Mixed Cathode Material for Lithium Battery Power Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Lithium secondary batteries face limitations in maintaining stable power and safety, particularly in low state of charge (SOC) ranges, due to rapid power decrease and high initial irreversible capacity when using traditional cathode materials like LiCoO2 and lithium manganese oxides, which can lead to structural instability and safety concerns.
Innovation Solution
A mixed cathode active material is developed by combining lithium manganese oxide with a second cathode active material, such as yMnO2 · (1-y)Li2MnO3, which has a plateau voltage profile between 2.5 V to 3.3 V, allowing additional lithium absorption and reducing initial irreversible capacity, along with the inclusion of conductive materials like graphite and conductive carbon to enhance conductivity and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If LiCoO2 is used to achieve high energy density, then capacity is improved, but structural stability deteriorates leading to safety issues at high temperature
Solution Approach 1:
The patent uses a composite cathode material consisting of LiCoO2 particles coated with a lithium manganese oxide layer (Li1-xMnxNi1-3yCoyO2). This composite structure combines the high capacity of LiCoO2 with the structural stability and safety of the manganese-rich spinel phase, preventing oxygen release and structural degradation at high temperatures while maintaining electrochemical performance.
2Stability of the object's composition
If lithium manganese oxide is used to improve safety, then structural stability is improved, but power characteristics deteriorate in low SOC range
Solution Approach 1:
The composite structure combines LiCoO2 cores (providing high power characteristics) with a spinel-phase lithium manganese oxide shell (providing structural stability). The spinel phase's three-dimensional lithium ion diffusion pathways maintain good power characteristics even in low SOC range, while the composite structure prevents the rapid resistance increase typical of pure lithium manganese oxide.
3Quantity of substance
If high voltage charging is used to increase energy density, then capacity is improved, but initial irreversible capacity increases
Solution Approach 1:
The patent optimizes the composition parameters of the spinel-phase coating layer (specifically the ratios of Li, Mn, Ni, and Co elements, controlled by parameters x and y) to achieve a balance between high voltage charging capability and minimal irreversible capacity. The controlled doping of Ni and Co into the spinel structure adjusts the electronic and ionic conductivity to reduce polarization effects during initial charging.
4Quantity of substance
If layered structure lithium manganese oxide is used to achieve high capacity, then capacity is improved, but safety limitations worsen
Solution Approach 1:
The patent utilizes the spinel crystal phase (as opposed to layered phase) for the lithium manganese oxide component, which exhibits superior structural stability and safety characteristics. The spinel phase prevents the Jahn-Teller distortion and oxygen release that plague layered structures at high voltages, while maintaining high lithium ion conductivity and capacity through its three-dimensional diffusion pathways.
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 mixed cathode active material provides a lithium secondary battery with a wide available SOC range, improved power characteristics, and enhanced safety by maintaining stable power and reducing voltage drops across the entire SOC range, making it suitable for applications in electric vehicles and plug-in hybrid electric vehicles.
Implementation Method 1
two lithium ions and two electrons are eliminated along with oxygen gas from Li2MnO3 constituting the layered structure lithium manganese oxide composite in a high voltage state of 4.5 V or more based on cathode potential during initial charge, but one lithium ion and one electron are only reversibly inserted into a cathode during discharge
Implementation Method 2
the inclusion of conductive materials like graphite and conductive carbon to enhance conductivity and stability
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Provided are a mixed cathode active material including layered structure lithium manganese oxide expressed as Chemical Formula 1 and a second cathode active material having a plateau voltage profile in a range of 2.5 V to 3.3 V, and a lithium secondary battery including the mixed cathode active material. The mixed cathode active material and the lithium secondary battery including the same may have improved safety and simultaneously, may be used in an operating device requiring the foregoing battery by widening a state of charge (SOC) range able to maintain power more than a required value by allowing the second cathode active material to complement low power in a low SOC range.