Li2MnO3-Like Cathode Material for High Voltage Stability
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Solution Overview
Problem
Current cathode active materials for high voltage lithium secondary batteries face challenges in achieving high capacity and structural stability, with existing materials like LiCoO2 being expensive and unstable, and lithium manganese oxides having low capacity and poor high-temperature characteristics.
Innovation Solution
A lithium transition metal oxide with a composition represented by Formula Li1+aNibCocMn1−(a+b+c+d)O2-tAt, where 0.05≦a≦0.2, 0.4≦b≦0.7, 0.1≦c≦0.4, 0≦d≦0.1, and 0≦t<0.2, and M being a divalent or trivalent metal, and A a monovalent or divalent anion, which has a Li2MnO3-like structure phase and a lithium molar fraction greater than 1, providing enhanced capacity and stability at high voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LiCoO2 is used as cathode active material, then excellent lifespan characteristics and charge-discharge efficiencies are achieved, but high cost and low safety at high temperature result
Solution Approach 1:
The patent uses composite materials by combining Li2MnO3 (providing structural stability and cost advantage) with LiMO2 (providing electrochemical activity and high capacity). This composite approach allows the cathode to achieve both excellent lifespan characteristics and cost-effectiveness while maintaining high temperature safety, resolving the contradiction between reliability and manufacturing cost.
2Stability of the object's composition
If Li2MnO3 is used as cathode active material, then very high structural stability is achieved, but electrochemical inactivity results
Solution Approach 1:
The patent merges Li2MnO3 (structurally stable but electrochemically inactive) with LiMO2 (electrochemically active but less stable) in a composite structure. The Li2MnO3 component provides the stable framework while the LiMO2 component provides the electrochemical activity, allowing the cathode to exhibit both high structural stability and electrochemical activity simultaneously.
3Reliability
If solid solution of Li2MnO3 and LiMO2 is used, then electrochemical activity is achieved, but decomposition of electrolyte and gas generation at high voltage occur
Solution Approach 1:
The patent optimizes the composition parameters of the solid solution, specifically controlling the ratio of Li2MnO3 to LiMO2 and adjusting the lithium content to achieve a lithium molar fraction greater than 1. This parameter optimization allows the cathode to operate at high voltages (4.3V or higher) without causing electrolyte decomposition or gas generation, while maintaining electrochemical activity.
4Quantity of substance
If nickel-based lithium transition metal oxides are used, then high discharge capacity is achieved, but rapid phase transition and poor stability when exposed to air and moisture occur
Solution Approach 1:
The patent creates a composite material combining nickel-based lithium transition metal oxide (providing high discharge capacity) with Li2MnO3 (providing structural stability and resistance to phase transition). This composite structure maintains the high capacity characteristics of nickel-based materials while significantly improving their stability when exposed to air and moisture, and preventing rapid phase transition during cycling.
5Quantity of substance
If nickel-based lithium transition metal oxides operate at voltage of 4.3 V or higher, then high capacity is achieved, but rapid deterioration of cycle characteristics due to poor structural stability occurs
Solution Approach 1:
The patent changes the structural parameters of the cathode material by creating a solid solution with adjusted composition ratios and achieving a lithium molar fraction greater than 1. This parameter change strengthens the structural stability of the cathode, enabling it to operate at high voltages (4.3V or higher) without rapid deterioration of cycle characteristics, thus maintaining both high capacity and good cycle life.
Data Source
AI summary
Disclosed are a cathode active material for high voltage lithium secondary batteries and a lithium secondary battery including the same and, more particularly, the present invention relates to a cathode active material for lithium secondary batteries that includes a lithium transition metal oxide having a lithium molar fraction of greater than 1, containing a relative excess of nickel, and having a composition represented by Formula 1 below, wherein the lithium transition metal oxide has a Li2MnO3-like structure phase:Li1+aNibCocMn1−(a+b+c+d)MdO2-tAt (1)wherein 0.05≦a≦0.2, 0.4≦b≦0.7, 0.1≦c≦0.4, 0≦d≦0.1, and 0≦t<0.2;M is at least one divalent or trivalent metal; andA is at least one monovalent or divalent anion.