Lithium-Ion Battery Electrolyte Additives for SEI Film Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Lithium-ion secondary batteries face challenges with low cycle performance and discharging efficiency, especially at low temperatures, due to the oxidation and reduction of solvents during charging-discharging processes, and existing additives either form thick SEI films that increase impedance or fail to improve low-temperature performance.
Innovation Solution
The use of a composite electrolyte containing vinylene carbonate, vinyl ethylene carbonate, and derivatives of 4-methylene-1,3-dioxolan-2-one and 4,5-dimethylene-1,3-dioxolan-2-one, which form a compact SEI film with lower impedance, enhancing lithium ion transfer and preventing reactions between the negative electrode and electrolyte, thereby improving cycle and low-temperature discharging performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If vinylene carbonate (VC) is added into the electrolyte to form an SEI film on the negative electrode plate, then the first coulombic efficiency and cycle performance are improved, but the SEI film becomes too thick, the impedance increases, and the low temperature discharging performance deteriorates
Solution Approach 1:
The patent uses a composite additive system combining vinylene carbonate (VC) with 4-methylene-1,3-dioxolan-2-one and/or 4,5-dimethylene-1,3-dioxolan-2-one. This composite approach creates a synergistic effect where VC provides the base SEI film structure while the dioxolan-2-one derivatives modify the film properties to reduce thickness and impedance, thereby improving low temperature discharging performance while maintaining cycle performance benefits.
Solution Approach 2:
The patent optimizes the concentration parameters of the additives in the electrolyte. VC is used at 0.01-2.0 wt% and the dioxolan-2-one derivatives are used at 0.01-5.0 wt%. By precisely controlling these parameter ranges, the SEI film forms with optimal thickness and composition, balancing protection benefits against impedance concerns, particularly improving low temperature performance.
2Reliability
If the SEI film thickness is increased to improve cycle performance, then the first coulombic efficiency improves, but the impedance of the SEI film increases and low temperature discharging performance deteriorates
Solution Approach 1:
The patent employs a composite SEI film formed by multiple additives working together. VC provides the primary film structure while the dioxolan-2-one derivatives (4-methylene-1,3-dioxolan-2-one and/or 4,5-dimethylene-1,3-dioxolan-2-one) act as modifiers that control film growth, resulting in a thinner, lower-impedance film that maintains protective functions while enabling better low temperature operation.
Solution Approach 2:
The patent creates an SEI film with non-uniform properties through the composite additive system. The film has different compositions and structures at different locations and depths, with the dioxolan-2-one derivatives concentrating in specific regions to reduce impedance locally while maintaining overall film integrity for cycle performance.
3Productivity
If conventional solvents are used in the electrolyte, then the battery can operate, but the solvents are continuously oxidized or reduced during charging-discharging, resulting in low first coulombic efficiency and deteriorated cycle performance
Solution Approach 1:
The patent uses VC and dioxolan-2-one derivatives to pre-form a stable SEI film on the negative electrode during initial cycles. This preliminary protective layer prevents subsequent continuous oxidation and reduction of the electrolyte solvents during normal operation, thereby improving both first coulombic efficiency and long-term cycle performance by eliminating the harmful side reactions.
Solution Approach 2:
The SEI film formed by VC and doxolan-2-one derivatives acts as an intermediary protective layer between the negative electrode and the electrolyte solvent. This intermediate layer blocks direct contact between the solvent and electrode, preventing continuous oxidation and reduction reactions, thus improving both efficiency and cycle life.
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 composite electrolyte significantly improves the first coulombic efficiency, cycle performance, and low-temperature discharging capacity retention rate of lithium-ion secondary batteries by forming a compact SEI film that prevents by-reactions and maintains high lithium ion conductivity.
Implementation Method 1
adding vinylene carbonate (VC) into an electrolyte, in which the first coulombic efficiency and the cycle performance of the lithium-ion secondary battery are improved by forming a SEI film on a surface of a negative electrode plate
Implementation Method 2
the composite SEI film, which is good for lithium ion transfer, can be formed on the surface of the negative electrode plate
Data Source
AI summary
The present disclosure provides a lithium-ion secondary battery and an electrolyte thereof. The electrolyte comprises a lithium salt; a non-aqueous solvent and an additive comprising a first additive and a second additive, the first additive comprises at least one of vinylene carbonate and vinyl ethylene carbonate, the second additive is 4-methylene-1,3-dioxolan-2-one and its derivatives with a structural formula 1 and/or 4,5-dimethylene-1,3-dioxolan-2-one and its derivatives with a structural formula 2; in the structural formula 1 and the structural formula 2, R1, R2, R3 and R4 each are hydrogen, halogen, C1˜C3 alkyl or halogenated alkyl; a weight percentage of the first additive in the electrolyte is 0.2%˜2.0%, a weight percentage of the second additive in the electrolyte is 0.3%˜4.0%. The lithium-ion secondary battery comprises the aforementioned electrolyte. The lithium-ion secondary battery has better cycle performance, better low temperature discharging performance, and higher first coulombic efficiency.