Nonaqueous electrolyte energy storage device with FEC
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Solution Overview
Problem
Nonaqueous electrolyte energy storage devices with fluorinated cyclic carbonates and graphite electrodes face increased internal resistance, limiting their high discharge capacity when charged at high end-of-charge voltages.
Innovation Solution
A nonaqueous electrolyte energy storage device with a nonaqueous solvent containing fluorinated cyclic carbonate and an electrolyte salt, featuring a negative electrode with a higher mass ratio of graphite to hardly graphitizable carbon, and a reduced electrolyte salt concentration below 2.0 mol/l, which enhances discharge capacity and reduces internal resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fluorinated cyclic carbonate (FEC) is added to the nonaqueous electrolyte to improve charge-discharge cycle performance, then cycle performance is improved, but internal resistance increases
Solution Approach 1:
The patent optimizes the concentration of FEC in the nonaqueous electrolyte to a specific range (5-30 vol%) to achieve the desired balance between cycle performance and internal resistance. This parameter optimization allows the electrolyte to form a stable SEI layer that improves cycle life while controlling the increase in internal resistance.
Solution Approach 2:
The patent uses a composite electrolyte system combining fluorinated cyclic carbonate (FEC) with other cyclic carbonate solvents (EC, PC) and chain carbonate solvents (DMC, DEC, EMC). This composite approach leverages the benefits of FEC for SEI formation and cycle stability while using the other solvents to maintain low internal resistance and high ionic conductivity.
2Quantity of substance
If the nonaqueous electrolyte contains fluorinated cyclic carbonate and graphite is used in the negative electrode, then capacity is improved, but internal resistance increases
Solution Approach 1:
The patent optimizes the ratio of graphite to hardly graphitizable carbon in the negative electrode within specific ranges (graphite: 70-95 wt%, hardly graphitizable carbon: 5-30 wt%). This composition optimization ensures high discharge capacity while controlling internal resistance by balancing the high capacity of graphite with the structural stability of hardly graphitizable carbon.
Solution Approach 2:
The patent creates a composite negative electrode using both graphite and hardly graphitizable carbon materials. This composite structure combines the high capacity advantage of graphite with the dimensional stability and low resistance characteristics of hardly graphitizable carbon, achieving both high capacity and acceptable internal resistance.
3Reliability
If electrolyte salt concentration is increased to improve ionic conductivity, then conductivity is improved, but internal resistance increases due to FEC interaction
Solution Approach 1:
The patent optimizes the electrolyte salt concentration to a specific range (1.0-2.0 mol/L) to balance ionic conductivity and internal resistance. This optimized concentration ensures sufficient lithium ion transport for high conductivity while preventing excessive FEC-salt complex formation that would increase internal resistance.
Solution Approach 2:
The patent adjusts the FEC concentration within a specific range (5-30 vol%) to optimize the balance between SEI formation and ionic conductivity. This parameter control ensures that FEC provides adequate SEI protection without forming excessive resistant complexes with the electrolyte salt, maintaining low internal resistance.
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 reduces internal resistance and maintains high discharge capacity when charged at high end-of-charge voltages, ensuring a wide range of depth of discharge and high energy density.
Implementation Method 1
configured to perform charge-discharge by delivering ions between both the electrodes
Implementation Method 2
it is known that when a nonaqueous electrolyte contains fluorinated cyclic carbonate such as fluoroethylene carbonate (FEC), the charge-discharge cycle performance of a nonaqueous electrolyte energy storage device using the nonaqueous electrolyte is improved
Data Source
Figure 1~2
Figure 3~5
AI summary
A nonaqueous electrolyte energy storage device according to the present invention is a nonaqueous electrolyte energy storage device including: a nonaqueous electrolyte containing a nonaqueous solvent containing fluorinated cyclic carbonate, and an electrolyte salt; and a negative electrode containing graphite and hardly graphitizable carbon. The mass of the graphite is larger than the mass of the hardly graphitizable carbon, and the content of the electrolyte salt in the nonaqueous electrolyte is less than 2.0 mol/l.