Cobalt-Coated Precursor for Lithium Battery Stability
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Solution Overview
Problem
Lithium secondary batteries face issues with high residual lithium on the surface of positive active materials, leading to swelling, reduced high-temperature stability, and capacity degradation due to unreacted LiOH or Li2CO3, which are exacerbated by water washing processes.
Innovation Solution
A method involving the production of a cobalt-coated precursor using a co-precipitation method with nickel-cobalt composite hydroxide, followed by cobalt coating and drying, to reduce unreacted lithium and enhance the positive active material's stability and capacity, involving steps like mixing metal compounds with aqueous ammonia and alkaline solutions, and heat-treating with lithium compounds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If water washing process is introduced to remove unreacted lithium, then residual lithium on surface is reduced, but capacity and efficiency characteristics are deteriorated and resistance increases during storage
Solution Approach 1:
The invention applies preliminary action by coating the precursor surface with cobalt before the water washing process. This cobalt coating is formed in advance to protect the precursor surface from damage during subsequent water washing, thereby preventing capacity degradation while still allowing effective removal of unreacted lithium
Solution Approach 2:
The cobalt coating acts as an intermediary layer between the precursor and the water washing process. This intermediate cobalt layer protects the precursor from direct contact with water that would cause surface damage, while still permitting the water to reach and remove unreacted lithium through the coating
2Reliability
If water washing process is introduced to remove unreacted lithium, then residual lithium on surface is reduced, but surface damages are generated on precursor
Solution Approach 1:
The cobalt coating is applied in advance before water washing to protect the precursor surface. This preliminary protective coating prevents mechanical and chemical damage to the precursor surface during the water washing process while still allowing the washing to effectively remove unreacted lithium
3Ease of operation
If LiOH is used as lithium compound for Ni rich system (65% or more Ni), then mixing is easier, but unreacted LiOH causes gelation during slurry mixing and high residual lithium on surface
Solution Approach 1:
The invention extracts and removes the harmful unreacted LiOH from the system through the water washing process. By washing the precursor surface after cobalt coating, the unreacted LiOH that causes gelation and residual lithium problems is effectively removed, while the cobalt coating protects the precursor during this extraction process
Solution Approach 2:
The invention changes the chemical composition parameter by coating with cobalt, which modifies the surface properties of the precursor. This cobalt coating changes how the surface interacts with water and unreacted LiOH, enabling effective removal of harmful substances while maintaining processingability
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 method results in a positive active material with improved high capacity, efficiency, and lifetime characteristics by reducing residual lithium, maintaining battery stability, and enhancing charge/discharge performance and resistance retention.
Implementation Method 1
mixing a metal mixed solution including a nickel-containing compound, a first cobalt-containing compound, a manganese-containing compound and a metal M, an aqueous ammonia solution as a complexing agent
Implementation Method 2
prepare a solution including a nickel-cobalt composite hydroxide represented by the following chemical formula 1 by a co-precipitation method
Implementation Method 3
an aqueous ammonia solution as a complexing agent, and a hydroxyl group-providing aqueous alkaline solution as a pH adjusting agent
Implementation Method 4
mixing the cobalt coating solution prepared in the step 2 with the solution including the nickel-cobalt composite hydroxide injected into the aqueous alkaline solution or distilled water to obtain a mixed solution, thereby coating a precursor with the mixed solution to coat cobalt on the precursor
Implementation Method 5
a step 5 of drying the separated cobalt-coated precursor
Data Source
AI summary
The present invention relates to a method of producing a cobalt-coated precursor, the cobalt-coated precursor produced by the method and a positive electrode active material for a lithium secondary battery, the positive electrode active material which is prepared using the cobalt-coated precursor and, more particularly, to a method of preparing a new positive electrode active material having improved high capacity and stability by coating cobalt on the surface of a precursor in the precursor step, thereby improving characteristics of the precursor degraded when washed with water, and a positive electrode active material prepared by the method.