High-capacity lithium iron phosphate energy storage battery and graphite cathode

Abstract

The invention discloses a high-capacity lithium iron phosphate energy storage battery and a graphite negative electrode, and relates to the technical field of electrochemical energy storage, the capacity of the battery is greater than 500 Ah, a positive electrode active material is graphite, a negative electrode active material is graphite, and a diaphragm base material is polypropylene or polyethylene; the surface of the graphite negative electrode is coated with an artificial solid electrolyte layer, so that electrolyte reduction, co-intercalation and thermal runaway reactions are inhibited; the artificial solid electrolyte layer has good ionic conductivity and electronic insulativity, can effectively improve the thermal stability of the battery, prolong the cycle life and improve the first coulombic efficiency, and still keeps good stability in a high-temperature environment; through the technical scheme, the safety, the stability and the economical efficiency of the high-capacity energy storage battery can be improved, and the high-capacity energy storage battery is particularly suitable for being applied to a large-scale energy storage system.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, and in particular to a high-capacity lithium iron phosphate energy storage battery and a graphite anode. Background Technology

[0002] To meet the frequency regulation and peak shaving needs of renewable energy power generation, electrochemical energy storage technology is constantly being updated and iterated. Currently, electrochemical energy storage systems are developing towards large capacity, low cost, and long lifespan. There are many reasons behind this development trend. On the one hand, with the continuous expansion and deepening of energy storage application scenarios, large-scale energy storage and long-term energy storage projects are placing higher demands on the capacity of battery cells. The scale of energy storage power stations will move towards a larger scale in the future. Therefore, battery cells need to have greater energy storage capacity to meet demand. On the other hand, cost factors are also crucial. In 2023, the price of raw materials dropped sharply, causing the price of energy storage cells to fluctuate and decline, making it increasingly urgent for companies to reduce costs. Large-capacity battery cells themselves have cost reduction advantages. During system integration, the number of batteries and components can be reduced, integration efficiency can be improved, and after-sales maintenance costs can be reduced, thereby significantly improving the economics of energy storage projects. To meet market demand, current energy storage cell manufacturers have increased the capacity of lithium iron phosphate energy storage cells from 280 Ah to 314 Ah, and the corresponding volumetric energy density has increased from 350 Wh / L to 390 Wh / L. In the future, the capacity of energy storage cells will be further increased to over 500 Ah, thereby enabling the volumetric energy density of the cells to reach 400 Wh / L. In the development of electrochemical energy storage, increasing cell capacity to achieve cost reduction and efficiency improvement is an important industry goal. At the same time, it is essential to address the safety risks brought about by capacity increases. As cells develop towards larger capacities, the increase in cell volume and energy density presents numerous challenges to heat dissipation. Uniform temperature distribution within the cell is difficult to achieve, leading to localized overheating. Furthermore, ensuring temperature consistency between cells is challenging. During long-term operation of the energy storage system, the temperature differences between cells will increase, which not only affects cell performance and lifespan but may also trigger serious safety accidents such as thermal runaway and fires. Such safety accidents can cause significant losses to energy storage system operators.

[0003] Research has revealed that the thermal runaway process of lithium iron phosphate batteries is triggered by side reactions of the electrolyte on the graphite anode. The thermal decomposition reaction of the electrolyte on the graphite anode also generates a large amount of gas, leading to an increase in the internal pressure of the battery, triggering the explosion-proof valve to open, causing thermal jetting, and thus affecting the safety of the module. In addition, the decomposition reaction of the electrolyte on the surface of the anode leads to a decrease in the battery's initial efficiency; the consumption of film-forming additives on the surface of the anode reduces the battery's cycle life; and the co-intercalation of some solvents with lithium ions on the graphite anode leads to a decline in the anode's capacity. Summary of the Invention

[0004] In view of the aforementioned existing problems, the present invention is proposed.

[0005] This invention provides a high-capacity lithium iron phosphate energy storage battery and a graphite anode to solve the problems of insufficient safety and stability of high-capacity lithium iron phosphate batteries caused by thermal runaway, electrolyte decomposition and co-intercalation issues in high-capacity anode materials.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: In a first aspect, embodiments of the present invention provide a high-capacity lithium iron phosphate energy storage battery, wherein the battery capacity is greater than 500 Ah, the positive electrode active material is LiFePO4, the negative electrode active material is graphite coated with artificial solid electrolyte, the separator substrate is polypropylene or polyethylene, and the positive electrode, separator and negative electrode are made into a cell by winding or stacking, and the cell packaging form includes square shell and blade.

