SiOx Negative Electrode Conductivity and Cycle Life
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Solution Overview
Problem
Lithium ion secondary batteries with SiOx negative electrode materials face rapid degradation due to volume changes during charge and discharge, leading to deteriorated battery characteristics, particularly in conductivity and cycle life.
Innovation Solution
A lithium ion secondary battery design incorporating a negative electrode with SiOx active material, where the atomic ratio of O to Si is 0.5<x<1.5, combined with a nonaqueous electrolyte at a concentration exceeding the conductivity maximum, and a conductive carbon material composite to form a stable conductive network, minimizing electrolyte salt consumption and enhancing charge-discharge cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If SiOx is used as negative electrode active material to increase capacity, then charge-discharge capacity is improved, but volume change during charge and discharge causes rapid deterioration of battery characteristics
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte by using a specific mixed solvent system (cyclic carbonate and chain carbonate in 1:4 to 1:9 volume ratio) and controlling the concentration of lithium salt to exceed the point of maximum conductivity. This parameter optimization reduces electrolyte decomposition and improves battery cycle characteristics while maintaining high capacity.
Solution Approach 2:
The patent employs a composite electrolyte system combining cyclic carbonate (EC or PC) and chain carbonate (DMC, DEC, or EMC) in specific volume ratios. This composite solvent system provides both high dielectric constant (from cyclic carbonate) and low viscosity (from chain carbonate), achieving optimal ion conductivity and stability for SiOx-based electrodes.
2Reliability
If electrolyte salt concentration is increased to improve conductivity, then electrical conductivity is improved, but excessive concentration causes deviation from optimal performance
Solution Approach 1:
The patent identifies and exploits the non-monotonic relationship between electrolyte salt concentration and conductivity. By controlling the lithium salt concentration to exceed the maximum conductivity point (e.g., >1.0 mol/L for LiPF6 in EC/DMC), the patent achieves a balance where sufficient conductivity is maintained while electrolyte decomposition is reduced, improving overall battery performance and cycle life.
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 battery exhibits improved charge-discharge cycle characteristics and increased capacity by maintaining conductivity and reducing electrolyte salt consumption, thereby extending the battery's lifespan and performance.
Implementation Method 1
a nonaqueous electrolyte containing at least an electrolyte salt and an organic solvent
Implementation Method 2
materials such as silicon (Si) and tin (Sn) that are capable of occluding and releasing more lithium (ions)
Data Source
AI summary
A lithium ion secondary battery containing a negative electrode active material containing Si and O as constituent elements and exhibiting excellent charge-discharge cycle characteristics. The lithium ion secondary battery has a positive electrode having a positive electrode material mixture layer, a negative electrode, a separator and a nonaqueous electrolyte containing at least an electrolyte salt and an organic solvent, where the negative electrode has a negative electrode material mixture layer containing a negative electrode active material containing Si and O as constituent elements (the atomic ratio x of O to Si is 0.5≦x≦1.5). The nonaqueous electrolyte contains the electrolyte salt at a concentration exceeding a concentration at which conductivity in the nonaqueous electrolyte containing the electrolyte salt and the organic solvent is maximized, and the conductivity at 25° C. is 6.5 to 16 mS/cm.