Lithium Silicate Silicon Composite Anode for Battery Efficiency
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Solution Overview
Problem
Non-aqueous electrolyte secondary batteries with silicon oxide (SiOx) as a negative-electrode active material suffer from lower initial charge/discharge efficiency due to irreversible reactions and increased crystal grain sizes, which lead to volume changes and reduced lithium ion conductivity.
Innovation Solution
A negative-electrode active material comprising a lithium silicate phase represented by Li2zSiO(2+z) with silicon particles dispersed within, having a porosity of 25% or less, which reduces the likelihood of irreversible reactions and minimizes volume changes during charging and discharging.
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 invention changes the chemical composition parameters by controlling the SiO2 content to 1 mass% or less and adjusting the Li content to achieve the specific formula range of Li2zSiO(2+z) where 0.5 ≤ z ≤ 2. This parameter optimization suppresses the formation of Li4SiO4 while maintaining structural stability, thereby improving initial charge/discharge efficiency without sacrificing volume change reduction
Solution Approach 2:
The invention creates a composite lithium silicate phase that combines SiOx with controlled Li content to form a new compound structure Li2zSiO(2+z). This composite material integrates the advantages of SiOx (lower volume change) while compensating for its disadvantage (irreversible reaction) through the specific compositional design and lithium silicate phase formation
2Reliability
If SiO2 is heat-treated at high temperature to convert it into Li4SiO4 in advance, then the initial charge/discharge efficiency is improved, but the crystal grain sizes of Si and Li4SiO4 increase, leading to increased volume change and reduced lithium ion conductivity
Solution Approach 1:
The invention changes the heat treatment parameters by lowering the temperature to 500°C or less and controlling the SiO2 content to 1 mass% or less. This parameter optimization prevents excessive crystal grain growth while still suppressing the formation of Li4SiO4, thereby maintaining small crystal grain sizes that ensure good lithium ion conductivity and minimal volume change
Solution Approach 2:
The invention performs preliminary heat treatment at low temperature (500°C or less) to pre-form the lithium silicate phase structure and suppress Li4SiO4 formation before battery assembly. This preliminary action at controlled temperature prevents subsequent high-temperature grain growth that would occur with conventional high-temperature treatment, maintaining fine crystal grain sizes
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 enhances the initial charge/discharge efficiency of non-aqueous electrolyte secondary batteries by minimizing particle disintegration and maintaining lithium ion conductivity, thereby improving battery performance.
Implementation Method 1
more lithium ions per unit volume can be intercalated into silicon materials, such as silicon (Si) and silicon oxides represented by SiOx, than into carbon materials, such as graphite
Implementation Method 2
improving the initial charge/discharge efficiency by heat-treating a mixture of SiOx and a lithium compound at high temperature to convert SiO2 into an irreversible reactant Li4SiO4 in advance
Data Source
AI summary
A non-aqueous electrolyte secondary battery that contains a silicon material as a negative-electrode active material has improved initial charge/discharge efficiency. A negative-electrode active material particle (10) according to an embodiment contains a base particle (13), which 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 base particle (13) has a porosity of 25% or less, preferably 15% or less.