Non-Aqueous Electrolyte Tuning for High-Nickel Cathode Durability
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Solution Overview
Problem
Non-aqueous secondary batteries with high nickel ratio positive electrode active materials suffer from poor long-term durability and high-temperature performance due to cracking and spinel transition, exacerbated by high ionic conductivity electrolytes that cause lithium extraction and structural instability.
Innovation Solution
A non-aqueous secondary battery design with a positive electrode containing a lithium-containing metal oxide and a coating layer, using a non-aqueous electrolyte solution with acetonitrile in a specific concentration range and ionic conductivity, and a dinitrile compound to stabilize the crystal structure and inhibit lithium extraction, thereby controlling the c-axis lattice constant change and reducing cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high nickel ratio positive electrode active material is used to increase capacity, then energy density is improved, but long-term durability deteriorates due to cracking and spinel transition
Solution Approach 1:
The patent applies parameter changes by precisely controlling the c/a axis ratio of the positive electrode active material within 1.80-1.95 and the crystallite size within 0.5-5 μm. These parameter optimizations reduce expansion and contraction during charging and discharging, thereby suppressing cracking and spinel transition while maintaining high nickel ratio for high energy density
Solution Approach 2:
The patent uses composite materials by combining high nickel ratio positive electrode active material with specifically formulated non-aqueous electrolyte containing fluoroethylene carbonate and acetonitrile. This composite system achieves both high capacity and improved cycle characteristics by suppressing deterioration mechanisms
2Productivity
If high ionic conductivity electrolyte is used to improve performance, then capacity is improved, but positive electrode structural stability deteriorates due to lithium extraction
Solution Approach 1:
The patent changes electrolyte composition parameters by incorporating fluoroethylene carbonate and acetonitrile in specific proportions, achieving optimal balance between ionic conductivity and structural stability. The electrolyte composition is optimized to prevent excessive lithium extraction while maintaining high capacity
Solution Approach 2:
The patent introduces fluoroethylene carbonate and acetonitrile as intermediary substances that mediate between the high ionic conductivity requirement and structural stability. These additives form protective interfaces and regulate lithium extraction, preventing direct harmful interactions between the electrolyte and positive electrode structure
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 inhibits deterioration and maintains high capacity and cycle performance even at high temperatures, ensuring excellent long-term durability and high-temperature stability by stabilizing the positive electrode active material structure.
Implementation Method 1
a dinitrile compound stabilizes the crystal structure and inhibits lithium extraction, thereby controlling the c-axis lattice constant change
Implementation Method 2
non-aqueous electrolyte solutions having high ionic conductivity... acetonitrile has a high potential... excellent balance between the viscosity and the dielectric constant
Implementation Method 3
expansion and contraction of a positive electrode during charging and discharging are reduced and the cycle characteristics at a high voltage are improved by defining the c/a axis ratio of the positive electrode to be in a prescribed range
Data Source
AI summary
Provided is a non-aqueous secondary battery that includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. The positive electrode includes LiNixCoyMnzO2 (0.7<x<0.9, 0<y<0.2, 0<z<0.2) as a lithium-containing metal oxide, and when the positive electrode before and after cycle testing of the non-aqueous secondary battery is analyzed by powder X-ray diffraction using Cu-Kα radiation, the rate of change of the c-axis lattice constant is 1.0% or less. The non-aqueous electrolyte includes 5-20% by volume of acetonitrile and has an ion conductivity of at least 10 mS/cm and less than 15 mS/cm at 20° C.