LiBOB Fluorosulfonic Acid SEI Film Ratio for Battery Resistance
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Solution Overview
Problem
Nonaqueous electrolyte secondary cells face a trade-off between preventing capacity decrease and maintaining low cell resistance due to the formation of the SEI film by LiBOB, where excessive LiBOB can slow down Li ion movement and insufficient LiBOB can lead to electrolyte decomposition, and transition metal elution from the positive electrode active material increases reaction resistance.
Innovation Solution
Forming a negative electrode SEI film with a LiBOB skeleton and fluorosulfonic acid skeleton in a specific ratio (4≤IB/IS≤10) and a positive electrode SEI film with a phosphoric acid skeleton in a controlled amount (5 μmol/m2≤IP≤15 μmol/m2) to balance capacity retention and ion mobility, while preventing transition metal elution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LiBOB is added as a film forming agent to form SEI film on the negative electrode, then electrolyte decomposition is suppressed and cell capacity is maintained, but cell resistance increases due to slowed Li ion movement
Solution Approach 1:
The patent combines LiBOB with fluorosulfonic acid and a salt having P-F bond to create a composite electrolyte system. This composite approach forms a composite SEI film on the negative electrode that integrates the protective capacity-retaining properties of LiBOB with the ion-conducting benefits of fluorosulfonic acid derivatives, thereby maintaining cell capacity while reducing the harmful resistance increase
Solution Approach 2:
The patent modifies the chemical composition parameters of the electrolyte by introducing fluorosulfonic acid and P-F bond containing salts in specific amounts. This parameter change alters the SEI film formation process and composition, creating a film that allows faster Li ion transport while maintaining the protective function against electrolyte decomposition
2Reliability
If excessive LiBOB is used to form SEI film, then electrolyte decomposition is further suppressed, but Li ion movement speed decreases and cell resistance increases
Solution Approach 1:
The patent optimizes the concentration parameter of LiBOB in the electrolyte and introduces fluorosulfonic acid as a modifying agent. This parameter adjustment prevents excessive LiBOB accumulation in the SEI film, maintaining electrolyte stability while preserving Li ion mobility through the balanced composition
3Object-generated harmful factors
If SEI film is formed on the positive electrode to prevent transition metal elution, then reaction resistance is reduced, but cell capacity decreases due to electrolyte decomposition
Solution Approach 1:
The patent introduces fluorosulfonic acid and P-F bond containing salts as intermediary substances that mediate the SEI film formation process on the positive electrode. These intermediaries enable the formation of a protective film that prevents transition metal elution and reduces reaction resistance, while their presence in the electrolyte composition prevents excessive electrolyte decomposition, thereby preserving cell 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
This approach enhances cell performance by maintaining high capacity and low resistance, making the cells suitable for high-output power sources, such as vehicles, by optimizing the SEI film composition and structure.
Implementation Method 1
a part of the nonaqueous electrolytic solution (hereinafter also simply referred to as 'electrolytic solution') is decomposed at the time of initial charge, and a coating film called a solid electrolyte interface (SEI) film may be formed on the surface of the negative electrode active material
Implementation Method 2
When this SEI film is formed, the negative electrode is stabilized, so that subsequent decomposition of the electrolytic solution is suppressed
Implementation Method 3
a nonaqueous electrolyte secondary cell including a positive electrode, a negative electrode, and a nonaqueous electrolytic solution
Data Source
AI summary
According to the present disclosure, there is provided a technique making it possible to improve suitably the performance of a nonaqueous electrolyte secondary cell in which a SEI film is formed on the surface of a negative electrode active material. The nonaqueous electrolyte secondary cell disclosed herein includes a positive electrode 10, a negative electrode 20, and a nonaqueous electrolytic solution, wherein a negative electrode SEI film 29 including at least a LiBOB skeleton and a fluorosulfonic acid skeleton is formed on the surface of a negative electrode active material 28, and a positive electrode SEI film 19 including at least a phosphoric acid skeleton is formed on the surface of a positive electrode active material 18. Where the component amount of the LiBOB skeleton in the negative electrode SEI film 29 is denoted by IB, the component amount of the fluorosulfonic acid skeleton in the negative electrode SEI film 29 is denoted by IS, and the component amount of the phosphoric acid skeleton in the positive electrode SEI film 19 is denoted by IP, a formula of 4≤IB/IS≤10 and a formula of 5 μmol/m2≤IP≤15 μmol/m2 are satisfied.