Negative Electrode Porosity and Graphite Orientation for Lithium Battery
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Solution Overview
Problem
Lithium rechargeable batteries face issues with volume change and stress due to active material particle expansion during charge and discharge, leading to suboptimal cell characteristics and safety concerns with graphite as a negative active material.
Innovation Solution
A negative electrode with a metal-based active material and sheet-shaped graphite, optimized porosity, and oriented (002) planes to reduce stress and improve conductivity, comprising 20-80% porosity and 5-80% sheet-shaped graphite by weight, with the graphite having an average particle diameter of 1-20 μm and being oriented either in the same direction or vertically to the current collector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If graphite is used as a negative active material, then discharge voltage and energy density are improved, but safety risks (explosion or combustion) increase due to reaction with organic electrolyte at high discharge voltage
Solution Approach 1:
A coating layer comprising at least one of an oxide coating and a nitride coating is formed on the graphite particles. This coating layer acts as an intermediary barrier between the graphite and the organic electrolyte, preventing direct reaction while allowing lithium ion intercalation and deintercalation, thus maintaining safety while preserving energy density benefits
2Use of energy by moving object
If graphite is used as a negative active material, then discharge voltage is improved, but cycle life is reduced due to volume change and stress during charge and discharge
Solution Approach 1:
The negative electrode is designed with a porous structure comprising graphite particles and a binder, where the porous network provides expansion space for graphite during lithium intercalation. This porous architecture accommodates volume change without generating excessive stress, thereby maintaining structural integrity over multiple cycles while preserving the high discharge voltage characteristics of graphite
Solution Approach 2:
The negative electrode uses a composite structure combining graphite particles with a binder material. This composite approach allows the graphite to provide high discharge voltage while the binder matrix accommodates volume expansion and maintains electrical connectivity, thereby extending cycle life without sacrificing voltage performance
3Object-affected harmful factors
If oxide negative electrode materials are used, then safety is improved by reducing reaction with organic electrolyte, but battery performance is insufficient compared to graphite
Solution Approach 1:
The negative electrode employs a composite structure where graphite particles (providing high performance) are coated with oxide or nitride layers (providing safety). This composite material approach allows the internal graphite core to deliver high discharge voltage and energy density while the external oxide/nitride coating prevents harmful reactions with the organic electrolyte, thus achieving both safety and performance
4Stability of the object's composition
If metal-based negative active materials are used, then volume change during charge and discharge is reduced, but electrode resistance increases
Solution Approach 1:
A conductive coating layer comprising at least one of an oxide coating and a nitride coating is formed on the metal-based negative active material particles. This coating layer acts as a conductive intermediary that maintains low electrode resistance while allowing the underlying metal-based material to provide volume stability during charge and discharge cycles
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 configuration effectively inhibits volume expansion, reduces electrode resistance, and enhances battery performance by improving energy density and cycle life while minimizing the risk of explosion or combustion.
Implementation Method 1
graphite has a low discharge potential of −0.2V compared to lithium. A battery using graphite as a negative active material has a high average discharge potential of 3.6V and an excellent energy density. Furthermore, graphite guarantees a better cycle life for a battery due to its outstanding reversibility.
Implementation Method 2
The negative active material layer includes a metal-based negative active material and sheet-shaped graphite and has porosity of 20 to 80 volume %. pores of the negative active material layer having a pore diameter of 1 μm or less constitute 30 to 70 volume % based on the total volume of the negative active material layer.
Implementation Method 3
The (002) planes of the sheet-shaped graphite may be oriented in the same direction. The (002) planes of the sheet-shaped graphite may be oriented in a vertical direction with respect to the current collector.
Data Source
AI summary
The negative electrode for a rechargeable lithium battery includes a current collector and a negative active material layer disposed on the current collector. The negative active material layer includes a metal-based negative active material and sheet-shaped graphite and has porosity of 20 to 80 volume %. The negative electrode for a rechargeable lithium battery can improve cell characteristics by inhibiting volume change and stress due to active material particle bombardment during charge and discharge, and by decreasing electrode resistance.