SiOx Negative Electrode Structure for Cycle-Stable Fast Charging
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Solution Overview
Problem
Conventional lithium ion secondary batteries using graphite as a negative electrode active material face challenges in further improving energy density, and the use of Si-based materials leads to expansion and contraction during charge and discharge, affecting cycle characteristics and rapid charging properties.
Innovation Solution
A negative electrode comprising a silicon-based active material (SiO x ) combined with specific carbon-based materials and a conductive additive, such as carbon nanotubes, is designed to manage expansion and contraction, enhancing electrical contact and reducing resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Si-based negative electrode active materials are used to increase capacity, then energy density is improved, but expansion and contraction during charge and discharge occur, deteriorating cycle characteristics
Solution Approach 1:
The patent embeds Si-based active material particles inside a composite structure consisting of conductive additive particles and binder material particles, forming a nested configuration where the Si-based material is surrounded and protected by the composite matrix. This nesting approach allows the Si-based material to expand and contract during charge-discharge cycles while maintaining electrical contact and structural integrity, thereby improving cycle characteristics without sacrificing capacity.
Solution Approach 2:
The patent creates a composite negative electrode active material consisting of Si-based active material particles combined with conductive additive particles and binder material particles in specific ratios. This composite structure provides both the high capacity of Si-based materials and the structural stability needed for good cycle characteristics, resolving the contradiction between capacity and reliability.
2Quantity of substance
If Si-based negative electrode active materials are used to improve energy density, then capacity increases, but rapid charging properties deteriorate due to expansion and contraction
Solution Approach 1:
The nested structure with conductive additives and binder material surrounding the Si-based particles maintains electrical pathways during rapid charge-discharge cycles, preventing the loss of conductive contact that would otherwise occur due to expansion and contraction. This enables both high capacity and good rapid charging properties.
Solution Approach 2:
The patent optimizes the particle size parameters of the Si-based active material (average particle diameter 3 nm to 30 nm) and the composite particles (average particle diameter 0.1 μm to 10 μm), as well as the composition ratios of conductive additive and binder material, to achieve a balance between capacity and rapid charging performance.
3Reliability
If graphite is used as negative electrode active material for safety and stability, then reliability is improved, but energy density cannot be further improved
Solution Approach 1:
The patent creates a composite negative electrode active material that combines Si-based particles with conductive additives and binder materials, achieving a balance between the high capacity of Si-based materials and the structural stability needed for safety and reliability, thereby overcoming the energy density limitation of pure graphite electrodes.
Data Source
AI summary
An objective of the present invention is to suppress the expansion and contraction when charging and discharging a nonaqueous electrolyte secondary battery, including lithium ion secondary batteries, when an Si-based negative electrode active material is used, to improve the lifespan (cycle characteristics) of the nonaqueous electrolyte secondary battery, and to improve rapid charging properties. The present invention is a negative electrode for a nonaqueous electrolyte secondary battery, the negative electrode containing a negative electrode active material, a binder, and a conductive additive. The negative electrode active material contains: a silicon-based active material (A) containing SiOx (in the formula, x is a number satisfying 0.5≤x≤1.6); a carbon-based active material (B) composed of secondary particles formed by aggregating primary particles; and a carbon-based active material (C) composed of primary particles different from the carbon-based active material (B). The average particle diameter of metallic silicon particles contained in the silicon-based active material (A) is 0.5-10nm, the conductive additive has a linear shape, the diameter of said line being is 1-4nm, and the length of the line being 2-15µm.