Wound Battery Electrolyte Ratio for Large-Cell Cycle Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Non-aqueous electrolyte secondary batteries with wide electrode assemblies experience nonuniform salt concentrations during high-rate cycles, leading to increased positive electrode potential and capacity degradation due to SO3F− adsorption and inadequate LiF film formation, especially in large cell sizes.
Innovation Solution
A non-aqueous electrolyte secondary battery design featuring a wound-type electrode assembly with a pressure of 0.5 MPa applied in the electrode plate stacking direction, using an electrolyte solution with a specific ratio of LiPF6 to LiFSO3 (A/B ratio from 5 to 12) to ensure sufficient LiF film formation and prevent transition metal elution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If an electrolyte solution including LiFSO3 is used, then the output resistance is reduced, but the LiF film formation on the positive electrode is inhibited and transition metal elution occurs
Solution Approach 1:
The patent changes the concentration parameters of the electrolyte salts LiPF6 and LiBF4 to achieve optimal LiF film formation. Specifically, the total concentration of LiPF6 and LiBF4 is controlled at 0.5 to 2.0 mol/L, with LiPF6 at 0.1 to 1.5 mol/L and LiBF4 at 0.1 to 1.0 mol/L. This parameter optimization ensures sufficient LiF film formation while maintaining low output resistance, resolving the contradiction between power and reliability.
2Quantity of substance
If the cell size is large with wide electrode assembly, then the capacity is increased, but the salt concentrations become nonuniform during high-rate cycles and capacity degradation occurs
Solution Approach 1:
The patent optimizes the electrolyte salt concentrations to ensure uniform salt distribution in large cells. The total concentration of LiPF6 and LiBF4 is controlled at 0.5 to 2.0 mol/L, with specific ranges for each salt. This parameter control maintains stable ionic conductivity and uniform salt concentrations during high-rate cycles, preventing capacity degradation while preserving high capacity.
Solution Approach 2:
The patent uses a composite electrolyte system combining LiPF6 and LiBF4 salts in specific ratios. This composite approach leverages the complementary properties of both salts: LiPF6 provides good ionic conductivity while LiBF4 enhances film stability. The synergistic effect ensures uniform salt distribution and stable performance in large-format cells during high-rate cycling.
3Strength
If pressure of 0.5 MPa or more is applied to the electrode assembly, then the contact between electrodes is improved, but the salt concentration nonuniformity is exacerbated during high-rate cycles
Solution Approach 1:
The patent optimizes the electrolyte composition to counterbalance the effects of applied pressure. By controlling the total salt concentration at 0.5 to 2.0 mol/L and maintaining specific individual concentrations of LiPF6 (0.1 to 1.5 mol/L) and LiBF4 (0.1 to 1.0 mol/L), the electrolyte maintains sufficient ionic conductivity and uniform distribution even under 0.5 MPa or higher pressure, ensuring stable 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
The solution results in reduced output resistance and improved cycling performance, with capacity retention of 90% or more, by maintaining the electric potential within safe limits and preventing metal deposition on the negative electrode.
Implementation Method 1
formation of a film of LiF derived from electrolyte salts tends to be inhibited
Implementation Method 2
SO3F− tends to be adsorbed on the surface of the positive electrode active material
Implementation Method 3
the electrolyte solution includes an electrolyte salt and LiFSO3
Data Source
AI summary
The present disclosure relates to a non-aqueous electrolyte secondary battery comprising a wound-type electrode assembly and an electrolyte solution. In the non-aqueous electrolyte secondary battery according to the present disclosure, a dimension of at least one of a positive electrode active material layer and a negative electrode active material layer in a direction of an axis of winding of the electrode assembly is 150 mm or more, the electrolyte solution includes an electrolyte salt and LiFSO3, the electrolyte salt includes at least one of LiPF6 and LiBF4, a ratio of a total concentration A (mol/L) of LiPF6 and LiBF4 to a concentration B (mol/L) of LiFSO3 in the electrolyte solution, which is expressed as an A/B ratio, is from 5 to 12, and a pressure of 0.5 MPa or more is applied to the electrode assembly in an electrode plate stacking direction.