Titanium-Separated Positive Electrode Layers for Deep-Charge Stability
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Solution Overview
Problem
Thin-film secondary batteries face challenges in charge and discharge characteristics, cycle performance, reliability, safety, and costs, particularly when the depth of charge exceeds 0.75, leading to breakdown of the positive electrode active material layer's crystal structure and reduced capacity.
Innovation Solution
A positive electrode for secondary batteries is designed with multiple active material layers and separation layers made of titanium compounds, alternately stacked to stabilize the crystal structure. The active material layers contain lithium, cobalt, and oxygen, with specific crystal plane orientations to enhance stability and performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If charging is performed with a depth of charge of 0.75 or more (lithium filling rate of 25% or less), then the charge capacity is improved, but the crystal structure of the positive electrode active material layer is broken and the charge and discharge capacity decreases
Solution Approach 1:
The positive electrode active material layer is divided into multiple thin layers (first, second, and third layers) with different compositions and functions. The first layer contains lithium cobalt oxide with specific crystal orientation, the second layer contains lithium nickel oxide with different crystal orientation, and the third layer contains lithium cobalt oxide again. This segmentation allows each layer to contribute differently to capacity while collectively maintaining structural stability during deep charging cycles.
Solution Approach 2:
The patent uses composite materials by combining different lithium transition metal oxides (lithium cobalt oxide and lithium nickel oxide) in a layered structure. Each material has distinct properties: lithium cobalt oxide provides high capacity and specific crystal orientation, while lithium nickel oxide provides complementary properties with different crystal orientation. This composite structure synergistically improves both charge capacity and structural stability during repeated deep charging cycles.
2Productivity
If the positive electrode active material layer is charged to high capacity (depth of charge ≥ 0.75), then the discharge capacity is improved, but the cycle performance deteriorates due to crystal structure breakdown
Solution Approach 1:
The positive electrode is segmented into three distinct layers with varying thicknesses and compositions. The first layer (30-70 nm thick) and third layer (30-70 nm thick) contain lithium cobalt oxide with (003) or (104) crystal orientation, while the middle second layer (70-130 nm thick) contains lithium nickel oxide with (200) or (220) crystal orientation. This segmentation enables the outer layers to provide high capacity while the middle layer provides structural buffering, maintaining cycle performance during high discharge capacity operation.
Solution Approach 2:
Different regions of the positive electrode are assigned different local qualities: the first and third layers have high lithium cobalt oxide content optimized for capacity, while the second layer has high lithium nickel oxide content optimized for structural stability. The crystal orientations are also locally optimized: (003) or (104) orientation in outer layers for capacity, and (200) or (220) orientation in the middle layer for stability. This local quality differentiation resolves the contradiction between high discharge capacity and cycle performance.
Data Source
AI summary
Provided is a positive electrode for a secondary battery, which has a small change in a crystal structure due to charging and discharging and has excellent cycle performance. The positive electrode for a secondary battery includes n positive electrode active material layers (n is an integer greater than or equal to 2), n−1 separation layer(s), and a positive electrode current collector layer. The positive electrode active material layers and the separation layer(s) are alternately stacked. The positive electrode active material layer contains lithium, cobalt, and oxygen. The separation layer contains a titanium compound. Titanium oxide and titanium nitride are preferable as the titanium compound, and titanium oxide is particularly preferable.