Nonaqueous Electrolyte Composition for Fast Charging and HF Control
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Solution Overview
Problem
Nonaqueous secondary batteries face challenges with quick charging due to slow lithium ion diffusion, leading to insufficient charging capacity and voltage plateaus, and high-temperature durability issues caused by excessive HF generation, which affects battery safety and performance.
Innovation Solution
An acetonitrile-containing nonaqueous electrolyte solution with LiFSO3 as an HF generator, a buffer, and a specific content range to control HF generation, combined with a separator having an island structure of aggregated calcium to trap excess HF, and the use of lithium iron phosphate with an olivine-type structure to improve high-temperature cycle performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If quick charging is implemented at high charging speeds, then charging time is reduced, but lithium ion diffusion becomes insufficient leading to capacity loss and voltage plateaus
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte by introducing acetonitrile (5-97 vol%), LiFSO3 salt (0.1-10 mmol/L), and specific additives (vinylene carbonate 0.1-5 vol%, ethylene sulfite 0.1-5 vol%). These parameter changes enable the electrolyte to maintain high ionic conductivity for fast charging while forming stable SEI films to prevent capacity loss during quick charging cycles
Solution Approach 2:
The patent creates a composite electrolyte system combining multiple components: acetonitrile as base solvent, LiFSO3 as lithium salt, vinylene carbonate as film-forming additive, and ethylene sulfite as performance enhancer. This composite approach synergistically achieves both high charging speed capability and capacity retention by combining the benefits of each component
2Productivity
If LiPF6 is used as lithium salt to enhance ionic conductivity, then charging performance is improved, but excessive HF generation occurs at high temperature reducing battery safety
Solution Approach 1:
The patent converts the harmful effect of HF generation into a beneficial outcome by using LiFSO3 to generate controlled amounts of HF that form protective LiF layers on the negative electrode. The LiF layer acts as a stable SEI component that prevents further decomposition while the controlled HF generation avoids the excessive HF problems of LiPF6, thus converting potential harm into protective benefit
Solution Approach 2:
The patent changes the lithium salt from LiPF6 to LiFSO3, altering the chemical composition parameter to reduce excessive HF generation. Additionally, the patent optimizes the concentration of LiFSO3 (0.1-10 mmol/L) and adds HF-scavenging additives to control HF levels, transforming the high-temperature harmful effect into a manageable parameter that enhances overall battery safety
3Quantity of substance
If electrode thickness is increased to achieve high energy density, then energy capacity is improved, but lithium ion diffusion becomes slower reducing quick charging capability
Solution Approach 1:
The patent changes the electrolyte's physical parameters by using acetonitrile as the base solvent, which has low viscosity and high dielectric constant. This enables the electrolyte to maintain high ionic conductivity even with thick electrodes, allowing lithium ions to diffuse rapidly through the electrolyte to and from the thick electrode materials, thus resolving the diffusion bottleneck
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 inhibits capacity reduction during quick charging, prevents voltage plateaus, enhances lithium ion mobility for improved output performance, and maintains battery safety by controlling HF generation and trapping, while also improving high-temperature cycle performance.
Implementation Method 1
LiPF6 commonly contained in a nonaqueous electrolyte solution reacts with a trace amount of moisture in the nonaqueous electrolyte solution to generate HF, thus efficiently forming LiF which is a structural element of a negative electrode SEI
Implementation Method 2
when the separator comes into contact with a nonaqueous electrolyte solution, the silane crosslinking reaction of the silane-modified polyolefin proceeds to construct a silane crosslinked portion is the separator, thus achieving both low-temperature shutdown function and high-temperature fracture resistance. The silane crosslinking reaction proceeds using hydrogen fluoride (HF) generated by hydrolysis of LiPF6 contained in the nonaqueous electrolyte solution as a catalyst
Implementation Method 3
a silane crosslinked separator containing a trace amount of metal is used to trap an excess amount of HF which catalyzes a cleavage reaction at a silane crosslinked portion, thus improving long-term cycle characteristics of an electricity storage device
Data Source
AI summary
The present invention provides a nonaqueous electrolyte solution which contains: a nonaqueous solvent containing acetonitrile and vinylene carbonate; and a compound represented by general formula (1) R1-A-R2 (wherein A represents a divalent group that has a structure represented by one of formulae (1-2) to (1-5); and each of R1 and R2 independently represents an aryl group, an alkyl group which may be substituted by a halogen atom, while having from 1 to 4 carbon atoms, an alkyl group, a vinylidene group which may be substituted by a halogen atom, or an aryl group which may be substituted by a halogen atom; or alternatively, R1 and R2 may combine with each other and form, together with A, a ring structure that may have an unsaturated bond). With respect to this nonaqueous electrolyte solution, the total content of the vinylene carbonate and the compound represented by general formula (1) is not less than 0.1% by volume but less than 10% by volume relative to the total amount of the nonaqueous solvent; and the content of the vinylene carbonate is lower than the content of the compound represented by general formula (1).