Silicate-Coated Silicon Anode Material for Higher Initial Coulombic Efficiency
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Solution Overview
Problem
Existing negative electrode active materials for lithium-ion batteries, particularly those containing silicon, suffer from low initial coulombic efficiency due to the irreversible reaction between lithium and silicon oxide, leading to capacity retention issues.
Innovation Solution
A composite active material is developed, comprising silicon particles with an average size of 150 nm or less, a matrix phase, and a silicate compound of metals like Li, K, Na, Ca, Mg, or Al, where the silicate compound is concentrated near the surface of the silicon particles, enhancing the inhibition of lithium oxide formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-containing active materials are used as negative electrode materials, then the theoretical specific capacity is significantly improved (10 times or more higher than graphite), but the initial charge-discharge efficiency is reduced due to irreversible reaction between lithium and silicon oxide
Solution Approach 1:
The invention applies local quality by concentrating the silicate compound specifically at the near-surface region of silicon particles rather than uniformly distributing it throughout. This localized placement at the interface where lithium-silicon oxide reaction occurs maximizes the inhibition effect while minimizing the amount of silicate compound needed, thereby preserving bulk silicon capacity for lithium alloying reactions.
Solution Approach 2:
The silicate compound acts as an intermediary substance between lithium and silicon oxide. It forms a protective layer that mediates the interaction between these two components, preventing direct contact and irreversible reaction. The silicate compound specifically inhibits lithium oxide formation by blocking lithium's access to silicon oxide at the particle surface.
2Loss of energy
If Li or Mg compounds are added to silicon oxide to inhibit the reaction between lithium and silicon oxide, then the initial efficiency is improved, but the negative electrode active material structure becomes more complex and manufacturing difficulty increases
Solution Approach 1:
The invention employs parameter changes by controlling the particle size of silicon to 150 nm or less and adjusting the concentration and distribution of silicate compound to achieve optimal performance. By modifying these physical and chemical parameters, the invention simplifies the manufacturing process compared to adding multiple separate compounds, while still achieving effective inhibition of lithium-silicon oxide reaction.
3Speed
If the particle size of silicon is reduced to enhance lithium ion absorption and release, then the charge-discharge rate characteristics are improved, but the surface area increases leading to more pronounced irreversible reactions with lithium
Solution Approach 1:
The invention applies local quality by concentrating the silicate compound specifically at the near-surface region of silicon particles rather than uniformly distributing it throughout. This localized placement at the interface where lithium-silicon oxide reaction occurs maximizes the inhibition effect while minimizing the amount of silicate compound needed, thereby preserving bulk silicon capacity for lithium alloying reactions.
Solution Approach 2:
The silicate compound is pre-positioned on the silicon particle surface before lithium insertion occurs. This preliminary protective layer counteracts the harmful effect of increased surface reactivity by preemptively blocking lithium from reacting with silicon oxide, thus preventing irreversible lithium oxide formation before it can occur.
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 composite active material significantly improves the initial coulombic efficiency and capacity retention rate of the negative electrode, effectively mitigating the irreversible reaction between lithium and silicon oxide.
Implementation Method 1
lithium and silicon oxide present in the silicon-containing active material react with each other to form a lithium oxide during initial charging. The formed lithium oxide cannot be reversibly returned to a positive electrode during discharging. It is thought that lithium is lost by such an irreversible reaction, and initial charge-discharge efficiency is reduced.
Implementation Method 2
lithium intercalation compounds that can absorb and release lithium ions between the layers between crystal planes during charging and discharging
Implementation Method 3
negative electrode materials using metals such as silicon and tin, which are elements having high theoretical capacity and can absorb and release lithium ions
Implementation Method 4
initial charge-discharge efficiency is reduced. The methods described in PTL 1 to 4 attempt to inhibit the reaction between lithium and silicon oxide in the initial stage by containing Li or Mg in silicon oxide present in the silicon-containing active material
Data Source
AI summary
Provided is a composite active material for a secondary battery with improved initial coulombic efficiency and capacity retention rate of a negative electrode active material, and a secondary battery containing the composite active material for a secondary battery. The composite active material for a secondary battery has silicon particles with an average particle size of 150 nm or less, a matrix phase in which the silicon particles are dispersed, and a silicate compound of at least one metal selected from Li, K, Na, Ca, Mg, and Al. The composite active material for a second battery has the silicate compound in a near-surface of the silicon particles. The silicate concentration in the near-surface of the silicon particles is higher than the silicate concentration in the matrix phase. The composite active material for a secondary battery further has silicon dioxide in the near-surface of the silicon particles.