Cobalt Gradient Positive Electrode Active Material for Low SOC Output
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries face challenges in achieving high output characteristics, particularly at low state-of-charge (SOC), due to limitations in the structure and composition of positive electrode active materials, which affect the battery's performance and stability.
Innovation Solution
A positive electrode active material is developed with secondary particles having a smoothness greater than 0.73 and circularity greater than 0.83, composed of lithium transition metal composite oxide with a layered structure, containing nickel and cobalt, where a higher cobalt concentration is maintained near the surface, enhancing the contact area and reducing resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a coating layer containing Co is disposed on the surface of the positive electrode active material, then storage stability (weather resistance) is improved, but the output characteristics at low SOC are not sufficiently enhanced
Solution Approach 1:
The patent applies local quality by creating a cobalt concentration gradient within the particle structure, where the second region (outer layer) has higher cobalt content than the first region (inner layer). This spatial differentiation allows the outer surface to provide storage stability while the overall structure maintains output characteristics, resolving the contradiction between these two performance aspects.
2Power
If secondary particles are formed by aggregation of primary particles to achieve high output characteristics, then battery capacity increases, but the particle structure complexity increases making uniform coating difficult
Solution Approach 1:
The patent changes the compositional parameter by creating a cobalt concentration gradient between the first and second regions of the secondary particles. This parameter change allows uniform coating formation on the aggregated particle structure while maintaining the high capacity benefits of secondary particle morphology, thus resolving the contradiction between capacity and coating uniformity.
3Power
If the cobalt compound is adhered to the positive electrode active material raw material, then the cobalt concentration near the surface increases improving output characteristics, but the manufacturing process complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-forming the cobalt compound adhesion on the positive electrode active material raw material before final electrode fabrication. This preliminary coating step establishes the desired cobalt concentration gradient in advance, simplifying subsequent manufacturing processes while achieving the target output characteristics at low SOC.
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 improved structure and composition of the positive electrode active material enhance the output characteristics at low SOC by reducing interfacial resistance and improving the uniform adhesion of cobalt, leading to better battery performance and stability.
Implementation Method 1
bringing the positive electrode active material raw material into contact with a cobalt compound to obtain a cobalt-adhered material in which the cobalt compound is adhered to the positive electrode active material raw material
Implementation Method 2
heat-treating the cobalt-adhered material at a temperature of 500° C. or greater and lower than 1100° C. to obtain a heat-treated material
Data Source
AI summary
The positive electrode active material includes secondary particles formed by aggregation of a plurality of primary particles that contain a lithium transition metal composite oxide having a layered structure and containing lithium and nickel. The secondary particles have a smoothness greater than 0.73, and a circularity greater than 0.83. The secondary particles contain cobalt and have a first region at a depth of 150 nm from a surface of the respective secondary particle and a second region at a depth of 10 nm or less from the surface of the respective secondary particle, and a ratio of a number of moles of cobalt to a total number of moles of metal elements other than lithium in the second region is larger than a ratio of a number of moles of cobalt to a total number of moles of metal elements other than lithium in the first region.