Layered Rock-Salt Cathode Material for Battery Cycle Stability
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Solution Overview
Problem
Lithium-ion secondary batteries face challenges in maintaining charge and discharge capacity, cycle performance, reliability, safety, and cost due to degradation of positive electrode active materials during repeated charge and discharge cycles.
Innovation Solution
A positive electrode active material with a layered rock-salt structure, such as lithium cobalt oxide, is developed using a specific synthesis method involving initial heating and addition of additives like magnesium and fluorine to create a concentration gradient, enhancing the material's stability and capacity retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional positive electrode active materials are used in lithium-ion secondary batteries, then initial charge and discharge capacity can be achieved, but charge and discharge capacity decreases significantly during repeated charge and discharge cycles due to crystal structure breakdown
Solution Approach 1:
The patent changes the crystal structure parameter from conventional layered structures to a specific layered rock-salt structure with space group R-3m, characterized by specific lattice constants (a=2.81-2.85 Å, c=14.20-14.60 Å). This structural parameter change enhances stability during lithium ion insertion/extraction cycles, preventing capacity fade while maintaining high initial capacity.
Solution Approach 2:
The patent employs composite material design by combining lithium cobalt oxide with specific additives (magnesium and fluorine) to create a modified positive electrode active material. The additives form a concentration gradient distribution within the crystal structure, creating a composite system that leverages the high capacity of lithium cobalt oxide while the additives provide structural stabilization during cycling.
2Loss of substance
If high capacity positive electrode active materials are used, then charge and discharge capacity is improved, but crystal structure stability deteriorates during repeated charge and discharge cycles
Solution Approach 1:
The patent applies local quality by creating a non-uniform concentration distribution of additives (magnesium and fluorine) within the crystal structure. The additives are distributed with higher concentration at specific regions (surface or subsurface) rather than uniformly throughout, providing localized structural reinforcement where it is most needed to prevent crystal breakdown during high-capacity cycling.
Solution Approach 2:
The patent modifies the crystal structure parameters by incorporating additives that alter lattice constants and interlayer spacing. The specific layered rock-salt structure with controlled lattice parameters provides both high capacity and enhanced structural stability, resolving the trade-off between capacity and stability.
3Reliability
If conventional synthesis methods are used for positive electrode active materials, then manufacturing simplicity is maintained, but charge and discharge capacity and cycle performance are insufficient
Solution Approach 1:
The patent applies preliminary action by performing initial heating treatment at 500-1000°C for 1-24 hours before final synthesis. This pre-treatment step prepares the crystal structure by removing impurities and forming a preliminary layered rock-salt framework, which then facilitates the subsequent additive incorporation and final crystal growth, ensuring high cycle performance while maintaining reasonable manufacturing complexity.
Solution Approach 2:
The patent employs specific synthesis parameter changes including controlled heating temperatures (500-1000°C), extended heating times (1-24 hours), and precise additive ratios (0.01-5 wt% each). These parameter optimizations transform a simple synthesis process into one that produces materials with exceptional cycle performance, achieving high reliability through carefully controlled manufacturing parameters.
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 provides a positive electrode active material that maintains high charge and discharge capacity, cycle performance, and safety by preventing crystal structure breakdown during repeated cycles, thereby improving the reliability and efficiency of lithium-ion secondary batteries.
Implementation Method 1
a positive electrode active material or a composite oxide which inhibits a decrease in charge and discharge capacity due to charge and discharge cycles
Implementation Method 2
a positive electrode active material or a composite oxide whose crystal structure is not easily broken even when charge and discharge are repeated
Data Source
AI summary
A battery in which a decrease in discharge capacity retention rate in charge and discharge cycle tests is inhibited is provided. The battery includes a positive electrode and a negative electrode. The positive electrode is used as a positive electrode of a test battery in which a negative electrode includes a lithium metal. When a test of 50 repetitions of a cycle of charge and discharge in which, after constant current charge is performed at a charge rate of 1 C (1 C=200 mA/g) until a voltage of 4.6 V is reached, constant voltage charge is performed at a voltage of 4.6 V until the charge rate reaches 0.1 C, and constant current discharge is then performed at a discharge rate of 1 C until a voltage of 2.5 V is reached is performed in a 25° C. environment or a 45° C. environment and discharge capacity is measured in each cycle, a discharge capacity value measured in a 50th cycle accounts for higher than or equal to 90% and lower than 100% of a maximum discharge capacity value in all 50 cycles.