Cathode Active Material Layer Orientation Control via Low-Temperature PVD
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Solution Overview
Problem
The existing methods for forming cathode active material layers in lithium batteries, such as the PVD method, lead to impurity formation, surface cracking, and increased resistance due to high-temperature substrate heating, resulting in decreased battery capacity and output.
Innovation Solution
A method involving physical vapor deposition at a substrate temperature of 300° C. or less, followed by an annealing treatment at a crystallizable temperature, using a substrate with orientation properties to control the crystal structure and incline the 'c' axis of LiXaOb against the normal line, thereby reducing impurities and enhancing film flatness and conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the substrate is heated to high temperature during film formation, then the lithium complex oxide film can be crystallized, but Li is evaporated easily and lost more than stoichiometric ratio producing impurities such as Co3O4
Solution Approach 1:
The process is divided into two separate stages: (1) film formation at low temperature (300°C or less) to deposit the cathode active material precursor film without Li evaporation, and (2) subsequent annealing treatment at high temperature to crystallize the film. This segmentation allows crystallization without Li loss during the sensitive deposition phase.
Solution Approach 2:
The precursor film is formed first at low temperature with the correct stoichiometry, preparing the material in advance for crystallization. The Li content is preserved during deposition, and then crystallization is achieved in the second stage without further Li evaporation.
2Stability of the object's composition
If the substrate is heated to high temperature during film formation, then the lithium complex oxide film can be crystallized, but the obtained cathode active material layer causes cracks on surface after annealing treatment and is inferior in surface flatness
Solution Approach 1:
The process separates film formation and crystallization into distinct stages. The precursor film is deposited at low temperature ensuring good surface flatness and adhesion, then crystallized through annealing without causing surface cracking, as the low-temperature deposition creates a more resilient base structure.
3Ease of manufacture
If a PVD method such as sputtering method is used, then the cathode active material layer can be formed, but it is difficult to perform orientation control and the obtained cathode active material layer increases in resistance
Solution Approach 1:
The invention changes the substrate temperature parameter during deposition (maintaining 300°C or less) and controls the annealing temperature and atmosphere parameters to achieve preferred crystal orientation. This parameter control enables orientation control without changing the PVD manufacturing method itself.
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
This approach results in a high-purity cathode active material layer with improved flatness and reduced resistance, enabling a large-capacity and high-output all solid lithium secondary battery.
Implementation Method 1
forming a cathode active material precursor-film on the substrate by a physical vapor deposition method
Implementation Method 2
performing an annealing treatment for the cathode active material precursor-film at a temperature of a crystallizable temperature of the LiXaOb or more
Implementation Method 3
the heating of a substrate to high temperature during film formation allows a crystallized lithium complex oxide film
Data Source
AI summary
The main object of the present invention is to provide a method for producing a cathode active material layer, which allows a high-purity lithium complex oxide by restraining impurities from being produced, allows a flat film, and allows orientation control. The present invention solves the above-mentioned problems by providing a method for producing a cathode active material layer, in which a cathode active material layer is formed on a substrate and contains LiXaOb (X is a transition metal element of at least one kind selected from the group consisting of Co, Ni and Mn, a=0.7-1.3, and b=1.5-2.5), characterized in that the method comprises the steps of: forming a cathode active material precursor-film on the above-mentioned substrate by a physical vapor deposition method while setting a temperature of the substrate at 300° C. or less, and performing an annealing treatment for the cathode active material precursor-film at a temperature of a crystallizable temperature of the LiXaOb or more, and characterized in that the substrate has orientation property in a surface.