Secondary Battery Silicon Graphite Composite Sealing
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Solution Overview
Problem
Secondary batteries with silicon-based negative active materials face issues of volume expansion and contraction during charge and discharge cycles, limiting their service life, especially when packaged in a bag, and existing solutions do not adequately address high-temperature storage and safety performance.
Innovation Solution
A secondary battery design featuring a positive active material with single crystal particles and a negative active material comprising silicon-based and graphite materials, with a package bag sealing width of 3 mm to 8 mm, ensuring sufficient overcurrent capability and tensile resistance, and optimized particle sizes and porosity to enhance energy density, high-temperature storage, and safety performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If silicon-based materials are used as negative active material to improve energy density, then energy density is improved, but volume expansion and contraction during charge and discharge cycles occurs, limiting service life
Solution Approach 1:
The negative active material uses a composite structure of silicon-based material particles (15-30 mass%) embedded in a graphite material matrix, with silicon particles having 5-20 μm diameter and graphite particles having 3-10 μm diameter. This composite structure allows the high-capacity silicon to coexist with the stable graphite, which accommodates silicon's volume expansion/contraction, thereby maintaining both high energy density and long service life through synergistic material combination
Solution Approach 2:
The invention optimizes specific parameters including silicon particle diameter (5-20 μm), graphite particle diameter (3-10 μm), silicon content (15-30 mass%), and average negative active material particle size (7-15 μm). These parameter optimizations ensure adequate electrolyte penetration while maintaining structural stability during cycling, resolving the contradiction between achieving high energy density through silicon and maintaining service life
2Use of energy by moving object
If positive active material with high nickel content is used to improve energy density, then energy density is improved, but high-temperature storage performance and safety performance deteriorate
Solution Approach 1:
The positive active material employs a composite oxide structure Li[Ni_xCo_yMn_z]1-y-zO2 where multiple transition metals (Ni, Co, Mn) are combined in specific ratios (0.80≤x<0.95, 0.05<y≤0.20, 0.01<z≤0.10). This multi-element composite structure leverages Ni for high capacity, Co for electrical conductivity, and Mn for structural stability and thermal resistance, thereby achieving high energy density while maintaining excellent high-temperature storage performance and safety
Solution Approach 2:
The invention optimizes the local composition ratios of Ni, Co, and Mn within the spinel structure to create specific functional zones. The controlled distribution of these elements at atomic levels ensures that nickel provides high capacity locally while cobalt and manganese provide structural stability and thermal resistance in the same material phase, resolving the contradiction between energy density and high-temperature performance
3Strength
If package bag sealing width is increased to improve tensile resistance at tab welding position, then tensile resistance is improved, but overcurrent capability deteriorates
Solution Approach 1:
The invention optimizes the sealing width parameter to a specific range of 3-8 mm, which balances mechanical strength and electrical performance. This optimized sealing width provides sufficient tensile resistance at the tab welding position to prevent detachment during assembly and handling, while simultaneously maintaining adequate heat dissipation and current distribution characteristics to prevent overheating and ensure overcurrent protection capability
Data Source
AI summary
The application relates to a secondary battery comprising a package bag and a battery core arranged in the package bag, the battery core comprising a positive electrode plate, a negative electrode plate and a separator, the positive electrode plate comprising a positive current collector and a positive electrode film disposed on at least one surface of the positive electrode current collector and comprising a positive active material; and the negative electrode plate comprising a negative electrode current collector and a negative electrode film provided on at least one surface of the negative electrode current collector and comprising a negative active material, characterized in that the positive active material comprises one or more of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide, and at least a part of the positive active material comprises a single crystal particle; the negative active material comprises a silicon-based material and a graphite material; and the package bag has a sealing width of 3 mm to 8 mm.