The invention relates to the field of lithium batteries and discloses a lithium iron phosphate battery and a preparation method thereof, wherein the lithium iron phosphate battery comprises a positive electrode, a negative electrode, a diaphragm and electrolyte, a positive electrode material comprises carbon-coated lithium iron phosphate, the carbon-coated lithium iron phosphate comprises a lithium iron phosphate core and a carbon coating layer coated on the surface of the lithium iron phosphate core, the median particle diameter D50 of the lithium iron phosphate is 0.5-2 mu m, a negative electrode material comprises hard carbon-coated graphite, the hard carbon-coated graphite comprises a graphite core and a hard carbon coating layer coated on the surface of the graphite core, and the interlayer spacing of the hard carbon coating layer is 0.37-0.42nm. The lithium iron phosphate battery provided by the invention has the characteristic of quick charge and discharge, and simultaneously has good low-temperature performance.

Inventors

CHEN GANG
GAO DONGDONG
ZHANG MURONG
YUAN JINGHONG

Assignees

江苏海四达电源有限公司
江苏海四达储能科技有限公司
广东海四达新能源科技有限公司

Dates

Publication Date: 20260505
Application Date: 20241028

Claims (10)

1. The lithium iron phosphate battery is characterized by comprising an anode, a cathode, a diaphragm and electrolyte; the positive electrode material comprises carbon-coated lithium iron phosphate, wherein the carbon-coated lithium iron phosphate comprises a lithium iron phosphate core and a carbon coating layer coated on the surface of the lithium iron phosphate core, and in the carbon-coated lithium iron phosphate, the median particle diameter D50 is 0.5-2 mu m; the negative electrode material comprises hard carbon coated graphite, wherein the hard carbon coated graphite comprises a graphite core and a hard carbon coating layer coated on the surface of the graphite core, and the interlayer spacing of the hard carbon coating layer is 0.37-0.42nm.
2. The lithium iron phosphate battery of claim 1, wherein, In the positive electrode material, the median particle diameter D50 of the carbon-coated lithium iron phosphate is 0.7-1.7 mu m, the carbon coating layer content is 8.5-9.5wt%, and/or In the anode material, the interlayer spacing of the hard carbon coating layer is 0.38-0.40nm, the thickness of the hard carbon coating layer is 1-2nm, and the content of the hard carbon coating layer is 1-15wt%.
3. The lithium iron phosphate battery according to claim 1 or 2, wherein, The carbon-coated lithium iron phosphate is present in an amount of 95.5 to 97.5wt%, preferably 96 to 97wt%, based on the total weight of the positive electrode material, and/or The content of the hard carbon coated graphite is 94-97wt%, preferably 95-97wt%, based on the total weight of the negative electrode material; And/or The electrolyte comprises lithium salt, solvent and optional additives; the lithium salt comprises inorganic lithium salt and optional organic lithium salt, and/or In the electrolyte, the concentration of the lithium salt is 0.8-1.5mol/L; Preferably, the method comprises the steps of, The inorganic lithium salt is lithium hexafluorophosphate (LiPF 6 ), and/or The organic lithium salt is selected from one or more of lithium dioxalate borate (LiBOB), lithium bis (fluoro-sulfonyl) imide (LiFSI) and lithium bis (trifluoromethyl-sulfonyl) imide (LiTFSI); preferably, in the lithium salt, the content of the organic lithium salt is 0-20% based on the mole of lithium element; And/or The solvent is selected from at least two of Ethylene Carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (EMC), ethyl Propionate (EP) and Propyl Propionate (PP); And/or The additive is selected from Vinylene Carbonate (VC) and/or fluoroethylene carbonate (FEC); And/or Based on the total mass of the electrolyte, The content of the lithium salt is 10-14wt%, and/or The solvent content is 76-88wt%, and/or The content of the additive is 1-14wt%; And/or The diaphragm is selected from ceramic diaphragms.
4. A method for preparing the lithium iron phosphate battery according to any one of claims 1 to 3, comprising: (1) Forming a positive electrode slurry containing the carbon-coated lithium iron phosphate; (2) Forming a negative electrode slurry containing the hard carbon coated graphite; (3) Respectively coating positive electrode slurry and negative electrode slurry on a current collector, and rolling, die cutting and baking to obtain a positive electrode plate and a negative electrode plate; (4) Winding the positive plate, the negative plate and the diaphragm into a battery core, baking, and carrying out primary liquid injection, shelving, formation, shelving after formation, secondary liquid injection, final sealing and capacity division.
5. The method according to claim 4, wherein in the step (3), When the positive electrode slurry and the negative electrode slurry are respectively coated on the current collector, the positive electrode surface density is not more than 160g/m 2 , the negative electrode coating surface density is not more than 80g/m 2 , and/or In the rolling, the positive electrode compacted density is not higher than 2.4g/cc, and the negative electrode compacted density is not higher than 1.5g/cc.
6. The process according to claim 4 or 5, wherein in the step (4), The liquid injection coefficient is not lower than 3.8, preferably 4.5-5, and/or The liquid injection amount of the primary liquid injection accounts for 85-90wt% of the total liquid injection amount, and/or The liquid injection amount of the secondary liquid injection accounts for 10-15wt% of the total liquid injection amount.
7. The process according to any one of claims 4 to 6, wherein in the step (1), The viscosity of the positive electrode slurry is 6000-9000 Pa.s, and/or The solid content of the positive electrode slurry is not less than 58wt%, and/or The fineness of the positive electrode slurry is not higher than 8 mu m.
8. The production process according to any one of claims 4 to 7, wherein in the step (2), The viscosity of the negative electrode slurry is 2000-4000 Pa.s, and/or The solid content of the negative electrode slurry is 45-50wt%, and/or The fineness of the negative electrode slurry is not higher than 25 μm.
9. The production method according to any one of claims 4 to 8, wherein step (1) comprises: mixing carbon-coated lithium iron phosphate, a conductive agent, a binder and a solvent, adjusting viscosity, removing bubbles, and sieving to obtain anode slurry; Preferably, the conductive agent is a graphene composite conductive agent, the binder is polyvinylidene fluoride (PVDF), and/or The raw materials of the positive electrode slurry (without solvent) contain 95.5-97.5% of lithium iron phosphate, preferably 96-97%, 1.5-2.5% of conductive agent and 1.5-2.2% of binder.
10. The production method according to any one of claims 4 to 9, wherein step (2) comprises: Mixing hard carbon coated graphite, a conductive agent, a binder, an optional preservative and a solvent, adjusting viscosity, removing bubbles and sieving to obtain negative electrode slurry; preferably, the conductive agent is conductive carbon black (SP), the binder is sodium carboxymethylcellulose (CMC) and styrene butadiene rubber emulsion (SBR), the preservative is selected from ester emulsion, and/or In the raw materials of the negative electrode slurry (without solvent), the content of the hard carbon coated graphite is 94-97wt%, preferably 95-97wt%, the content of the conductive agent is 0.5-1.5wt%, the content of the binder is 2-4wt%, and the content of the retention agent is 0.1-1wt%.

