LiBOB SEI Film Composition for Battery Capacity and Resistance
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Solution Overview
Problem
Nonaqueous electrolyte secondary cells face challenges in maintaining high performance due to irreversible decomposition of the electrolytic solution during initial charge, leading to decreased cell capacity and increased resistance, particularly when forming the SEI film using LiBOB as a film forming agent.
Innovation Solution
The formation of a nonaqueous electrolyte secondary cell with a negative electrode SEI film containing a LiBOB skeleton and a fluorosulfonic acid skeleton, and a positive electrode SEI film with a phosphoric acid skeleton, where the component ratios and specific surface area of the negative electrode active material are optimized to balance cell capacity and resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LiBOB is used as a film forming agent to form SEI film on the negative electrode, then the negative electrode is stabilized and subsequent decomposition of the electrolytic solution is suppressed, but the decomposition of the electrolytic solution causes a decrease in cell capacity
Solution Approach 1:
The patent applies preliminary action by adding LiBOB as a film forming agent that decomposes during initial charge to form an SEI film on the negative electrode surface before normal operation begins. This pre-formed protective film prevents subsequent electrolytic solution decomposition, stabilizing the negative electrode while minimizing capacity loss from irreversible reactions.
2Reliability
If the SEI film is formed by decomposition of the electrolytic solution, then the negative electrode is stabilized, but it causes a decrease in cell capacity due to irreversible reaction
Solution Approach 1:
The invention uses preliminary action by introducing LiBOB as a dedicated film forming agent that undergoes controlled decomposition during initial charge to create the protective SEI film. This approach shifts the irreversible decomposition reaction to a predetermined stage (initial charge) rather than during normal operation, thereby stabilizing the negative electrode while preserving cell capacity for subsequent cycles.
3Reliability
If LiBOB is used as a film forming agent to improve cell performance, then the negative electrode stability is enhanced, but the cell resistance increases due to the SEI film formation
Solution Approach 1:
The patent applies parameter changes by optimizing the concentration of LiBOB in the electrolytic solution and controlling the initial charge conditions to form an SEI film with appropriate thickness and composition. By adjusting these parameters, the film provides sufficient protection for negative electrode stability while maintaining adequate ionic conductivity to minimize resistance increase.
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 effectively suppresses the deterioration of cell capacity and reduces reaction resistance, enabling the cell to be used as a high-output power source for vehicles by maintaining a suitable balance between Li ion movement speed and film component amounts.
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
nonaqueous electrolyte secondary cells such as lithium ion secondary cells have been suitably used as so-called portable power sources
Data Source
AI summary
According to the present invention, 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 (1) represented by 4≤IB/IS≤10 and a formula (2) represented by 5 μmol/m2≤IP≤15 μmol/m2 are satisfied. Furthermore, the BET specific surface area of the negative electrode active material is 3.5 m2/g or more and 5.0 m2/g or less, and the component amount IB of the LiBOB skeleton is 4.3 μmol/m2 or more.