Wound Battery Electrolyte Composition for Low-Temperature Cycle Stability
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Solution Overview
Problem
Batteries with existing structures experience deteriorated cycle characteristics in low temperature environments due to insufficient suppression of metallic lithium precipitation on the negative electrode, leading to increased battery resistance and heat generation during charge and discharge.
Innovation Solution
A battery design with band-shaped positive and negative electrodes having active material covered and non-covered portions, bonded to current collecting plates, and an electrolytic solution composition of 7.7-11.5% fluoroethylene carbonate and 0.032-0.048% lithium tetrafluoroborate, along with lithium hexafluorophosphate, to improve cycle characteristics and reduce resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the content of FEC in the electrolytic solution is increased to suppress metallic lithium precipitation, then cycle characteristics are improved, but decomposition of FEC increases and gas generation occurs
Solution Approach 1:
The patent optimizes the concentration parameters of FEC (2-50 vol%) and LiBF4 (0.1-1.0 mol/liter) in the electrolytic solution to achieve the desired balance between suppressing lithium precipitation and preventing FEC decomposition. By carefully adjusting these chemical parameters, the system achieves improved cycle characteristics while minimizing gas generation from FEC decomposition.
Solution Approach 2:
LiBF4 acts as an intermediary substance that suppresses the decomposition of FEC. The presence of LiBF4 in the electrolytic solution prevents FEC from decomposing during charge storage, thereby suppressing gas generation while allowing FEC to effectively suppress metallic lithium precipitation on the negative electrode.
2Loss of energy
If the battery resistance is reduced to minimize heat generation, then energy efficiency is improved, but suppression of metallic lithium precipitation in low temperature environments becomes insufficient
Solution Approach 1:
The patent adjusts the concentration of FEC in the electrolytic solution to a specific range (2-50 vol%, preferably 10-30 vol%) to optimize the balance between maintaining low battery resistance and effectively suppressing metallic lithium precipitation in low temperature environments. This parameter optimization ensures both energy efficiency and reliable cycle characteristics across temperature conditions.
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 effectively suppresses metallic lithium precipitation and gas generation, enhancing cycle stability and reducing internal resistance, allowing for high-rate discharge and improved low-temperature performance without excessive gas production.
Implementation Method 1
precipitation of metallic lithium generated on the surface of a negative electrode by the action of FEC can be suppressed
Implementation Method 2
decomposition of FEC during charge storage can be suppressed by the action of LiBF4, so that generation of gas associated with decomposition can be suppressed
Data Source
AI summary
Provided is a battery having excellent cycle characteristics in a low temperature environment. A battery includes components housed in an exterior can, the components including: an electrode wound body having a structure in which a band-shaped positive electrode including a positive-electrode foil and a positive-electrode active material layer and a band-shaped negative electrode including a negative-electrode foil and a negative-electrode active material layer are stacked with a separator interposed therebetween and wound around a central axis; a positive-electrode current collecting plate; a negative-electrode current collecting plate; and an electrolytic solution, in which the electrode foil has an electrode active material covered portion covered with the active material layer and an active material non-covered portion not covered with the active material layer, a surface on which the active material non-covered portion bent toward the central axis overlaps and the current collecting plate are bonded to each other, and the electrolytic solution contains 7.7 mass % or more and 11.5 mass % or less of fluoroethylene carbonate, 0.032 mass % or more and 0.048 mass % or less of lithium tetrafluoroborate, and lithium hexafluorophosphate.