Non-aqueous Electrolyte Salt Ratio for Battery Impedance and Durability
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Solution Overview
Problem
Current nonaqueous-electrolyte secondary batteries, particularly lithium secondary batteries, face challenges in achieving high initial charge capacity, low internal impedance, and durable input/output characteristics, especially at low temperatures and under high-temperature storage conditions, due to issues with electrolyte decomposition and uneven cell performance.
Innovation Solution
A nonaqueous electrolytic solution comprising LiPF6 and a fluorosulfonic acid salt represented by M(FSO3) in a specific proportion, which improves the battery's initial charge capacity, input/output characteristics, and internal impedance, while maintaining performance after durability tests.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LiPF6 is used as the sole electrolyte to achieve low internal impedance and high initial charge capacity, then the battery shows poor high-temperature durability and significant impedance increase after durability tests
Solution Approach 1:
The patent combines LiPF6 and LiFSO3 in a specific proportion (0.1-2.0 mol ratio) to create a composite electrolyte system. This merging of two different electrolyte salts allows the battery to simultaneously achieve low internal impedance (from LiPF6) and high-temperature durability (from LiFSO3), resolving the contradiction between initial performance and long-term reliability.
Solution Approach 2:
The electrolyte uses a composite salt system comprising LiPF6 and LiFSO3, where each component contributes different properties. LiPF6 provides high ionic conductivity and low impedance, while LiFSO3 provides thermal stability and resistance to decomposition at high temperatures. This composite approach allows the electrolyte to exhibit both excellent initial performance and superior durability.
2Reliability
If LiFSO3 is used as the sole electrolyte to achieve high discharge capacity and good cycle characteristics, then the battery exhibits high internal impedance and poor low-temperature output characteristics
Solution Approach 1:
The patent merges LiFSO3 (which provides good cycle characteristics) with LiPF6 (which provides low internal impedance and excellent input/output characteristics). The synergistic combination allows the electrolyte to simultaneously achieve reliable cycling performance and high power delivery, even at low temperatures.
Solution Approach 2:
The patent optimizes the molar ratio of LiFSO3 to LiPF6 within the range of 0.1-2.0 to balance the competing requirements. By adjusting this parameter, the electrolyte composition is tuned to achieve the optimal compromise between cycle life (from LiFSO3) and power characteristics (from LiPF6), ensuring both reliability and performance.
3Stability of the object's composition
If electrolyte decomposition is prevented to achieve high-temperature storability, then the battery shows reduced initial charge capacity and poor input/output characteristics
Solution Approach 1:
The electrolyte employs a composite salt system where LiFSO3 provides exceptional stability and resistance to decomposition at high temperatures, while LiPF6 maintains high ionic conductivity and charge capacity. The specific compositional ratio ensures that the stable component (LiFSO3) does not dominate to the extent of reducing initial capacity, nor does the high-performance component (LiPF6) decompose excessively at high temperatures.
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 batteries with lower internal impedance, improved low-temperature output characteristics, and enhanced high-temperature durability, retaining initial performance and capacity retention even after durability tests.
Implementation Method 1
a nonaqueous electrolytic solution which comprises: a nonaqueous solvent; LiPF6; and a fluorosulfonic acid salt represented by formula (1): M(FSO3)x
Implementation Method 2
a nonaqueous-electrolyte secondary battery which comprises: a negative electrode and a positive electrode capable of occluding and releasing lithium ions
Data Source
AI summary
An object of the invention is to provide a nonaqueous electrolytic solution which is capable of bringing about a nonaqueous-electrolyte secondary battery improved in initial charge capacity, input/output characteristics, and impedance characteristics, The invention relates to a nonaqueous electrolytic solution which comprises: a nonaqueous solvent; LiPF6; and a fluorosulfonic acid salt represented by formula (1): M(FSO3)x [wherein M is a metal atom, N(R)4, or P(R)4 (where R is either an organic group having 1-12 carbon atoms or a hydrogen atom (not all of the four R's are hydrogen atoms), the R's may be the same or different, and a part or all of the four R's may form a ring in cooperation with the nitrogen atom or phosphorus atom to which the R's have been bonded); when M is a metal atom, x indicates the valence of the metal atom M and is an integer of I or larger; and when M is N(R)4 or P(R)4, x is 1], wherein the ratio of the molar content of FSO3, in the nonaqueous electrolytic solution to the molar content of PF6 in the nonaqueous electrolytic solution is 0.001-1.2, and to a nonaqueous-electrolyte secondary battery containing the nonaqueous electrolytic solution.