Acetonitrile Electrolyte SEI Design for High-Temperature Li-Ion Batteries
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Solution Overview
Problem
Acetonitrile-based electrolyte solutions in lithium ion batteries face issues with reductive decomposition at high temperatures, leading to gas generation and capacity reduction, while a robust film on the negative electrode inhibits lithium ion conductivity.
Innovation Solution
A non-aqueous electrolyte solution containing PO2F2 anions and cyclic acid anhydride is used to form a solid electrolyte interface (SEI) on the negative electrode, suppressing reductive decomposition and maintaining ion conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a highly durable film is formed on the negative electrode to suppress reductive electrolysis, then gas generation and capacity reduction are suppressed, but insertion or dissociation of lithium ions is inhibited, reducing ion conductivity
Solution Approach 1:
The patent applies local quality by creating an SEI film with spatially varying properties: an inner layer with high durability to suppress reductive decomposition, and an outer layer with high ion conductivity to facilitate lithium ion transport. This is achieved through specific additive combinations (cyclic carboxylic acid and its derivative) that form differentiated film structures at different depths of the negative electrode surface.
Solution Approach 2:
The patent employs composite materials by combining multiple electrolyte additives (cyclic carboxylic acid and its derivative) that work synergistically to form a composite SEI film structure. This composite film integrates the protective function of the inner layer with the conductive function of the outer layer, resolving the contradiction between durability and ion conductivity.
2Productivity
If acetonitrile is used as the electrolyte solvent to achieve high ion conductivity, then low-temperature characteristics are improved, but reductive decomposition occurs at high temperatures, causing gas generation and capacity reduction
Solution Approach 1:
The patent applies preliminary action by having the cyclic carboxylic acid and its derivative additives form a protective SEI film on the negative electrode before acetonitrile can undergo harmful reductive decomposition at high temperatures. This pre-formed film acts as a barrier that prevents direct contact between acetonitrile and the electrode, thereby maintaining high-temperature stability while preserving the ion conductivity benefits of acetonitrile.
Solution Approach 2:
The patent uses cyclic carboxylic acid and its derivative as intermediary substances that mediate between the acetonitrile solvent and the negative electrode. These additives form the SEI film that serves as an intermediate layer, allowing ion conductivity to pass through while preventing direct reductive decomposition reactions between acetonitrile and the electrode at high temperatures.
3Duration of action of stationary object
If a robust SEI film is formed to prevent reductive decomposition, then high-temperature durability is improved, but lithium ion insertion and dissociation are inhibited, reducing battery performance
Solution Approach 1:
The patent applies local quality by creating a vertically differentiated SEI film structure where the inner layer (close to the electrode) provides high durability for long service life, while the outer layer provides high ion conductivity for fast charge-discharge rates. The cyclic carboxylic acid and its derivative additives enable this spatial differentiation of film properties.
Solution Approach 2:
The patent employs composite materials by forming a composite SEI film with distinct functional layers through the synergistic action of cyclic carboxylic acid and its derivative. The inner layer composite provides structural stability and durability, while the outer layer composite provides ion transport pathways, thereby achieving both long service life and high charge-discharge rates.
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 delays gas generation at high temperatures, prevents battery swelling, and maintains excellent low-temperature and high-temperature characteristics, ensuring stable battery performance across a wide temperature range.
Implementation Method 1
it is known that an acetonitrile-based electrolyte solution is required to form a film on a surface of a negative electrode in order to suppress reductive electrolysis
Implementation Method 2
reductive decomposition proceeds at the time of initial charging or each test under a high-temperature environment to cause gas generation, capacity reduction, or the like
Implementation Method 3
form a film on a surface of a negative electrode in order to suppress reductive electrolysis
Implementation Method 4
a lithium cell, having positive and negative electrodes capable of occluding and releasing lithium
Data Source
Figure 1
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Figure 3~3(b)
AI summary
To provide a non-aqueous electrolyte solution, a non-aqueous secondary battery, a cell pack, and a hybrid power system, capable of improving desired battery performance in an acetonitrile electrolyte solution, the non-aqueous electrolyte solution contains a non-aqueous solvent, PO2F2 anions, and cyclic acid anhydride. The non-aqueous electrolyte battery includes a positive electrode having a positive-electrode active material layer formed on one surface or both surfaces of a current collector, a negative electrode having a negative-electrode active material layer formed on one surface or both surfaces of a current collector, and a non-aqueous electrolyte solution. The non-aqueous electrolyte solution contains acetonitrile and LiPO2F2. A value obtained by dividing a bulk resistance at a temperature of -30°C by an internal resistance value in FRA measurement for the non-aqueous electrolyte battery is in a range of 0.05 to 0.7. The non-aqueous secondary battery has a capacity retention rate of 70% or higher, where the capacity retention rate is calculated by dividing a 5C discharge capacity by a 1C discharge capacity after a storage test for four hours at 85°C.