Description

Lithium iron phosphate battery and preparation method thereof Technical Field The invention relates to the technical field of lithium batteries, in particular to a lithium iron phosphate battery and a preparation method thereof. Background The sales of new energy automobiles in China reaches 9.6 ten thousand vehicles in year 2024, and the sales are increased by 87% in the same proportion. The lithium ion battery is a material mainly applied to new energy automobiles at present, and along with the high-speed development of new energy automobiles in the future, the demand for the quick-charging lithium ion battery is increasing. The development of the current ternary rapid charging system is faster than that of the lithium iron phosphate rapid charging system, mainly because the ternary conductivity is better than that of the lithium iron phosphate. However, compared with a ternary system, the lithium iron phosphate system has the characteristics of low cost, high safety, no high-toxicity heavy metal ions and more stable structure, so that the development of the quick-charging battery of the lithium iron phosphate system has important significance for the development of new energy automobiles in the future. Disclosure of Invention The invention aims to provide a lithium iron phosphate battery and a preparation method thereof, wherein the lithium iron phosphate battery has the characteristic of quick charge and discharge and simultaneously has good low-temperature performance. According to a first aspect of the invention, the invention provides a lithium iron phosphate battery, which comprises a positive electrode, a negative electrode, a separator and electrolyte, wherein a positive electrode material comprises carbon-coated lithium iron phosphate, the carbon-coated lithium iron phosphate comprises a lithium iron phosphate core and a carbon coating layer coated on the surface of the lithium iron phosphate core, the median particle diameter D50 of the carbon-coated lithium iron phosphate is 0.5-2 mu m, a negative electrode material comprises hard carbon-coated graphite, the hard carbon-coated graphite comprises a graphite core and a hard carbon coating layer coated on the surface of the graphite core, and the interlayer spacing of the hard carbon coating layer is 0.37-0.42nm. According to a second aspect of the invention, the invention provides a preparation method of a lithium iron phosphate battery, which comprises the steps of (1) forming positive electrode slurry containing the carbon-coated lithium iron phosphate, (2) forming negative electrode slurry containing the hard carbon-coated graphite, (3) respectively coating the positive electrode slurry and the negative electrode slurry on a current collector, rolling, die cutting and baking to obtain a positive electrode plate and a negative electrode plate, (4) winding the positive electrode plate, the negative electrode plate and a diaphragm into a battery core, baking, and carrying out primary injection, shelving, formation, shelf after formation, secondary injection, final sealing and capacity division. In the lithium iron phosphate battery, the positive electrode adopts carbon coated lithium iron phosphate, so that the conductivity and the ion migration rate of the positive electrode can be improved, the negative electrode adopts hard carbon coated graphite, so that the dynamic performance of the negative electrode can be improved, and in a preferred embodiment, the effect of improving the conductivity of the electrolyte and the electrochemical performance of the battery can be improved by blending the proportions of the components in the electrolyte. In the preparation method of the lithium iron phosphate battery, process data such as sizing parameters, coating parameters, compaction, moisture requirements, liquid injection coefficients and the like are subjected to omnibearing research, so that the dynamic performance of the battery is improved in terms of the process. The lithium iron phosphate battery prepared by the most preferred scheme of the invention has excellent quick charge and quick discharge performance, can charge electric quantity from 20% to 80% in 9 minutes, has a capacity retention rate of 98.05% after being cycled for 150 weeks, and has good low-temperature performance, namely-10 ℃ and capacity retention rate of 104.62% after being cycled for 145 weeks at 0.1C. Drawings Fig. 1 is a graph of 4C/4C normal temperature charge-discharge cycle data of example 4, illustrating that the capacity retention rate of the lithium iron phosphate battery according to the present invention is 98.05% after 150 weeks of charge-discharge cycle at 4C under normal temperature conditions. Fig. 2 is a low temperature cycle chart of-10 ℃ in example 4, which illustrates that after the lithium iron phosphate battery of the invention is subjected to 0.1C charge/0.5C discharge cycle for 145 weeks under the condition of-10 ℃, the capacity retention rate can reach