Lithium Silicate Coated Silicon Anode for Battery Efficiency
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Solution Overview
Problem
Non-aqueous electrolyte secondary batteries using silicon oxide as a negative-electrode active material face lower initial charge/discharge efficiency due to irreversible reactions and increased crystal grain sizes, leading to reduced lithium ion conductivity and capacity degradation over charge/discharge cycles.
Innovation Solution
A negative-electrode active material comprising a lithium silicate phase with silicon particles dispersed within, where the lithium silicate has a crystallite size of 40 nm or less, reducing the likelihood of irreversible reactions and enhancing lithium ion conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If SiOx is used as a negative-electrode active material to increase lithium ion intercalation capacity, then the volume change due to intercalation is reduced compared to Si, but the initial charge/discharge efficiency becomes lower due to irreversible reaction forming Li4SiO4
Solution Approach 1:
The patent applies preliminary action by pre-forming a lithium silicate phase coating on the SiOx particle surface before battery operation. This coating is created by heat treatment of a mixture containing SiOx and a lithium compound, which converts the surface SiO2 into lithium silicate in advance. This preliminary transformation prevents the harmful irreversible reaction during initial charging cycles while maintaining the desired volume stability.
Solution Approach 2:
The patent utilizes parameter changes by controlling the crystallite size of the lithium silicate phase to be 40 nm or less. By adjusting this critical size parameter, the material achieves optimal balance between preventing irreversible reactions (improving initial charge/discharge efficiency) and maintaining structural stability (controlling volume change). The nanoscale crystallite size is the key parameter that enables both benefits.
2Reliability
If heat treatment is performed to convert SiO2 into Li4SiO4 on particle surface, then initial charge/discharge efficiency is improved, but another high-temperature process is required for internal reaction which increases crystal grain sizes and reduces lithium ion conductivity
Solution Approach 1:
The patent resolves this contradiction by precisely controlling the crystallite size parameter of the lithium silicate phase to be 40 nm or less. This size control is achieved through optimized heat treatment conditions and particle size management. The nanoscale dimension prevents excessive crystal grain growth while ensuring complete conversion of SiO2 to lithium silicate, thereby improving initial charge/discharge efficiency without sacrificing lithium ion conductivity.
Solution Approach 2:
The patent applies preliminary action by performing the heat treatment process to form the lithium silicate phase before electrode assembly. This pre-treatment ensures that the conversion of SiO2 to lithium silicate is completed in advance under controlled conditions, preventing the need for additional high-temperature processing that would cause crystal grain growth. The preliminary formation creates the optimal nanostructured lithium silicate coating that maintains both efficiency and conductivity.
3Reliability
If crystal grain size of Si and Li4SiO4 is increased through high-temperature processing, then the irreversible reaction is suppressed, but volume change of active material particles increases and lithium ion conductivity is reduced
Solution Approach 1:
The patent resolves this contradiction by inverting the conventional approach: instead of increasing crystal grain size to suppress irreversible reactions, the patent uses nanoscale crystallite size (40 nm or less) of the lithium silicate phase. This size reduction actually enhances lithium ion conductivity while the lithium silicate phase itself prevents irreversible reactions through its stable structure. The key parameter change is using fine nanocrystals rather than large grains, which reverses the conventional wisdom while achieving both objectives.
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
This configuration improves initial charge/discharge efficiency and cycle characteristics by minimizing volume change and disintegration of the active material, resulting in better battery performance and longer cycle life.
Implementation Method 1
the volume change due to the intercalation of lithium ions is smaller in SiOx than in Si
Implementation Method 2
reduced lithium ion conductivity, for example
Implementation Method 3
SiOx is converted into Li4SiO4 (an irreversible reactant) in an irreversible reaction during charging and discharging
Data Source
AI summary
The initial charge/discharge efficiency and cycle characteristics of a non-aqueous electrolyte secondary battery that contains a silicon material as a negative-electrode active material are improved. A negative-electrode active material particle (10) according to an embodiment includes a lithium silicate phase (11) represented by Li2zSiO(2+z) {0<z<2} and silicon particles (12) dispersed in the lithium silicate phase (11). A lithium silicate constituting the lithium silicate phase has a crystallite size of 40 nm or less. The crystallite size is calculated using the Scherrer equation from the half-width of a diffraction peak of a (111) plane of the lithium silicate in an XRD pattern obtained by XRD measurement of the negative-electrode active material particle 10.