Nonaqueous Electrolyte Film Formation for Battery Reliability
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Solution Overview
Problem
Conventional lithium-ion secondary batteries using propylene carbonate as a nonaqueous solvent face issues with decomposition, leading to gas generation, capacity decrease, and deterioration of charging/discharging characteristics, especially at high temperatures, and fail to achieve sufficient reliability and high-rate discharging performance.
Innovation Solution
A nonaqueous electrolytic solution with a specific composition that includes propylene carbonate, 1,3-propane sultone, and vinylene carbonate, where the content of these components satisfies certain mass percentage conditions to form a chemically stable protective film on the negative electrode, enhancing the battery's initial power generation efficiency, high-rate discharging characteristic, and charging/discharging cycle performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If propylene carbonate is used as a nonaqueous solvent to achieve high conductivity and wide potential window, then the battery can provide good ionic conductivity, but decomposition occurs at the negative electrode during charging causing gas generation and capacity decrease
Solution Approach 1:
The patent introduces 1,3-propane sultone and vinylene carbonate as intermediary substances that form a protective film on the negative electrode surface. This film acts as a mediator between propylene carbonate and the graphite electrode, preventing direct contact and decomposition while allowing lithium ion transport. The additives sacrifice themselves to create this protective interface, solving the contradiction between maintaining high ionic conductivity and preventing decomposition.
Solution Approach 2:
The patent changes the chemical composition parameters of the electrolyte by adding specific amounts of 1,3-propane sultone (0.1-5 mass%) and vinylene carbonate (0.1-5 mass%) to propylene carbonate. This parameter modification transforms the electrolyte system from one that causes decomposition to one that forms a stable protective film, resolving the contradiction between conductivity and decomposition resistance.
2Reliability
If conventional additives like 1,3-propane sultone or vinylene carbonate are added to suppress decomposition, then gas generation is reduced, but high-rate discharging characteristic is insufficient
Solution Approach 1:
The patent merges 1,3-propane sultone and vinylene carbonate into a synergistic combination within specific ratio ranges. This combined approach creates a more effective protective film than either additive alone, achieving both decomposition suppression and improved high-rate discharging characteristics. The synergistic effect resolves the contradiction by making the protective film both more stable and more conductive.
Solution Approach 2:
The patent optimizes the concentration parameters of both additives simultaneously, specifying 1,3-propane sultone at 0.1-5 mass% and vinylene carbonate at 0.1-5 mass% with specific ratio relationships. This dual-parameter optimization creates a protective film with balanced properties: sufficient chemical stability for decomposition suppression and adequate ionic conductivity for high-rate discharging.
3Quantity of substance
If the negative electrode uses highly crystallized graphite for high capacity, then energy density is improved, but propylene carbonate decomposition is accelerated
Solution Approach 1:
The patent uses 1,3-propane sultone and vinylene carbonate as intermediary substances that form a protective interface film on the highly crystallized graphite surface. This film acts as a barrier that prevents propylene carbonate from directly contacting and decomposing at the graphite electrode, while still allowing lithium ions to intercalate and deintercalate efficiently. This resolves the contradiction by protecting the high-capacity graphite electrode from decomposition.
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 gas generation and maintains battery reliability and performance even at elevated temperatures, achieving excellent initial power generation efficiency, high-rate discharging, and charging/discharging cycle characteristics.
Implementation Method 1
the content X [mass %] of the first compound and the content Y [mass %] of the second compound simultaneously satisfy the conditions represented by the following expressions (1) and (2): 2≦(X+Y)≦8 and 0.01≦(Y/X)≦0.30
Implementation Method 2
the chemical stability of the film is insufficient, whereby a sufficient charging/discharging cycle characteristic is not obtained
Implementation Method 3
the decomposition of propylene carbonate proceeds, a gas is generated, with which the carbon material of the negative electrode peels off, decomposes, etc.
Implementation Method 4
a nonaqueous electrolytic solution including a nonaqueous solvent and a lithium salt soluble in the nonaqueous solvent
Data Source
AI summary
A nonaqueous solvent in a nonaqueous electrolytic solution in a lithium-ion secondary battery 1 contains propylene carbonate (PC), a first compound expressed by formula (I), and a second compound expressed by formula (II). The content of PC in the nonaqueous solvent is at least 10 volume %. The content X [mass %] of the first compound and the content Y [mass %] of the second compound simultaneously satisfy the conditions represented by expressions (1) and (2) [2≦(X+Y)≦8 (1), 0.01≦(Y/X)≦0.30 (2)]. R1 to R6 in formula (I) indicate any of a hydrogen atom and hydrocarbon groups having a carbon number of 1 to 3, whereas R7 and R8 in formula (II) indicate any of a hydrogen atom and hydrocarbon groups having a carbon number of 1 to 3.