[0007] Secondly, embodiments of the present invention also provide a graphite anode for a high-capacity lithium iron phosphate energy storage battery. The surface of the graphite anode is coated with an artificial solid electrolyte layer to suppress electrolyte reduction, co-intercalation and thermal runaway. The artificial solid electrolyte layer is directly coated onto the graphite surface before battery manufacturing.

[0008] As a preferred embodiment of the high-capacity lithium iron phosphate energy storage battery of the present invention, the graphite includes one or a combination of artificial graphite and natural graphite.

[0009] As a preferred embodiment of the graphite anode of the high-capacity lithium iron phosphate energy storage battery of the present invention, the artificial solid electrolyte layer has lithium conductivity and electronic insulation, and the artificial solid electrolyte layer is made of crystalline, partially crystalline and amorphous oxide materials.

[0010] As a preferred embodiment of the graphite negative electrode of the high-capacity lithium iron phosphate energy storage battery of the present invention, wherein the ionic conductivity σ of the artificial solid electrolyte layer satisfies 0.01<σ<1.1 mS / cm.

[0011] As a preferred embodiment of the graphite anode of the high-capacity lithium iron phosphate energy storage battery described in this invention, the artificial solid electrolyte layer does not exhibit significant chemical reactions when in contact with water, and does not produce residual alkali in an aqueous environment, thus satisfying the chemical stability required for the anode material during the aqueous slurry mixing process.

[0012] As a preferred embodiment of the graphite anode for a high-capacity lithium iron phosphate energy storage battery according to the present invention, the anode powder is subjected to elemental analysis, wherein the content of La element M is... La With Zr element content M Zr Satisfying 1.3 < M La / Mzr <2.6, where M La and M Zr The unit is mol / L; if La and Zr are absent, the mass percentage of Al is less than 1 wt%. As a preferred embodiment of the graphite anode of the high-capacity lithium iron phosphate energy storage battery described in this invention, the artificial solid electrolyte coating layer and graphite in the anode material satisfy the following relationship: 1x10 -9 ≤M i / (M g ρS g )≤1x10 -8 M i The mass of the artificial solid electrolyte coating layer is expressed in grams (g); M g ρ is the mass of graphite, in grams; ρ is the density of the artificial solid electrolyte coating layer, in g / m³. 3 S g Specific surface area of ​​graphite, in m² 2 / g.

[0013] As a preferred embodiment of the graphite anode of the high-capacity lithium iron phosphate energy storage battery described in this invention, wherein: in the anode material, the powder compaction density P of the material and the mass fraction Wi of the artificial solid electrolyte coating layer satisfy 1.6 < P < 1.7 - 10 × Wi, where the unit of P is g / m³ and the unit of Wi is .

[0014] As a preferred embodiment of the high-capacity lithium iron phosphate energy storage battery described in this invention, the negative electrode material is mixed with solvent, conductive agent, dispersant and binder to form a slurry, coated into an electrode roll, rolled and then cut into electrode sheets, which are then wound or stacked together with the positive electrode sheet and separator to form a square or blade cell with a cell capacity greater than 500 Ah.

[0015] The beneficial effects of this invention are as follows: This invention is the first to propose using a coated graphite anode in lithium iron phosphate cells with a capacity greater than 500 Ah to improve battery safety. 1. The use of graphite anodes coated with artificial solid electrolyte layers increases the thermal runaway reaction trigger temperature of the battery by 50-70°C, delays the occurrence of thermal runaway reaction in lithium iron phosphate batteries, and improves battery safety.

[0016] 2. By optimizing the coating amount and coating process, the capacity, powder resistivity and compaction density of the coated graphite material did not decrease significantly compared with bare graphite, thus ensuring the energy density and rate performance of the battery.

