Lithium Secondary Battery Electrolyte Additive for Iron Ion Capture
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Solution Overview
Problem
Lithium transition metal phosphates with an olivine structure face issues of low electrical conductivity and iron (Fe) ion exsolution into the electrolyte during charging and discharging, leading to increased internal resistance and degraded battery performance.
Innovation Solution
Incorporating an electrolyte additive with a specific molecular weight and bimodal molecular weight distribution, along with a cyano group-containing unit, to coordinate bond and capture iron ions, thereby inhibiting their exsolution and reducing internal resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LiMPO4 with an olivine structure is used as a positive electrode active material, then high-temperature stability and cost-effectiveness are improved, but electrical conductivity is reduced and iron ions exsolve into the electrolyte
Solution Approach 1:
A coating layer comprising at least one of a metal oxide, a metal hydroxide, or a metal carbonate is applied to the surface of the LiMPO4 positive electrode active material. This coating layer acts as an intermediary that prevents direct contact between the iron ions and the electrolyte, thereby inhibiting iron ion exsolution while maintaining the high-temperature stability and cost-effectiveness of the LiMPO4 material.
2Reliability
If a coating layer is formed on the positive electrode active material surface, then iron ion exsolution is inhibited, but manufacturing process complexity increases
Solution Approach 1:
The coating layer is formed on the surface of the positive electrode active material before the electrode assembly is manufactured. This preliminary action ensures that the coating is already in place during battery assembly, eliminating the need for additional doping processes later and simplifying the overall manufacturing process while effectively inhibiting iron ion exsolution.
3Quantity of substance
If transition metal ions are used in the positive electrode, then battery capacity is improved, but metal ions exsolve into the electrolyte causing side reactions
Solution Approach 1:
The coating layer, comprising metal oxide, metal hydroxide, or metal carbonate, is designed to react with exsolved iron ions to form stable compounds. This converts the harmful effect of iron ion exsolution into a beneficial outcome by trapping the iron ions in a stable form, preventing them from causing side reactions in the electrolyte while maintaining the high capacity benefits of using transition metal ions.
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 effectively prevents iron ion exsolution, maintaining battery performance and safety by minimizing resistance increases and side reactions, especially under high-temperature conditions.
Implementation Method 1
Incorporating an electrolyte additive with a specific molecular weight and bimodal molecular weight distribution, along with a cyano group-containing unit, to coordinate bond and capture iron ions
Data Source
AI summary
A lithium secondary battery has excellent economic feasibility and safety because an iron phosphate of Formula 2 having an olivine structure is included as a positive electrode active material, and also has advantages of excellent battery performance and lifespan because an electrolyte additive of Formula 1 having a specific molecular weight is included in an electrolyte to improve an increase in internal resistance of the battery during charging and discharging and effectively prevent iron ions from being exsolved from the positive electrode active material,wherein R1 to R5, p, q, r, m and n are described herein.