Low Crystalline Carbon Coated Graphite for Battery Cycle Stability
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Solution Overview
Problem
Non-aqueous electrolyte secondary batteries using propylene carbonate as a solvent face challenges with graphite negative electrodes due to reaction and decomposition, leading to reduced charge/discharge efficiency and cycle performance, especially under high temperature conditions, when low crystalline carbon coatings peel off and expose the graphite.
Innovation Solution
Employing low crystalline carbon coated graphite with a specific intensity ratio and a mixed solvent of propylene carbonate and chain carbonate, along with a lithium salt having an oxalate complex anion, to prevent peeling and enhance cycle performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If propylene carbonate is used as the non-aqueous solvent to improve power performance under low temperature conditions, then low temperature power performance is improved, but propylene carbonate reacts with graphite and decomposes, leading to reduced charge/discharge efficiency and cycle performance
Solution Approach 1:
A silane-based coating layer is applied to the graphite surface to act as an intermediary barrier. This coating prevents direct contact and reaction between propylene carbonate and graphite, while still allowing lithium ion insertion and extraction. The coating includes specific functional groups that provide both protection and ion conductivity, resolving the contradiction between maintaining power performance and preventing decomposition.
Solution Approach 2:
The surface properties of graphite are modified by applying a silane-based coating that changes the chemical and physical parameters of the surface. This coating alters the surface energy, porosity, and chemical reactivity to prevent propylene carbonate decomposition while maintaining lithium ion transport properties, thus improving charge/discharge efficiency without sacrificing power performance.
2Reliability
If low crystalline carbon is coated on graphite surface to prevent propylene carbonate reaction, then charge/discharge efficiency is improved, but the coating peels off during charge/discharge cycling, leading to reduced cycle performance
Solution Approach 1:
A composite silane-based coating system is employed that combines multiple functional components: silane backbone structure for adhesion, functional groups for chemical bonding to graphite, and porous structure for ion transport. This composite material provides both strong attachment to prevent peeling and appropriate properties for lithium ion insertion/extraction, ensuring excellent cycle performance.
Solution Approach 2:
The coating is designed with spatially varying properties: the inner layer provides strong adhesion to graphite surface, the intermediate layer provides chemical stability against propylene carbonate, and the outer porous layer facilitates lithium ion transport. This local differentiation of material properties ensures both coating stability and electrochemical performance over extended cycling.
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 solution achieves stable charge/discharge cycle performance and high energy density by preventing peeling of the low crystalline carbon coating and improving electrolyte perviousness, thus maintaining battery capacity under repeated cycling and high temperature conditions.
Implementation Method 1
low crystalline carbon coated graphite in which at least part of the surface of graphite is coated with a low crystalline carbon material
Implementation Method 2
non-aqueous electrolyte comprising an electrolyte dissolved in a non-aqueous solvent
Implementation Method 3
lithium ion is moved between their positive electrodes and negative electrodes to perform charging and discharging
Implementation Method 4
reaction between propylene carbonate and the graphite of the negative electrode active material is restricted
Data Source
AI summary
A non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte comprising an electrolyte dissolved in a non-aqueous solvent. The negative electrode uses a low crystalline carbon coated graphite in which at least part of the surface of graphite is coated with a low crystalline carbon material having lower crystallinity than that of graphite as a negative electrode active material, and the non-aqueous electrolyte comprises a lithium salt which has oxalate complex as an anion, in addition to a mixed solvent of propylene carbonate and chain carbonate as a non-aqueous solvent.