[0017] 3. The coating of artificial solid electrolyte layer improves the stability of the negative electrode interface, prevents electrolyte decomposition and co-intercalation at the negative electrode, and improves the battery's initial coulombic efficiency and cycle performance. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the graphite-coated artificial solid electrolyte layer in Example 1. Detailed Implementation

[0020] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0021] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0022] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0023] Artificial solid electrolyte layer (SEI) is constructed on the surface of graphite anode, such as... Figure 1 As shown, the artificial solid electrolyte layer constructed using inorganic materials with ionic conductivity and electronic insulation exhibits high thermal stability and does not decompose at high temperatures. This effectively inhibits electrolyte decomposition and co-intercalation, thereby improving interface stability and battery safety.

[0024] Example 1, referring to the figure, is the first embodiment of the present invention. This embodiment provides a high-capacity lithium iron phosphate energy storage battery and a graphite anode, comprising: 1. An artificial solid electrolyte layer is coated onto the surface of graphite. The graphite can be one or a combination of artificial and natural graphite. The artificial solid electrolyte layer is an inorganic material that does not undergo thermal decomposition and possesses ionic conductivity and electronic insulation. The artificial solid electrolyte layer is coated onto the graphite surface before battery fabrication.

[0025] 2. Select suitable materials as coating layers based on the electrochemical window, such as β-Al₂O₃ and Li₇La₃Zr₂O. 12Etc. Ensure the electrochemical stability of the coating material at the negative electrode.

[0026] 1) Preferably, the ionic conductivity σ of the artificial solid electrolyte layer satisfies 0.01 < σ < 1.1 mS / cm.

[0027] 2) Preferably, the artificial solid electrolyte layer has good stability with water and does not produce residual alkali, thus meeting the requirements of the negative electrode aqueous slurry.

[0028] 3. Optimize the coating amount to ensure that the resistivity and compaction density of the graphite anode powder do not decrease significantly while forming a uniform coating on the graphite surface, thus guaranteeing the rate performance and volumetric energy density of the battery. Summarize the empirical relationship between coating amount, coating material density, and graphite specific surface area to form an empirical equation for calculating the optimal coating amount.

[0029] The empirical relationships are as follows: 1) Elemental analysis of the negative electrode powder was performed, and the content of La element M was determined. La With Zr element content M zr Satisfying 1.3 < M La / M zr <2.6, where M La and M zr The unit is mol / L; if La and Zr elements are absent, the mass percentage of Al is less than 1 wt%.

[0030] 2) Powder compaction density P of the material and mass fraction W of the artificial solid electrolyte coating layer i The condition 1.6 < P < 1.7 - 10 × W is satisfied. i The unit of P is g / m³. 3 W i The unit is %.

[0031] 3) The artificial solid electrolyte coating layer and graphite in the negative electrode material satisfy the following relationship: 1x10 -9 ≤M i / (M g ρS g )≤1x10 -8 M i The mass of the artificial solid electrolyte coating layer is expressed in grams (g); M g ρ is the mass of graphite, in grams; ρ is the density of the artificial solid electrolyte coating layer, in g / m³. 3 S g Specific surface area of ​​graphite, in m² 2 / g.

[0032] 4. Based on the above-mentioned graphite anode material, develop energy storage cells with a capacity of >500 Ah. The structure is not limited to winding and stacking, and the packaging form is not limited to square shell and blade.

[0033] The high-capacity lithium iron phosphate energy storage battery provided by this invention effectively solves the problems of battery thermal runaway, electrolyte decomposition on the negative electrode surface, and performance degradation caused by co-intercalation in the prior art by coating the graphite negative electrode surface with an artificial solid electrolyte layer. Specifically, the technical solution of this invention has the following effective effects: Enhancing battery safety: The coating of the artificial solid electrolyte layer effectively suppresses the reduction and decomposition reactions of the electrolyte on the negative electrode surface, reducing the risk of thermal runaway inside the battery and improving battery safety. Under high-temperature environments, the battery's thermal stability is significantly improved, and the temperature at which thermal runaway occurs is delayed to 80-100°C, significantly enhancing battery safety.

[0034] Improved battery performance: The coating layer effectively prevents electrolyte decomposition and co-intercalation, improving the battery's initial coulombic efficiency and significantly enhancing cycle performance. By optimizing the coating amount and process, the battery's energy density and rate performance are ensured, avoiding negative effects caused by excessive use of the coating layer.

[0035] Extended battery life: By forming a stable artificial solid electrolyte layer on the graphite anode surface, battery capacity degradation is reduced, and cycle life is extended. The battery maintains high stability during long-term use, significantly reducing performance degradation caused by thermal runaway and electrolyte decomposition.

