Lithium iron silicate battery positive plate with composite coating structure

Abstract

The utility model discloses a kind of lithium silicate battery positive pole piece of composite coating structure, to solve lithium silicate electronic conductivity low, structural stability is poor and so on Problem.It uses "core-shell-layer" three-level composite coating structure: core layer is 50~200nm doped modified lithium silicate active particle;Inner layer is 5~15nm thick graphene / carbon nanotube+TiN / VO2 conductive coating;Outer layer is 10~20nm thick Al2O3 / Li3PO4 or PEO-LiTFSI stable coating layer.Prepared by sol-gel method, atomic layer deposition and other processes, continuous conductive network can be constructed, electrolyte corrosion is inhibited and ion transmission is optimized.The positive pole piece 0.1C capacity is close to theoretical value, 1C cycle 500 times attenuation rate is less than or equal to 10%, 5C capacity retention rate is greater than or equal to 70%, suitable for power battery and energy storage field, realize the synergistic promotion of conductivity and structural stability.

Description

Technical Field

[0001] This utility model belongs to the field of lithium battery cathode material technology, specifically relating to a composite-coated lithium iron silicate battery cathode sheet. Background Technology

[0002] Lithium iron silicate (Li2FeSiO4), as a cathode material for lithium batteries, possesses significant advantages such as high theoretical capacity (330 mAh / g), excellent safety, low cost, and environmental friendliness, making it a promising candidate for applications in power batteries and energy storage batteries. However, lithium iron silicate itself exhibits extremely low electronic conductivity (10⁻⁶ mAh / g). -14 ~10 -12 S / cm), small lithium-ion diffusion coefficient (10) -15 ~10 - 13 The battery suffers from problems such as low rate performance (cm² / s) and is prone to volume expansion and structural collapse during charge-discharge cycles, resulting in poor rate performance and short cycle life, which severely limits its commercial application.

[0003] To improve the performance of lithium iron silicate, existing technologies mostly employ single coating or doping modification methods. For example, carbon coating improves conductivity, but the carbon layer has poor stability and is prone to side reactions with the electrolyte during long-term cycling; coating with a single metal oxide enhances structural stability, but increases lithium-ion transport resistance. Single modification methods cannot simultaneously solve the problem of synergistic optimization of conductivity, structural stability, and ion transport efficiency. Therefore, there is an urgent need to develop a novel composite structure design to achieve a comprehensive improvement in the performance of lithium iron silicate cathode materials. Utility Model Content

[0004] The purpose of this invention is to provide a composite-coated lithium iron silicate battery cathode material to solve the defects of poor conductivity and insufficient structural stability of existing lithium iron silicate cathode materials.

[0005] The technical solution of this utility model to solve the above-mentioned technical problems is as follows: A composite-coated lithium iron phosphate battery cathode includes a core layer, an inner conductive coating layer, and an outer stabilizing coating layer arranged sequentially from the inside out. The cathode is made by coating a current collector with a mixture of composite coating particles, a binder, and a conductive agent. Carbon nanotubes are disposed within the inner conductive coating layer, penetrating into the core layer and overlapping each other to form a conductive network (i.e., a conductive channel) between the core layer and the inner conductive coating layer. A tab for electrical connection is mounted on the current collector side of the cathode body.

[0006] Furthermore, the carbon nanotubes penetrate the inner conductive coating layer and extend into the core layer, with the carbon nanotubes overlapping each other between the core layer and the inner conductive coating layer to form a conductive network structure.

[0007] Furthermore, the core layer, the inner conductive coating layer, and the outer stable coating layer constitute composite coated particles, and multiple composite coated particles are mixed with binder and conductive agent and coated to form a positive electrode coating.

[0008] This utility model has the following beneficial effects: Significantly improved conductivity: The inner layer of graphene / carbon nanotube composite carbon-based material constructs a continuous three-dimensional conductive network, which, together with nano-conductive oxides, optimizes interface conduction and effectively reduces electron transport resistance; Enhanced structural stability: The dense and stable outer coating layer can inhibit electrolyte erosion and dissolution of transition metal ions, while mitigating the volume expansion of active particles during charging and discharging, thus preventing structural collapse; High ion transport efficiency: The nanoscale core layer shortens the lithium-ion diffusion path, while the outer polymer electrolyte or highly ion-conductive inorganic coating layer ensures rapid lithium-ion transport and improves battery rate performance. Attached Figure Description

[0009] Figure 1 This is an exploded view of the structure of this utility model.

[0010] Figure 2 This is a cross-sectional view of the carbon nanotubes inserted into the core layer in this invention.

[0011] In the figure: 100, tab 101, inner conductive coating layer 200, carbon nanotube 201, core layer 300; Detailed Implementation

[0012] The principles and features of this utility model are described below with reference to the accompanying drawings. The examples given are only for explaining this utility model and are not intended to limit the scope of this utility model.

