Silicon Nanoparticles in Lithium Silicate for Battery Efficiency
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Solution Overview
Problem
Non-aqueous electrolyte secondary batteries with 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 cycles.
Innovation Solution
A negative-electrode active material comprising a lithium silicate phase represented by Li2zSiO(2+z) with silicon particles dispersed within, where the silicon particles have 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
1Quantity of substance
If SiOx is used as a negative-electrode active material to increase lithium ion intercalation capacity, then the volume change during intercalation is reduced, but the initial charge/discharge efficiency decreases due to irreversible reaction forming Li4SiO4
Solution Approach 1:
The patent changes the crystallite size parameter of silicon particles to 40 nm or less, which fundamentally alters the reaction behavior. At this nanoscale dimension, the surface area to volume ratio increases dramatically, and the crystallite size becomes smaller than the diffusion length for lithium ions, preventing the formation of Li4SiO4 and enabling reversible reactions while maintaining high lithium ion intercalation capacity
Solution Approach 2:
The patent creates a composite structure where silicon particles with 40 nm or less crystallite size are dispersed in a lithium silicate phase matrix. This composite approach combines the high capacity of silicon with the stability of lithium silicate, preventing irreversible reactions while maintaining excellent lithium ion conductivity and cycle characteristics
2Reliability
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 decreases
Solution Approach 1:
The patent reverses the conventional approach by reducing crystallite size to 40 nm or less instead of increasing it through high-temperature processing. This nanoscale dimension prevents the volume expansion issues associated with larger crystals, as the small size allows for better accommodation of volume changes and maintains structural integrity during lithium ion insertion and extraction cycles
Solution Approach 2:
The patent employs a composite structure with silicon particles dispersed in lithium silicate phase, where the matrix provides structural support and prevents excessive volume change. This composite approach allows the silicon particles to maintain their nanoscale dimensions without undergoing the grain growth that would occur with high-temperature processing, thereby suppressing irreversible reactions while minimizing volume change
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 maintaining high lithium ion conductivity, resulting in better battery performance and capacity retention.
Implementation Method 1
silicon particles having a crystallite size of 40 nm or less, reducing the likelihood of irreversible reactions and enhancing lithium ion conductivity
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). The silicon particles (12) have a crystallite size of 40 nm or less. The crystallite size is calculated using the Scherrer equation from the half-width of the diffraction peak of the Si (111) plane in an XRD pattern obtained by XRD measurement of the negative-electrode active material particle 10.