Lithium Battery Electrolyte Stability at High Voltage
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Solution Overview
Problem
Lithium secondary batteries with nickel-based ternary-system positive electrodes face stability issues when using high charging voltages, particularly at increased temperatures, due to decomposition reactions and poor electrolyte stability.
Innovation Solution
A lithium secondary battery design incorporating a positive electrode with LiNi x Mn y Co z O 2 as the active material, paired with a nonaqueous electrolyte comprising fluorinated cyclic carbonate, propionate-based ester, and non-halogenated carbonate, maintaining a specific weight ratio, to enhance stability and prevent degradation at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a nickel-based ternary-system positive electrode material is used to raise charging voltage, then battery capacity is improved, but decomposition reaction occurs at the electrolyte causing deterioration of battery performance
Solution Approach 1:
The patent uses a composite electrolyte system combining fluorinated cyclic carbonate (FEC), propionate-based ester, and non-halogenated carbonate. This composite approach allows the electrolyte to simultaneously provide high voltage stability (from FEC), low viscosity and high ion conductivity (from propionate-based ester), and electrochemical stability (from non-halogenated carbonate), resolving the contradiction between capacity and reliability.
Solution Approach 2:
The patent optimizes the weight ratio of electrolyte components (FEC:propionate-based ester:non-halogenated carbonate = 20:80 to 50:50) to achieve the desired balance. By adjusting these parameters, the electrolyte maintains stability against decomposition at high charging voltages while preserving ion conductivity for high capacity operation.
2Speed
If service temperature increases to improve reaction kinetics, then charging/discharging rate is improved, but deterioration of battery performance becomes rapidly increasing
Solution Approach 1:
The patent utilizes the temperature-dependent properties of the propionate-based ester component, which maintains low viscosity across a wide temperature range. This allows the battery to achieve high charging/discharging rates at elevated temperatures without the rapid performance deterioration that would normally occur.
3Quantity of substance
If electrode density is increased to maximize utilization of battery inner space, then battery capacity is improved, but electrolyte with low viscosity and high ion conductivity is required which generally has bad stability against oxidation reaction
Solution Approach 1:
The patent employs a composite electrolyte where each component contributes specific properties: propionate-based ester provides low viscosity and high ion conductivity for dense electrode operation, while fluorinated cyclic carbonate (FEC) and non-halogenated carbonate provide oxidation stability. This composite approach resolves the contradiction between capacity and electrolyte stability.
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 achieves improved cycle characteristics and prevents performance degradation at high temperatures, ensuring stability and efficient charging/discharging performance even with increased positive electrode loading.
Implementation Method 1
an electrolytic composition electrochemically stable in a charge/discharge range of 0 to 4.2 V is required
Implementation Method 2
a negative electrode of a carbon-based material capable of intercalating and deintercalating lithium ions
Data Source
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AI summary
Disclosed is a lithium secondary battery including a positive electrode, a negative electrode, a separator and a nonaqueous electrolyte, wherein the positive electrode includes LiaNixMnyCozO2 (a+x+y+z=2, 0.9≤a≤1.1, 0≤x, 0≤y, 0≤z) as a positive electrode active material, and wherein the nonaqueous electrolyte includes (i) fluorinated cyclic carbonate expressed by Chemical Formula 1 below, (ii) propionate-based ester expressed by Chemical Formula 2 below, and (iii) non-halogenated carbonate, so that a mixture weight ratio (i : ii) thereof is 20:80 to 50:50: wherein, in Chemical Formula 1, R1, R2, R3 and R4 are independently any one of F, H and methyl group, and at least one thereof is F, wherein, in Chemical Formula 2, R5 is alkyl group having 1 to 5 carbons. The lithium secondary battery may ensure stability of an electrolyte even though a loading amount of a positive electrode is increased to implement a high-voltage battery system, thereby allowing excellent cycle characteristics of the battery. In addition, it is possible to prevent degradation of the battery performance at high-temperature storage.