Fluorinated Phosphate Electrolyte for High-Voltage Lithium Batteries
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Solution Overview
Problem
Lithium secondary batteries with high voltage positive electrodes face challenges in maintaining life due to easy decomposition of electrolytic solutions, leading to reduced capacity retention and shortened lifespan, despite existing additives providing insufficient oxidation resistance.
Innovation Solution
A lithium secondary battery utilizing a nonaqueous electrolytic solution with a fluorine-containing phosphate compound, featuring a general formula O=P(O—R1)(O—R2)(O—R3), where R1, R2, and R3 include ether bonds and fluorine, enhancing oxidation resistance and film stability on the electrode surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a high potential positive electrode active material (4.5 V or more vs lithium) is used to increase energy density, then the operating voltage and energy density are improved, but the decomposition reaction of the electrolytic solution proceeds easily leading to shortened battery life
Solution Approach 1:
A fluorine-containing phosphate compound is introduced as an intermediary substance in the nonaqueous electrolytic solution. This compound mediates between the high potential positive electrode and the conventional electrolyte components, forming a stable interface layer that prevents direct harmful reactions while allowing ionic conduction, thus enabling high voltage operation without sacrificing battery life
Solution Approach 2:
The chemical composition parameters of the electrolytic solution are changed by incorporating a fluorine-containing phosphate compound with specific molecular structure (formula (1)). This parameter change modifies the electrochemical stability window and interfacial properties of the electrolyte, enabling it to withstand higher potentials without decomposition
2Reliability
If conventional electrolytic solution additives are used to improve battery life, then a protective film is formed on the negative electrode, but the remaining additive components react with the high potential positive electrode causing capacity loss and gas generation
Solution Approach 1:
The fluorine-containing phosphate compound acts as a selective intermediary that preferentially interacts with the high potential positive electrode surface. It forms a stable protective layer on the positive electrode, preventing reactions between conventional additives and the positive electrode, while still allowing negative electrode protection mechanisms to function
Solution Approach 2:
The electrolytic solution exhibits different functional properties at different locations: the fluorine-containing phosphate compound specifically targets and forms protective films on the high potential positive electrode surface, while leaving the negative electrode environment relatively unchanged, thus providing location-specific protection against oxidation
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 battery exhibits improved life characteristics and capacity retention, especially at high potentials, with the fluorine-containing phosphate compound effectively suppressing oxidation reactions and maintaining ionic conductivity.
Implementation Method 1
the additive component remaining in the electrolytic solution reacts with the high potential positive electrode, which may cause the lowering of the capacity retention ratio and the generation of gas
Implementation Method 2
there is room for improvement for an additive having further oxidation resistance
Implementation Method 3
the nonaqueous electrolytic solution comprises a phosphate compound represented by the following general formula (1)
Data Source
AI summary
An embodiment of the present invention relates to a lithium secondary battery comprising a nonaqueous electrolytic solution comprising a phosphate compound represented by the following general formula (1): O═P(O—R1)(O—R2)(O—R3) (1), wherein R1, R2, and R3 are each alkyl group or the like or a group comprising an ether bond represented by —R4—O—R5 (R4 represents alkylene group, and R5 represents alkyl group), and at least one of R1, R2, and R3 is a group comprising an ether bond, and at least one of R1, R2, and R3 contains fluorine, and a positive electrode active material having a charge and discharge region of 4.5 V or more versus lithium.