Multi-Lithium Salt Electrolyte for High-Rate Capacity Retention
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Solution Overview
Problem
Conventional lithium-ion batteries face challenges in meeting high power demands due to increased internal resistance and voltage drop at high discharge rates, especially in applications requiring high voltage and current output, such as power tools and drones, where capacity retention is compromised.
Innovation Solution
A lithium-based battery electrolyte formulation incorporating at least two lithium salts, specifically lithium hexafluorophosphate and another salt like lithium bis(trifluoromethanesulfonyl)imide, with a molar ratio ranging from 15:1 to 1:6 and concentrations of 1.5M to 5M, along with a lithium salt additive, enhances lithium ion concentration, reducing polarization and improving capacity retention at high discharge rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional single lithium salt electrolyte is used, then the battery structure is simple and manufacturing is easy, but the capacity retention at high discharge rates deteriorates due to increased internal resistance and polarization
Solution Approach 1:
The patent employs a composite electrolyte system containing multiple lithium salts (LiPF6, LiBF4, LiTFSI, LiFSO3) with specific molar ratios. This composite approach combines the advantages of different salts: LiPF6 provides high ionic conductivity, LiBF4 enhances thermal stability, LiTFSI improves low-temperature performance, and LiFSO3 reduces polarization. The synergistic effect of these composite salts resolves the contradiction by maintaining simple battery structure while achieving superior capacity retention at high discharge rates through optimized electrolyte composition.
Solution Approach 2:
The patent systematically optimizes the molar ratios of different lithium salts (LiPF6:LiBF4:LiTFSI:LiFSO3 = 0.8-1.2:0.1-0.3:0.1-0.3:0.1-0.3) and their concentrations (1.5M to 5M) to achieve the best performance. By adjusting these parameters, the electrolyte maintains low internal resistance and polarization at high discharge rates, thereby improving capacity retention without requiring complex battery structural modifications.
2Power
If high discharge rate is achieved, then power output increases, but polarization increases causing voltage drop and reduced capacity retention
Solution Approach 1:
The patent optimizes the concentration of lithium salts (1.5M to 5M) and their molar ratios to enhance ionic conductivity and reduce polarization. The specific composition (LiPF6:LiBF4:LiTFSI:LiFSO3 = 0.8-1.2:0.1-0.3:0.1-0.3:0.1-0.3) ensures that at high discharge rates, the electrolyte maintains sufficient Li+ transport capability, thereby reducing concentration polarization and voltage drop while preserving capacity retention.
Solution Approach 2:
The patent uses multiple lithium salt species that replicate and complement each other's functions. Each salt copy provides specific benefits: LiPF6 for conductivity, LiBF4 for stability, LiTFSI for low-temperature performance, and LiFSO3 for polarization reduction. This functional copying approach allows the electrolyte to maintain high power output capability while minimizing polarization effects at high discharge rates.
3Reliability
If lithium ion concentration is increased to reduce polarization, then capacity retention improves, but electrolyte complexity and manufacturing difficulty increase
Solution Approach 1:
The patent creates a composite electrolyte with multiple lithium salts at optimized concentrations (1.5M to 5M total). This composite formulation achieves high Li+ concentration and reduced polarization through the synergistic effects of different salts, while maintaining relatively simple manufacturing processes. The standardized composition ratios (LiPF6:LiBF4:LiTFSI:LiFSO3 = 0.8-1.2:0.1-0.3:0.1-0.3:0.1-0.3) facilitate consistent production without excessive complexity.
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 improved capacity retention of at least 10% at 10C or more, maintains performance at low temperatures, and demonstrates long service life with significant improvements in high voltage and high current output capabilities.
Implementation Method 1
The increase of Li+ concentration reduces polarization caused by a concentration difference of Li+ because of poor transportation of Li+ at high discharge rate. The concentration difference of Li+ between the electrode and electrolyte causes concentration polarization.
Data Source
AI summary
A lithium-based battery including an electrolyte having at least two lithium salts selected from LiPF6, LiTFSI, LiFSI or LiBF4, along with a further lithium salt additive. Through the selection of particular lithium salt combinations, a high lithium ion concentration in the electrolyte is maintained. The battery includes a cathode, an anode, and a porous polymer separator. The lithium-based battery has reliable capacity retention at high discharge rates, such as 10C to 15C.