Alkoxy Phosphine Additive for Lithium Battery SEI Stability
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Solution Overview
Problem
Lithium secondary batteries face issues with electrolyte decomposition, leading to gas generation, poor high-temperature performance, and safety concerns due to the reaction of LiPF6 with solvents, and high-Ni-content cathode active materials have poor lifetime characteristics due to weak surface structures.
Innovation Solution
A lithium secondary battery design incorporating a cathode active material represented by Formula 1 (Li x Ni y M 1-y O 2-z) and an electrolyte with a compound represented by Formula 2, which includes -ORn groups that suppress solvent decomposition, reduce gas generation, and form a stable SEI film, improving cycle lifetime and high-temperature stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LiPF6 is used as a lithium salt in the electrolyte, then high ionic conductivity is achieved, but solvent decomposition occurs leading to gas generation and electrolyte depletion
Solution Approach 1:
The patent introduces a fluorinated cyclic carbonate compound as an intermediary substance in the electrolyte. This compound acts as a mediator between LiPF6 and the solvent, preferentially reacting with LiPF6 to form a stable protective film on the electrode surface. This intermediary layer prevents direct contact between LiPF6 and the bulk solvent, thereby suppressing solvent decomposition and gas generation while maintaining the ionic conductivity benefits of LiPF6.
Solution Approach 2:
The fluorinated cyclic carbonate compound performs preliminary action by forming a stable protective film on the electrode surface before the solvent can decompose. This pre-formed film acts as a barrier that prevents subsequent solvent decomposition and gas generation during battery operation, thereby resolving the contradiction between maintaining ionic conductivity and preventing harmful gas generation.
2Quantity of substance
If high-Ni-content cathode active materials are used, then higher battery capacity is achieved, but lifetime characteristics deteriorate due to weak surface structure
Solution Approach 1:
The patent applies local quality by modifying only the surface region of the high-Ni-content cathode active material through the formation of a protective film. The bulk composition maintains high Ni content for high capacity, while the surface region acquires different chemical properties through the fluorinated cyclic carbonate compound. This creates a gradient structure where the surface has enhanced stability and the interior maintains high capacity, thereby resolving the contradiction between high capacity and long lifetime.
3Speed
If the electrolyte operates at high temperature, then charging speed is improved, but side reactions increase leading to electrolyte depletion and safety issues
Solution Approach 1:
The patent converts the harmful effect of high temperature into a beneficial outcome. The fluorinated cyclic carbonate compound is specifically designed to be thermally stable and preferentially reacts at elevated temperatures to form a robust protective film. This film, formed under high-temperature conditions, subsequently prevents further side reactions and electrolyte depletion, thereby allowing high-temperature fast charging while maintaining safety and preventing electrolyte depletion.
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 battery exhibits enhanced cycle lifetime and high-temperature stability, with the -ORn groups in the electrolyte additive reducing resistance increase rates and preventing swelling, while forming a protective film on the anode and cathode, thereby improving overall battery performance.
Implementation Method 1
the -ORn groups in the electrolyte additive reducing resistance increase rates and preventing swelling, while forming a protective film on the anode and cathode
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
A lithium secondary battery includes: a cathode, an anode; and an electrolyte between the cathode and the anode, wherein the cathode includes a cathode active material represented by Formula 1 below, and the electrolyte includes a lithium salt, a nonaqueous solvent, and a compound represented by Formula 2, where x, y, z, M, A, L1, a1, and R1 to R4 are defined as described in the disclosure. Formula 1 LixNiyM1-yO2-zAz