Polymer-Coated Metal-Graphite Composite for Battery Capacity
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Solution Overview
Problem
Lithium metal batteries face issues with short circuits, explosions due to dendrite formation, and limited capacity from traditional carbon-based negative electrodes, while metal composite active materials suffer from volume expansion and degradation, leading to reduced cycle life and high rate discharge characteristics.
Innovation Solution
A metal composite negative electrode active material is developed, featuring a graphite core particle with metal particles coated by a polymer film, which suppresses volume expansion and secures the metal particles to the graphite core, enhancing cycle life and high rate discharge capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If metal particles (Si, Sn, Ge, etc.) are used as negative electrode active materials to increase capacity, then the battery capacity increases, but the volume expansion of metal particles reaches 300-400% during lithium ion intercalation, causing electrode degradation and reduced cycle life
Solution Approach 1:
Metal particles are embedded within graphite core particles, creating a core-shell structure where the graphite shell contains the metal core. This nested structure allows the metal particles to expand and contract during lithium ion intercalation/deintercalation while being constrained by the graphite shell, preventing electrode degradation and maintaining cycle life while utilizing the high capacity of metal particles.
Solution Approach 2:
The invention uses composite materials combining metal particles with graphite shell and polymer coating. The composite structure integrates the high capacity advantage of metal particles with the structural stability of graphite and the protective properties of polymer, resolving the contradiction between capacity and cycle life.
2Quantity of substance
If inorganic particles are used to increase capacity, then the theoretical capacity exceeds that of carbon materials, but the repeated charge-discharge cycles cause particle detachment and side reactions with electrolyte, reducing high rate discharge characteristics
Solution Approach 1:
A polymer film is coated on the surface of the graphite core particle and metal particles. This flexible polymer shell protects the metal particles from direct contact with electrolyte, preventing side reactions and particle detachment during high rate discharge cycles, thereby maintaining reliability and high rate discharge characteristics while utilizing high theoretical capacity.
Solution Approach 2:
The polymer coating acts as an intermediary layer between the metal particles and electrolyte. It mediates the interaction by allowing lithium ion transport while preventing direct contact between metal particles and electrolyte, thus preventing side reactions and maintaining high rate discharge characteristics.
3Quantity of substance
If metal composite negative electrode active materials are used to achieve high capacity, then the capacity exceeds traditional carbon limits, but volume expansion causes negative electrode active material degradation
Solution Approach 1:
Metal particles are nested within graphite core particles with polymer coating, creating a protective nested structure. The graphite shell and polymer coating constrain the metal particles during volume expansion, preventing electrode degradation while maintaining high capacity.
Solution Approach 2:
The polymer coating is applied beforehand to the graphite core particle and metal particles, providing a cushioning protective layer that absorbs and distributes the stress from volume expansion during lithium ion intercalation, preventing electrode degradation while maintaining high 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-coated metal composite negative electrode active material improves cycle life and high rate discharge characteristics by preventing electrolyte reactions and maintaining the integrity of metal particles, resulting in higher capacity and energy density for lithium secondary batteries.
Implementation Method 1
a metal composite negative electrode active material having improved cycle life and high rate discharge characteristics by suppressing volume expansion of the metal particles
Implementation Method 2
at least one metal particle located on the graphite core particle, and a film coating the graphite core particle and the metal particle(s)
Implementation Method 3
when the particles are exposed to the intercalation of lithium ions
Implementation Method 4
As lithium ions are deintercalated during the discharging cycle
Data Source
AI summary
A lithium secondary battery includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, a separator separating the positive electrode from the negative electrode, and an electrolyte. The negative electrode active material includes a graphite core particle, at least one metal particle located on the graphite core particle, and a polymer film coating the graphite core particle and the at least one metal particle. The polymer includes a polyimide- or polyacrylate-based polymer.