Polymer-Coated Metallic Anode for Lithium Battery Volume Expansion
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Solution Overview
Problem
Lithium rechargeable batteries face challenges with the low cycle-life characteristics and volume expansion of metallic negative active materials during lithium ion intercalation and deintercalation, leading to degraded conductivity and potential electrolyte leakage.
Innovation Solution
A negative active material is developed by coating a high-strength polymer with a tensile strength of at least 40 MPa on metallic active material particles, such as lithium vanadium-based oxides or tin oxides, to suppress volume change and improve cycle-life characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If metallic active material is used for high capacity, then energy density is improved, but volume expansion occurs during lithium ion intercalation and deintercalation
Solution Approach 1:
A polymer coating layer is applied on the surface of metallic active material particles to form a flexible protective shell. This shell accommodates volume changes during lithium ion intercalation and deintercalation, preventing cracking and maintaining structural integrity while allowing the metallic core to expand and contract.
Solution Approach 2:
The invention creates a composite structure combining metallic active material particles with a polymer coating layer. The metallic core provides high capacity while the polymer shell provides mechanical stability and volume control, achieving a synergistic effect that resolves the contradiction between high capacity and volume stability.
2Quantity of substance
If metallic active material is used for high capacity, then energy density is improved, but cycle-life characteristics are degraded
Solution Approach 1:
The polymer coating layer acts as a protective shell that maintains structural integrity during repeated charge-discharge cycles. It prevents particle cracking and degradation, ensuring long-term reliability while preserving the high capacity of the metallic core material.
Solution Approach 2:
The polymer coating is applied in advance to cushion and absorb mechanical stresses during volume expansion and contraction. This pre-protective layer prevents damage accumulation that would otherwise lead to premature failure during cycling.
3Quantity of substance
If metallic active material is used for high capacity, then energy density is improved, but conductivity is reduced due to volume expansion
Solution Approach 1:
The polymer coating maintains continuous electro-conductive paths by accommodating volume changes without cracking. This flexible shell ensures stable electrical contact between particles during cycling, preserving conductivity while allowing the metallic core to maintain its high capacity.
4Quantity of substance
If graphite is used as negative active material for low discharge potential, then energy density is improved, but reaction with organic electrolyte at high discharge voltage can lead to combustion or explosion
Solution Approach 1:
The polymer coating serves as an intermediary layer between the metallic active material and the organic electrolyte. It prevents direct harmful reactions while allowing beneficial lithium ion transport, thus eliminating the safety issues associated with graphite-electrolyte reactions while maintaining high energy density.
5Object-affected harmful factors
If oxide negative active material is used to avoid electrolyte reaction, then safety is improved, but initial irreversible capacity is high
Solution Approach 1:
The invention combines metallic active material with polymer coating to create a composite that achieves both low irreversible capacity (inherent advantage of metallic materials) and electrolyte stability (provided by the polymer shell). This avoids the need to use oxide materials that inherently suffer from high initial irreversible capacity.
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 polymer coating effectively reduces volume expansion, enhances electroconductivity, and maintains electro-conductive paths within the electrode, thereby improving battery cycle-life and preventing deformation.
Implementation Method 1
coating a high-strength polymer with a tensile strength of at least 40 MPa on metallic active material particles, such as lithium vanadium-based oxides or tin oxides, to suppress volume change
Implementation Method 2
maintains electro-conductive paths within the electrode, thereby improving battery cycle-life and preventing deformation
Data Source
AI summary
A negative active material of a negative electrode of a rechargeable lithium battery, the negative active material including a metallic active material core and a polymer, having a tensile strength of at least 40 MPa, coated on particles of the metallic active material. The polymer controls the volumetric expansion of the negative active material and enhances the cycle-life characteristics of the battery.