SiOC-Silicon Anode Composition for Capacity and Cycle Stability
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Solution Overview
Problem
Current lithium ion secondary batteries face limitations in charge/discharge characteristics, initial coulombic efficiency, and cycle life due to the structural limitations of silicon oxycarbide (SiOC) materials, which suffer from volume expansion and contraction during lithium ion alloying, leading to disconnection of conduction paths and poor performance.
Innovation Solution
A negative electrode active material is developed comprising silicon-based inorganic compounds with specific chemical bonding states of silicon, oxygen, and carbon, where the silicon is in a specific chemical bonding state and carbon is present in a balanced form, forming a three-dimensionally entangled structure that supports zerovalent silicon particles, maintaining conduction paths and volume stability during charge/discharge cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If SiOC is complexed with silicon or silicon alloy to increase capacity, then charge/discharge capacity is improved, but cycle characteristics deteriorate due to volume expansion and contraction
Solution Approach 1:
The invention uses a composite structure where SiOC forms a ceramic skeleton that complexes with silicon or silicon alloy particles. This composite material approach allows the SiOC matrix to provide structural stability during volume expansion and contraction, preventing disconnection of conduction paths while maintaining high capacity from the silicon component.
Solution Approach 2:
The SiOC forms a flexible ceramic skeleton structure that can accommodate volume changes of the embedded silicon particles during charge/discharge cycles. This skeleton acts as a supportive framework that maintains structural integrity despite the expansion and contraction of the active silicon material.
2Reliability
If SiOC is used as inorganic binder with fine silicon particles, then initial coulombic efficiency is improved, but charge/discharge capacity remains low
Solution Approach 1:
The invention changes the structural parameters of SiOC by forming a ceramic skeleton with specific bonding configurations (Si-O-Si, Si-O-C, Si-C bonds) rather than using conventional SiOC structures. This parameter change enables the material to simultaneously achieve high initial coulombic efficiency and high charge/discharge capacity by optimizing the balance between structural stability and active material content.
3Stability of the object's composition
If conventional SiOC structure is used, then material stability is maintained, but charge/discharge characteristics are limited
Solution Approach 1:
The invention employs oxidation during the firing process to create a SiOC ceramic skeleton with enhanced Si-O bonding. The controlled oxidation creates a more stable ceramic structure with strong Si-O-Si and Si-O-C bonds that provide superior structural stability while maintaining electrochemical performance.
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 approach results in excellent charge/discharge characteristics, including high capacity, good initial coulombic efficiency, and improved cycle life, allowing for the use of larger silicon particles and enabling mass production with general-purpose pulverization techniques.
Implementation Method 1
silicon is in a specific chemical bonding state and carbon is in a specific chemical bonding state
Implementation Method 2
silicon-based material using silicon and an oxide thereof that can be alloyed with lithium ions
Implementation Method 3
firing the precursor (c) obtained in step 1 in an inert atmosphere at a maximum firing temperature in the temperature range of from 900° C. to 1250° C. inclusive
Implementation Method 4
obtaining a fired product (d) by firing the precursor (c)
Data Source
AI summary
An object of the present invention is to provide a negative electrode active material having excellent charge/discharge characteristics (charge and discharge capacities, initial coulombic efficiency, and cycle characteristics). The object is achieved by providing a negative electrode active material containing: a silicon-based inorganic compound (a) composed of silicon (excluding zerovalent silicon), oxygen, and carbon; and silicon (zerovalent) (b). The equivalent constituent ratio [Q units/(D units+T units+Q units)] indicating the chemical bonding state (D units [SiO2C2], T units [SiO3C], Q units[SiO4]) of the silicon (excluding zerovalent silicon) present in the silicon-based inorganic compound (a) is within the range of from 0.30 to 0.80 inclusive.