Secondary Battery Electrolyte Ratios for Stable SEI at High Temperature
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Solution Overview
Problem
Secondary batteries face challenges in achieving improved cycle performance and high-temperature storage performance due to instability of the solid electrolyte interface film (SEI) formed by boron-containing lithium salts, leading to decomposition and reduced structural stability of the negative electrode active material.
Innovation Solution
The use of a boron-containing lithium salt in the electrolytic solution, with specific mass ratios and additives, forms a stable SEI film on the negative electrode active material, enhancing film-forming stability and conductivity, thereby improving cycle and high-temperature storage performance by controlling the discharge capacity and mass percentage of the boron-containing lithium salt within specific ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If boron-containing lithium salt is used to form SEI film on negative electrode, then cycle performance is improved, but high-temperature storage performance deteriorates due to film instability and decomposition
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte by introducing a boron-containing lithium salt with specific molecular structure (LiB(OX)2 where X is F or Cl) and controlling its concentration within 0.01-5% by mass. This parameter optimization enables the formation of a stable SEI film that improves cycle performance while maintaining high-temperature storage performance, resolving the contradiction between the two performance aspects.
2Reliability
If mass percentage of boron-containing lithium salt is increased to improve film-forming stability, then cycle performance improves, but electrolyte decomposition increases at high temperature
Solution Approach 1:
The patent optimizes the concentration parameter of boron-containing lithium salt to a specific range (0.01-5% by mass) and controls the mass ratio of electrolyte to discharge capacity (B/A) within 1-5. These parameter changes ensure sufficient film-forming stability for improved cycle performance while preventing excessive electrolyte decomposition at high temperatures, thus resolving the contradiction.
Solution Approach 2:
The patent creates a composite electrolyte system combining boron-containing lithium salt (LiB(OX)2) with conventional lithium salts (such as LiPF6, LiBF4) in specific proportions. This composite approach leverages the film-forming capability of boron-containing salts while the conventional salts maintain electrolyte conductivity and stability, reducing decomposition at high temperatures while improving cycle performance.
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 results in improved structural stability and capacity retention of the secondary battery, ensuring effective protection of the negative electrode active material and enhancing both cycle and high-temperature storage performance.
Implementation Method 1
the boron-containing lithium salt is configured to form a solid electrolyte interface film on the surface of the negative electrode active material
Implementation Method 2
the electrolytic solution comprises a boron-containing lithium salt
Data Source
AI summary
A secondary battery, a battery module, a battery pack, and an electrical device are disclosed. The secondary battery includes a positive electrode plate, a negative electrode plate and an electrolytic solution, the negative electrode plate including a negative electrode film layer containing a negative electrode active material; and the electrolytic solution including a boron-containing lithium salt, the boron-containing lithium salt being configured to form a solid electrolyte interface film on the surface of the negative electrode active material, wherein a discharge capacity of the secondary battery is denoted as A in Ah, a mass of the electrolytic solution is denoted as B in g, a mass percentage of the boron-containing lithium salt relative to a total mass of the electrolytic solution is denoted as C %; and the secondary battery satisfies: 1≤B/A≤5, 5×10−6≤B×C %/A≤0.25.