Over-Lithiated Cathode Composition for Stable High-Capacity Cycling
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Solution Overview
Problem
Lithium secondary batteries using over-lithiated oxide particles exhibit low operational stability and capacity, particularly due to the unique electrochemical reactions of Li 2 MnO 3 domains.
Innovation Solution
A cathode for lithium secondary batteries is designed with over-lithiated oxide particles represented by Formula Li a [M x Ni y Mn z ]O b, where D > 5, and an upper limit of operating voltage is 4.5 V or less, enhancing the crystal structure disorder and improving lifespan characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If over-lithiated oxide particles are used as cathode active material, then capacity is improved (reversible capacity of 250 mAh/g or more), but operational stability deteriorates (reduced lifespan characteristics)
Solution Approach 1:
The invention changes the crystal structure parameters of the over-lithiated oxide particles by controlling the ratio of Li2MnO3 domains to LiMO2 domains, and by adjusting the composition ratios of transition metals (Ni, Mn, Co) to achieve a disorder parameter D greater than 5, thereby improving operational stability while maintaining high capacity
Solution Approach 2:
The invention uses composite over-lithiated oxide particles containing both Li2MnO3 domains and LiMO2 domains in a specific ratio, combining the high capacity特性 of Li2MnO3 with the structural stability of LiMO2 to achieve both high capacity and improved operational stability
2Quantity of substance
If lithium is inserted into transition metal site to form over-lithiated oxide, then reversible capacity increases to 250 mAh/g or more, but crystal structure stability decreases leading to transition metal migration
Solution Approach 1:
The invention changes the crystal structure parameters by controlling the disorder parameter D to be greater than 5, which is achieved by adjusting the composition ratios of transition metals and the domain ratio between Li2MnO3 and LiMO2, thereby preventing transition metal migration while maintaining high reversible capacity
Solution Approach 2:
The invention creates local structural differences by forming distinct Li2MnO3 domains and LiMO2 domains within the particle structure, where each domain has different local composition and structure properties, allowing the material to achieve high capacity while maintaining overall structural 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 cathode achieves high capacity and improved lifespan characteristics by increasing the disorder in the crystal structure, with D values greater than 5, leading to better transition metal migration and retention during charging and discharging.
Implementation Method 1
The over-lithiated oxide particles may exhibit a reversible capacity of 250 mAh/g or more by an electrochemical reaction of Li2MnO3
Implementation Method 2
The lithium secondary battery may store an electric energy by a difference in chemical potential when lithium ions are intercalated and deintercalated between a cathode and an anode
Implementation Method 3
Li2MnO3 is electrochemically inactive, but may be converted into LiMnO2 as shown in Scheme 1 below by an activation process (e.g., charging and discharging a lithium secondary battery using over-lithiated oxide particles at 4.4 V (vs Li/Li+)
Implementation Method 4
Li2MnO3 is electrochemically inactive, but may be converted into LiMnO2 as shown in Scheme 1 below by an activation process
Data Source
Figure 1~3
AI summary
A cathode for a lithium secondary battery according to exemplary embodiments may include a cathode current collector; and a cathode active material layer formed on the cathode current collector and including over-lithiated oxide particles. A D value represented by Equation 1 of the cathode may be greater than 5.