Amorphous Carbon Coated Silicon Anode for Li-Ion Batteries
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Solution Overview
Problem
Lithium ion batteries face issues with silicon negative electrode active materials due to significant volume expansion and contraction during charging and discharging, leading to poor cycle characteristics and increased internal resistance, as well as electrolyte decomposition, which affects battery stability.
Innovation Solution
A negative electrode active material with an amorphous carbon coating layer, derived from a specific resin, is applied to enhance adhesiveness and stability during volume changes, improve contact with conductive aids and current collectors, and suppress electrolyte decomposition, thereby achieving better cycle and rate characteristics and coulombic efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon is used as a negative electrode active material to achieve high theoretical capacity, then the lithium storage capacity is improved, but the volume expansion and contraction during charging and discharging causes the active material to break after repeated cycles
Solution Approach 1:
The patent applies the nesting principle by placing silicon particles inside a porous carbon matrix structure. The carbon matrix acts as a container that accommodates the silicon particles, allowing the silicon to expand and contract during lithium insertion/extraction cycles without breaking. This nested structure enables the high-capacity silicon to be protected while maintaining its electrochemical activity.
Solution Approach 2:
The patent employs a flexible porous carbon matrix that can accommodate the volume changes of silicon particles during charging and discharging. The carbon matrix acts as a flexible shell that deforms with the silicon particles, preventing structural breakdown and maintaining electrical conductivity throughout the cycling process.
2Reliability
If carbon coating is applied to silicon particles to enhance cycle characteristics, then the structural stability is improved, but the hardness and brittleness of silicon carbide reduces adhesiveness and increases internal resistance
Solution Approach 1:
The patent utilizes a porous carbon matrix instead of a dense carbon coating layer. The porous structure provides multiple benefits: it maintains flexibility to accommodate silicon volume changes, preserves electrical conductivity through the porous network, reduces internal resistance by avoiding the insulating effect of dense silicon carbide, and allows efficient lithium ion transport through the pores. The porous structure prevents the formation of a continuous insulating barrier while still providing structural support and adhesion.
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 amorphous carbon coating layer provides high adhesiveness and stability to the silicon particles, reducing internal resistance and electrolyte decomposition, resulting in improved cycle stability and coulombic efficiency, even under increased charge/discharge rates.
Implementation Method 1
the electrolyte solution near the surface of the active material decomposes during charging and discharging (particularly the initial charging and discharging) to deposit insoluble salts such as Li2O, Li2CO3, or LiF on the surface of the active material
Implementation Method 2
the silicon undergoes significant volume expansion and contraction (>300%) with the lithium intercalation and deintercalation
Data Source
AI summary
The present invention provides a negative electrode active material for lithium ion batteries which has high adhesiveness and followability to a negative electrode active material in volume expansion and contraction during charging and discharging, excellent contact and adhesiveness to a conductive aid, a binder, and a current collector, and a high suppressing effect on decomposition of an electrolyte solution. Due to these features, the negative electrode active material for lithium ion batteries is capable of achieving excellent cycle characteristics and rate characteristics and high coulombic efficiency. The present invention also provides a negative electrode for lithium ion secondary batteries and a lithium ion secondary battery each including the negative electrode active material for lithium ion batteries, and a method for producing a negative electrode active material for lithium ion batteries. Provided is a negative electrode active material for lithium ion batteries, including: a negative electrode active material; and a coating layer containing an amorphous carbon on a surface of the negative electrode active material, the amorphous carbon constituting the coating layer having a ratio of a peak derived from a sp2 component to a peak derived from a sp3 component of 1 or higher as determined by 13C solid-state NMR, and a ratio of a peak derived from aromatic carbon having a bond with a hydroxy group to the peak derived from the sp2 component of 0.2 or lower.