[0036] Improving battery economics: This technical solution reduces the number of batteries and components required in the battery system by enhancing the performance of the graphite anode, thereby reducing the complexity and cost of system integration and improving the economics of the energy storage system. In system integration, by improving battery capacity and performance, long-term maintenance costs are reduced, further enhancing the battery's market competitiveness.

[0037] Broad application prospects: This technology is suitable for high-capacity energy storage batteries, especially in large-scale energy storage systems, meeting the demands for high capacity, low cost, and long lifespan, aligning with current trends in energy storage technology development. With further increases in battery capacity (exceeding 500 Ah), this technology will better adapt to the future energy storage market's higher performance requirements.

[0038] In summary, the technical solution of this invention effectively solves the problems of thermal stability, battery life and safety of existing large-capacity lithium iron phosphate energy storage batteries, significantly improves the performance, stability and economy of the battery, and has great market application potential and broad industrial prospects.

[0039] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A high capacity lithium iron phosphate energy storage battery, characterized in that, The capacity of the battery is greater than 500 Ah, the positive active material is LiFePO4, the negative active material is graphite coated with an artificial solid electrolyte layer, the separator substrate is polypropylene or polyethylene, the positive electrode, the separator and the negative electrode are made into an electric core by winding or stacking, and the packaging form of the electric core includes a square shell and a blade.

2. A graphite negative electrode of a large-capacity lithium iron phosphate energy storage battery, based on the large-capacity lithium iron phosphate energy storage battery of claim 1, characterized in that, The surface of the graphite negative electrode is coated with an artificial solid electrolyte layer to inhibit electrolyte reduction, co-intercalation and thermal runaway, and the artificial solid electrolyte layer is directly coated on the surface of the graphite before the battery is made.

3. A high capacity lithium iron phosphate battery as claimed in claim 1 wherein, The graphite includes one or a combination of both of artificial graphite and natural graphite.

4. A high capacity lithium iron phosphate battery graphite negative electrode as claimed in claim 2, wherein, The artificial solid electrolyte layer has lithium conduction ability and is electronically insulating, and the artificial solid electrolyte layer is selected from crystalline, partially crystalline and amorphous oxide materials.

5. A high capacity lithium iron phosphate battery graphite negative electrode as claimed in claim 4, wherein, The ionic conductivity σ of the artificial solid electrolyte layer satisfies 0.01 < σ < 1.1 mS / cm.

6. A high capacity lithium iron phosphate battery graphite negative electrode as claimed in claim 4 wherein, When the artificial solid electrolyte layer is in contact with water, no obvious chemical reaction occurs, and no residual alkali is generated in a water environment.

7. A high capacity lithium iron phosphate battery graphite anode as claimed in claim 2 wherein, Elemental analysis is performed on the negative electrode powder, wherein the content M of La element La and the content M of Zr element Zr satisfies 1.3 < M La / M zr < 2.6, wherein M La and M Zr are in mol / L; if no La element and Zr element exist, the mass percentage of Al element is less than 1wt%. ​ 8. A high capacity lithium iron phosphate battery graphite anode as claimed in claim 2, wherein, The artificial solid electrolyte coating layer in the negative material and the graphite satisfy the following relationship: 1x10 -9 ≤M i / (M g ρS g )≤1x10 -8 , wherein M i is the mass of the artificial solid electrolyte coating layer, in g; and M g is the mass of the graphite, in g. p is the density of the artificial solid-state electrolyte coating layer in g / m 3 ; S g Specific surface area of graphite, in m 2 / g.

9. A high capacity lithium iron phosphate battery graphite anode as claimed in claim 2 wherein, In the negative electrode material, the powder compaction density P of the material and the mass fraction Wi of the artificial solid electrolyte coating layer satisfy 1.6 < P < 1.7-10×Wi, wherein the unit of P is g / m³ and the unit of Wi is %. ​ 10. A high capacity lithium iron phosphate battery as claimed in claim 1 wherein, The negative electrode material is mixed with a solvent, a conductive agent, a dispersant and a binder to form a slurry, which is coated into an electrode roll, rolled and then cut into electrode sheets, which are wound or stacked with positive electrode sheets and separators to form square shell or blade electric cores, and the capacity of the electric core is greater than 500 Ah.

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