Lithium Battery Electrolyte Additives for Stable CEI and SEI
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Solution Overview
Problem
Lithium secondary batteries face degradation due to increased interface reactivity with the electrolyte, leading to rapid degradation of electrochemical performance, especially when using high-capacity cathode active materials like NCM-based oxides.
Innovation Solution
Incorporating vinylene carbonate (VC) and 4-(allyloxy)phenyl fluoro sulfate as additives in the electrolyte solution, which form stable cathode electrolyte interphase (CEI) and solid electrolyte interphase (SEI) on the cathode and anode, respectively, thereby enhancing the electrochemical properties of the battery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high-capacity cathode active materials like NCM-based oxides are used to increase battery capacity, then the energy density is improved, but the interface reactivity with the electrolyte increases leading to rapid degradation of electrochemical performance
Solution Approach 1:
The patent applies preliminary action by introducing additives (vinylene carbonate and fluoroethylene carbonate) into the electrolyte before battery operation begins. These additives proactively form protective interphase films (CEI on cathode and SEI on anode) during initial cycles, preventing direct contact between the high-reactivity NCM cathode material and the bulk electrolyte. This preliminary protective layer formation resolves the contradiction by enabling high capacity utilization while preventing subsequent degradation.
Solution Approach 2:
The patent uses interphase films formed by additives as intermediary layers between the NCM cathode and electrolyte. These intermediary films (particularly the CEI layer) act as mediators that allow lithium ion transport while blocking harmful direct reactions between the high-capacity cathode material and electrolyte. This resolves the technical contradiction by maintaining high capacity benefits while eliminating degradation pathways through the intermediary protective layer.
2Quantity of substance
If the nickel content in NCM-based oxide is increased to increase cathode capacity, then the energy density is improved, but the degradation rate increases due to increased interface reactivity with the electrolyte
Solution Approach 1:
The patent extracts the harmful interface reaction products by using additives that preferentially react to form stable interphase films. The vinylene carbonate and fluoroethylene carbonate additives are extracted into the interphase layer, forming CEI and SEI films that remove the reactive interface between high-nickel NCM cathode and electrolyte. This extraction of harmful reactive components resolves the contradiction by separating the high-capacity cathode material from its harmful interactions while maintaining electrochemical functionality.
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 use of these additives significantly improves the lifespan and output characteristics of lithium secondary batteries by forming stable interphases that reduce degradation and enhance lithium ion conductivity.
Implementation Method 1
the additive induces the formation of SEI on the surface of the anode
Implementation Method 2
a thin film called solid electrolyte interphase (SEI) is formed on the anode
Implementation Method 3
SEI is a membrane that can pass lithium ions but not electrons
Implementation Method 4
SEI is a membrane that can pass lithium ions but not electrons
Implementation Method 5
the SEI suppresses the direct reaction of the electrolyte and the anode
Data Source
AI summary
An additive for an electrolyte solution improves the electrochemical properties of a lithium secondary battery.