[0013] Example 1

[0014] 1. Core layer preparation: Fe(NO3)3·9H2O, Li2CO3, SiO2 and Mg(NO3)2 are mixed in stoichiometric ratio (Mg 2+ The doping amount is 5% of the molar number of Fe element. Citric acid is added as a chelating agent, and after dissolving in deionized water, it is stirred until a uniform sol is formed. The sol is dried at 80°C to form a gel. The gel is placed in an N2 atmosphere furnace and sintered at 750°C for 6 hours to obtain Mg-doped lithium iron silicate particles with a particle size of 100~150nm. 2. Inner conductive coating layer: The above particles were dispersed in a 0.8 mg / mL graphene / carbon nanotube (mass ratio 1:1) dispersion, ultrasonically treated for 45 min, vacuum filtered, and then mixed with TiN nanoparticles with a particle size of 3 nm (TiN mass is 1.5% of the composite particles). After spray drying, the mixture was calcined at 620℃ in N2 atmosphere for 2.5 h to form a conductive coating layer with a thickness of 8~10 nm. 3. Stable outer coating: An Al2O3 film is deposited on the surface of the conductive coated particles using atomic layer deposition technology. The deposition cycle is controlled to achieve a thickness of 15 nm and a porosity of <1%. 4. Positive electrode preparation: The composite coated particles were mixed with PVDF binder (6% by mass) and SuperP conductive agent (2.5% by mass) in a certain proportion. A slurry was prepared using N-methylpyrrolidone as a solvent, coated onto an aluminum foil current collector, vacuum dried at 120℃ for 12 hours, and then rolled to a density of 2.1 g / cm³. 3 Thus, a positive electrode sheet is obtained; 5. Performance Testing: The above-mentioned positive electrode sheet was assembled with a lithium metal negative electrode, a Celgard 2400 separator, and a 1 mol / L LiPF6-EC / DEC (volume ratio 1:1) electrolyte to form a CR2032 coin cell. Electrochemical performance was tested at 25℃: the discharge capacity at 0.1C rate was 312 mAh / g; the initial discharge capacity at 1C rate was 285 mAh / g, and the capacity after 500 cycles was 262 mAh / g, with a capacity decay rate of 8.1%; the discharge capacity at 5C rate was 202 mAh / g, with a capacity retention rate of 70.9%; AC impedance testing showed a charge transfer resistance of 35 Ω and a lithium-ion diffusion coefficient of 2.3 × 10⁻⁶. -12 cm 2 / s.

[0015] Example 2

[0016] 1. Core layer preparation: Fe(NO3)3·9H2O, Li2CO3, SiO2 and MnSO4 are mixed in stoichiometric ratio (Mn 2+ Mn-doped lithium iron silicate particles with a doping amount of 4% of Fe element were obtained by sintering at 780℃ under N2 atmosphere for 5h after sol-gel method. The particle size was 80~120nm. 2. Inner conductive coating layer: The particles were dispersed in a 0.6 mg / mL graphene / carbon nanotube (mass ratio 2:1) dispersion, ultrasonically treated for 50 min, filtered, and mixed with VO2 nanoparticles with a particle size of 4 nm (VO2 mass is 1% of the composite particles). After spray drying, the mixture was calcined at 640℃ in N2 atmosphere for 2 h to form a conductive coating layer with a thickness of 10~12 nm. 3. Outer layer stabilization coating: Polyethylene oxide and LiTFSI are mixed at a mass ratio of 8:1 and dissolved in acetonitrile to prepare a polymer solution. Conductive coating particles are dispersed in the solution, stirred and then vacuum filtered. The mixture is then vacuum dried at 80°C for 5 hours to form a PEO-LiTFSI coating layer with a thickness of 12~18nm. 4. Positive electrode preparation: Positive electrode sheets were prepared according to the binder and conductive agent ratios and process parameters in Example 1, with a roll density of 2.05 g / cm³. 3 ; 5. Performance Testing: Using the same assembled coin cells, the discharge capacity at 25℃ and a 0.1C rate was 308 mAh / g; the initial discharge capacity at 1C rate was 278 mAh / g, and after 500 cycles, the capacity was 256 mAh / g, with a capacity decay rate of 7.9%; the discharge capacity at 5C rate was 205 mAh / g, with a capacity retention rate of 73.7%; AC impedance testing showed a charge transfer resistance of 32 Ω and a lithium-ion diffusion coefficient of 3.1 × 10⁻⁶. -12 cm 2 / s.

[0017] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A composite-coated lithium iron silicate battery cathode sheet, characterized in that, It includes a core layer (300), an inner conductive coating layer (200), and an outer stable coating layer (100) arranged sequentially from the inside to the outside; the positive electrode is made by coating a current collector with a mixture of composite coating particles, binder, and conductive agent; carbon nanotubes (201) are provided in the inner conductive coating layer (200), and the carbon nanotubes (201) penetrate into the core layer (300); the positive electrode body has tabs (101) for electrical connection at its edge.

2. The composite-coated lithium iron phosphate battery cathode sheet according to claim 1, characterized in that, The carbon nanotubes (201) penetrate the inner conductive coating layer (200) and extend into the core layer (300). The carbon nanotubes overlap each other between the core layer and the inner conductive coating layer to form a conductive network structure.

3. The composite-coated lithium iron silicate battery cathode sheet according to claim 1, characterized in that, The core layer (300), the inner conductive coating layer (200), and the outer stable coating layer (100) constitute composite coated particles, and multiple composite coated particles are mixed with binder and conductive agent to form a positive electrode coating.

4. The lithium iron phosphate battery cathode sheet with a composite coating structure according to claim 1, characterized in that, The tab (101) is fixedly mounted on the side of the current collector of the positive electrode.

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