Electrochemical Device Volume Expansion Control
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Solution Overview
Problem
High-capacity negative active materials in electrochemical devices, such as silicon-based materials, experience significant volume expansion during cycling, leading to detachment and degradation of the active material layer, which compromises the cycle performance and energy density of electrochemical devices like lithium-ion batteries.
Innovation Solution
The electrochemical device is designed with a specific ratio of discharge capacity per unit area of the negative electrode to the positive electrode, controlled by adjusting parameters like charge cutoff voltage and mass ratios of active materials, to reduce volume expansion and improve cycle performance. This involves using lithium cobalt oxide or lithium nickel cobalt manganese oxide as positive active materials and silicon-based composites as negative active materials, along with conductive agents and binders to enhance stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high-capacity negative active materials (such as silicon-based materials) are used to increase energy density, then the energy density of the electrochemical device is improved, but significant volume expansion occurs during cycling, leading to detachment and chalking of the negative active material layer, thereby deteriorating cycle performance
Solution Approach 1:
The patent optimizes the mass ratio parameters of positive and negative active materials to specific ranges (positive active material mass ratio: 20-40%, negative active material mass ratio: 60-80%) to balance energy density and cycle performance. By controlling these compositional parameters, the device achieves high energy density while maintaining structural stability during cycling
Solution Approach 2:
The patent employs composite electrode structures where silicon-based negative active materials are combined with other materials (such as carbon-coated silicon or silicon oxide) to create a composite that maintains high capacity while reducing volume expansion. The positive electrode uses lithium cobalt oxide or lithium nickel cobalt manganese oxide composites to match the negative electrode's capacity ratio
2Reliability
If the mass ratio of positive to negative active material is increased to reduce volume expansion, then cycle performance is improved, but the energy density of the device decreases
Solution Approach 1:
The patent precisely controls the mass ratios of active materials within optimized ranges rather than using extreme values. The positive active material mass ratio is set to 20-40% and negative active material mass ratio to 60-80%, which balances the capacity ratio to achieve both high energy density and good cycle performance simultaneously
3Quantity of substance
If the charge cutoff voltage is increased to improve energy density, then the energy output is improved, but the positive electrode potential rises adversely affecting the positive active material and accelerating degradation
Solution Approach 1:
The patent optimizes the charge cutoff voltage to a specific range (4.20-4.45V) that balances energy density and material stability. This voltage optimization prevents excessive positive electrode potential that would cause material degradation while maintaining high energy output
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces volume expansion of the negative active material layer, maintains the stability of the positive active material, and enhances the cycle performance and energy density of the electrochemical device by optimizing the charge cutoff voltage and the mass ratio of active materials, thereby improving the overall performance of lithium-ion batteries.
Implementation Method 1
an electrochemical device includes a positive electrode plate, a negative electrode plate, and a separator disposed between the positive electrode plate and the negative electrode plate. The positive electrode plate includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer includes a positive active material.
Data Source
AI summary
This application provides an electrochemical device and an electronic device. The electrochemical device includes a positive electrode plate, a negative electrode plate, and a separator disposed between the positive electrode plate and the negative electrode plate. The positive electrode plate includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer includes a positive active material. The positive active material includes lithium cobalt oxide. The negative electrode plate includes a negative current collector and a negative active material layer disposed on the negative current collector. The negative active material layer includes a negative active material. The electrochemical device satisfies the following relational expressions: 3 ≤ 100 × (4.5 - U) - 10 × (CB - 1) ≤ 10, CB = (A' × B' × C')/(A × B × C) . By increasing the CB value of the electrochemical device and reducing the charge cutoff voltage U, the embodiments of this application reduce volume expansion of the negative active material layer during charging and discharging, prevent the rise of the positive electrode potential from adversely affecting the positive active material, and thereby improve the cycle performance of electrochemical device.