Lithium-Ion Anode Formation with 3D Si Network for Cycle Life
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Solution Overview
Problem
Lithium-ion batteries with silicon materials face challenges in cycle life and storage characteristics, as the silicon network's three-dimensional structure does not effectively manage volume changes and electrolyte decomposition during charging and discharging.
Innovation Solution
Incorporating a silicon alloy phase with a three-dimensional network structure and a silicate phase, where the silicate phase mitigates volume changes and electrolyte decomposition, and using a specific manufacturing method involving initial charging at controlled current rates to form an optimal network structure with an average mesh size of 2.8 nm to 3.5 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a silicon material is used as negative electrode active material, then specific capacity is large, but cycle life is short
Solution Approach 1:
The patent uses a composite material consisting of a silicon alloy phase (containing Li-Si alloy) with a three-dimensional network structure and a silicate phase (containing Li silicate). The silicate phase acts as a matrix that confines the silicon alloy phase, preventing excessive volume expansion during lithium insertion and extraction, thereby improving cycle life while maintaining high capacity
Solution Approach 2:
The patent creates a heterogeneous structure where different phases have different functions: the silicon alloy phase provides high lithium storage capacity, while the silicate phase provides structural stability and mitigates volume changes. This local differentiation of material properties resolves the contradiction between capacity and cycle life
2Productivity
If the three-dimensional network structure has high denseness, then Li transmission path is improved, but storage characteristics deteriorate
Solution Approach 1:
The patent optimizes the mesh size parameter of the three-dimensional network structure to a specific range (2.8 nm to 3.5 nm). This parameter optimization balances lithium ion transmission efficiency with structural stability during storage, preventing both excessive denseness (which would harm storage) and insufficient denseness (which would harm Li transmission)
3Quantity of substance
If the Si alloy phase expands and contracts with Li storage and release, then capacity is maintained, but volume change causes structural degradation
Solution Approach 1:
The silicate phase serves as a pre-established cushioning matrix that accommodates and constrains the volume changes of the silicon alloy phase during lithium insertion and extraction. This beforehand cushioning prevents structural degradation while allowing capacity-critical volume changes to 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
Improves storage characteristics and reduces capacity deterioration by maintaining an appropriate denseness of the three-dimensional network structure, enhancing the battery's overall performance.
Implementation Method 1
With the storage and release of Li, the Si alloy phase expands and contracts. It is considered that the silicate phase may mitigate the volume change of the Si alloy phase.
Implementation Method 2
Furthermore, it is considered that the silicate phase may impede the decomposition reaction of the electrolyte.
Implementation Method 3
It is considered that the three-dimensional network structure (Si alloy phase) also functions as a Li transmission path.
Data Source
AI summary
Manufacturing a lithium-ion battery includes assembling the lithium-ion battery; and performing an initial charging on the lithium-ion battery. The lithium-ion battery includes a positive electrode, a negative electrode, and an electrolyte; the negative electrode contains a negative electrode active material containing a precursor of a silicon material, the precursor having a composition represented by SiOx where a relationship of 0<x<2 is satisfied. The initial charging includes a first step where the charging is performed to an intermediate voltage at a first current rate, and a second step where the charging is performed from the intermediate voltage to a maximum voltage at a second current rate. The first current rate is lower than 0.5 C; the second current rate is higher than the first current rate; and the intermediate voltage is 3.75 V or higher.