Magnesium-Substituted Cobalt Oxide for High-Voltage Battery Stability
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Solution Overview
Problem
High-potential charging in nonaqueous electrolyte secondary batteries destabilizes the crystal structure of the positive electrode active material, leading to reduced charge/discharge cycle stability when magnesium is abstracted at potentials above 4.33 V, causing structural disruptions and phase transitions.
Innovation Solution
A nonaqueous electrolyte secondary battery with a positive electrode active material of Li1-aMgaCo1-bMbO2, where 0<a≤0.05 and 0≤b≤0.1, incorporating magnesium in the lithium layer and cobalt composite oxide, with nickel, manganese, and aluminum substitution to stabilize the crystal structure, and a rare-earth compound or oxide attached to the surface to suppress structural changes, along with a magnesium-containing compound on the negative electrode to form a protective film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If charge voltage is increased to 4.33 V or more versus lithium, then battery capacity is improved, but crystal structure of positive electrode active material is destabilized and charge/discharge cycle is reduced
Solution Approach 1:
Magnesium is substituted into the lithium layer of the positive electrode active material before high-potential charging is performed. This preliminary substitution creates a stabilized crystal structure that can withstand the high charge voltage of 4.33 V or more without undergoing detrimental phase transitions, thereby enabling both high capacity and long cycle life
2Stability of the object's composition
If magnesium is substituted in lithium layer at 4.3 V or less, then lithium layer is stabilized, but magnesium is entirely abstracted at higher potential and crystal structure becomes destabilized
Solution Approach 1:
The charge voltage parameter is increased to 4.33 V or more versus lithium, which changes the electrochemical environment to prevent complete magnesium abstraction. This parameter change, combined with the magnesium substitution, maintains magnesium presence in the lithium layer at high voltage, stabilizing the crystal structure
3Quantity of substance
If cobalt is partially substituted with nickel, then high capacity is achieved, but crystal structure stability may be compromised
Solution Approach 1:
The positive electrode active material is designed as a composite with multiple elements: lithium, magnesium, cobalt, nickel, manganese, and aluminum. This composite structure combines the high capacity contribution of nickel substitution with the structural stabilization provided by magnesium in the lithium layer and manganese/aluminum in the transition metal layer, achieving both high capacity and 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 solution stabilizes the crystal structure and enhances charge/discharge cycle characteristics even at high potentials, suppressing structural changes and degradation of the negative electrode, resulting in a long-life battery with improved capacity retention at high charge voltages.
Implementation Method 1
magnesium is present in the lithium layer after charge is performed at a potential of 4.53 V or more versus lithium... the crystal structure of the positive electrode active material is likely to be deteriorated... magnesium in the lithium layer is entirely abstracted and there is a problem in that the crystal structure is destabilized
Implementation Method 2
4.5 mole percent to 10 mole percent of a magnesium-containing compound is present on the negative electrode with respect to magnesium in the positive electrode... suppress the degradation of the negative electrode
Implementation Method 3
a positive electrode containing a positive electrode active material storing and releasing lithium ions, a negative electrode containing a negative electrode active material storing and releasing lithium ions
Data Source
AI summary
Provided is a nonaqueous electrolyte secondary battery in which the structural change of a positive electrode active material is suppressed at high voltage and which can achieve high capacity and long life. The nonaqueous electrolyte secondary battery includes a positive electrode containing a positive electrode active material storing and releasing lithium ions, a negative electrode containing a negative electrode active material storing and releasing lithium ions, and a nonaqueous electrolyte. The positive electrode active material is a cobalt composite oxide which has a layered rock salt structure and which includes a lithium layer containing magnesium, magnesium is present in the lithium layer after charge is performed at a potential of 4.53 V or more versus lithium, and 4.5 mole percent to 10 mole percent of a magnesium-containing compound is present on the negative electrode with respect to magnesium in the positive electrode.