Silicon-Composite Anode Material for Stable Li-Ion Cycling
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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 issues during lithium ion alloying, leading to disconnection of conduction paths and poor performance.
Innovation Solution
A negative electrode active material composed of silicon-based inorganic compounds with specific chemical bonding states, including silicon (excluding zerovalent silicon), oxygen, and carbon, where the equivalent constituent ratio of chemical bonding units is within the range of 0.30 to 0.80, and the presence of free carbon in a specific state, forming a three-dimensionally entangled structure to support zerovalent silicon particles and maintain conduction paths during charge/discharge cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon particles are used to increase capacity, then charge/discharge capacity is improved, but volume expansion and contraction cause disconnection of conduction paths and deteriorate cycle characteristics
Solution Approach 1:
The patent applies this principle by forming a flexible carbon coating film on the silicon particles. This carbon shell accommodates the volume expansion and contraction of silicon during charge/discharge cycles while maintaining structural integrity and continuous conduction paths, thereby improving cycle characteristics without sacrificing capacity
Solution Approach 2:
The patent uses composite materials by combining silicon particles with carbon-containing materials to form a composite structure. This composite approach allows the silicon to provide high capacity while the carbon component provides structural stability and maintains conduction paths during volume changes, resolving the contradiction between capacity and cycle life
2Reliability
If SiOC is used as negative electrode material, then charge/discharge cycle characteristics are improved, but charge and discharge capacities and initial coulombic efficiency remain low
Solution Approach 1:
The patent merges SiOC material with silicon particles or silicon alloy particles to create a composite negative electrode material. This combination allows the SiOC to provide good cycle characteristics while the silicon components contribute high charge and discharge capacities, achieving both goals simultaneously
Solution Approach 2:
The patent employs composite materials by creating a composite structure where SiOC is combined with silicon or silicon alloy phases. This composite material approach enables the system to exhibit both the cycle stability of SiOC and the high capacity of silicon-based components
3Quantity of substance
If fine silicon particles are used, then charge/discharge capacity is improved, but particle size reduction due to volume expansion and contraction limits practical application
Solution Approach 1:
The patent applies this principle by coating silicon particles with a flexible carbon-containing material that can accommodate volume changes. This allows the use of fine silicon particles for high capacity while the protective shell prevents excessive size reduction and maintains structural integrity during manufacturing and cycling
Solution Approach 2:
The patent uses beforehand cushioning by pre-forming a carbon-containing coating on silicon particles before battery assembly. This pre-established protective layer cushions against volume expansion and contraction during subsequent charge/discharge cycles, preventing particle degradation and maintaining manufacturability
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, efficient coulombic efficiency, and improved cycle life, allowing for the use of larger silicon particles and enabling a mass-production process while maintaining lithium ion conductivity and structural integrity.
Implementation Method 1
a silicon-based inorganic compound (a) composed of silicon (excluding zerovalent silicon), oxygen, and carbon... in which an equivalent constituent ratio indicating a chemical bonding state of silicon... is within the range of from 0.30 to 0.80
Implementation Method 2
maintaining lithium ion conductivity and structural integrity
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.