Li-Ion Negative Electrode Coating for Capacity and Cycle Stability
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Solution Overview
Problem
Current Li-ion secondary batteries face challenges in achieving higher energy density and cycle characteristics due to the volume expansion of Si or SiO active materials during charging, which leads to reduction-decomposition of the electrolytic solution and capacity reduction, especially when coated with materials lacking Li-ion conductivity.
Innovation Solution
A negative electrode material is developed with thin coatings of a Li-containing oxide having high Li-ion conductivity, applied to Si or SiO particles, which regulates contact with the electrolytic solution and maintains Li-ion conduction, thereby suppressing reduction-decomposition and enhancing discharging capacity and cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Si or SiO particles are used as active material to increase discharging capacity, then energy density is improved, but volume expansion during charging causes reduction-decomposition of electrolytic solution and deteriorates cycle characteristics
Solution Approach 1:
A Li-containing oxide coating layer is introduced as an intermediary between the Si/SiO active material and the electrolytic solution. This coating layer mediates the interaction by preventing direct contact between the active material and electrolyte, thereby suppressing reduction-decomposition reactions while maintaining Li-ion conductivity for charge-discharge cycles.
Solution Approach 2:
A thin film coating of Li-containing oxide is applied to the surface of Si or SiO particles. This thin film acts as a protective shell that accommodates volume expansion during charging while preventing harmful reactions with the electrolytic solution, thus improving cycle characteristics without sacrificing capacity.
2Volume of moving object
If particle size is reduced to decrease volume expansion, then expansion is reduced, but surface activation promotes reduction-decomposition of electrolytic solution
Solution Approach 1:
The Li-containing oxide coating serves as a mediator that prevents direct contact between the highly active particle surfaces and the electrolytic solution. This intermediary layer suppresses the harmful reduction-decomposition reactions that occur when small, highly active particles contact the electrolyte, while still allowing Li-ion transport.
3Stability of the object's composition
If hard coating LixMyO is applied to decrease volume change, then capacity retention is improved, but Li-ion conductivity is poor causing capacity reduction and deterioration in rapid charging-discharging
Solution Approach 1:
The coating material composition is changed from conventional LixMyO to a Li-containing oxide with specific chemical composition and structure that possesses both protective properties and high Li-ion conductivity. This parameter change in material composition resolves the contradiction by providing both stability and fast ion transport.
Solution Approach 2:
A composite coating structure is formed using Li-containing oxide that combines the protective function (reducing volume change) with high Li-ion conductivity. The composite material approach allows simultaneous achievement of capacity retention and rapid charging-discharging performance.
4Reliability
If coating is applied to protect active material surface, then cycle characteristics are improved, but Li-ion conductivity decreases causing capacity reduction
Solution Approach 1:
The chemical composition and physical properties of the coating material are optimized to achieve the right balance: the Li-containing oxide coating has specific parameters (composition, thickness, crystalline structure) that enable it to be protective yet highly conductive to Li-ions, thus improving cycle characteristics without sacrificing capacity.
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 suppresses excessive reduction-decomposition, achieves a higher discharging capacity than graphite, and maintains excellent cycle characteristics, addressing the limitations of existing materials by ensuring stable and efficient Li-ion conduction.
Implementation Method 1
thin coatings of a Li-containing oxide having high Li-ion conductivity, applied to Si or SiO particles, which regulates contact with the electrolytic solution and maintains Li-ion conduction
Implementation Method 2
coatings of a Li-containing oxide...regulates contact with the electrolytic solution and maintains Li-ion conduction, thereby suppressing reduction-decomposition
Data Source
AI summary
The present invention provides a Li-ion secondary cell negative-electrode material with which it is possible to adequately suppress reductive decomposition of a liquid electrolyte by an active material during charging, the Li-ion secondary cell negative-electrode material exhibiting a high discharge capacity that exceeds the theoretical capacity of graphite and exceptional initial charging efficiency and cycle characteristics. In this negative-electrode material for a Li-ion secondary cell, the surfaces of particles of SiOx (O≤x<2) contain Li and at least one metallic element M selected from among Si, Al, Ti, and Zr, and have a coating of a Li-containing oxide comprising a composition in which M/Li>5 with respect to the molar ratio.