Bimodal Cathode Composition for Silicon-Anode Lithium Loss
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Solution Overview
Problem
Lithium secondary batteries face challenges with high irreversible capacity loss from negative electrode materials, leading to reduced battery performance and increased lithium consumption, and existing positive electrode materials are expensive and generate excessive lithium by-products.
Innovation Solution
A method involving a bimodal particle diameter distribution positive electrode material, comprising a small particle lithium composite transition metal oxide with a boron-containing coating and a large particle lithium composite transition metal oxide with a cobalt and boron-containing coating, is used to compensate for irreversible capacity loss and reduce lithium consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If non-carbon-based negative electrode materials (silicon, tin, oxides) are used to achieve high capacity, then capacity per unit mass is improved, but irreversible capacity loss during initial charge and discharge increases
Solution Approach 1:
The positive electrode is segmented into two distinct active materials with different particle sizes and compositions: small particle lithium nickel-based oxide (D50 < 7 μm) and large particle lithium nickel-based oxide (D50 ≥ 8 μm). This segmentation allows each particle size to fulfill different functional roles in compensating for irreversible capacity loss.
Solution Approach 2:
Different regions of the positive electrode material have different compositions and properties. The small particles provide one type of local quality (higher surface area for rapid lithium insertion/extraction), while large particles provide another (lower surface area for structural stability), collectively addressing the irreversible capacity loss problem.
2Reliability
If lithium nickel-based oxide is used as positive electrode material to compensate for irreversible capacity loss, then negative electrode performance is improved, but cost increases and lithium by-products generation increases
Solution Approach 1:
The invention changes multiple parameters of the lithium nickel-based oxide: particle size (bimodal distribution with D50 < 7 μm and D50 ≥ 8 μm), composition (Li1+x(Ni1-y-zMn yCo z)O2 with specific ranges: 0 < x ≤ 0.2, 0.3 ≤ 1-y-z ≤ 0.8, 0 < y ≤ 0.5, 0 < z ≤ 0.5), and surface treatment (coating layer). These parameter changes optimize performance while controlling lithium by-products.
Solution Approach 2:
The positive electrode uses a composite material system combining lithium nickel-based oxide with specific ratios of small and large particles, creating a synergistic effect that improves negative electrode performance while managing lithium consumption and by-products generation.
3Ease of manufacture
If uniform particle size positive electrode material is used, then manufacturing is simplified, but performance optimization is limited
Solution Approach 1:
The positive electrode material is segmented into two particle size ranges (small particles with D50 < 7 μm and large particles with D50 ≥ 8 μm) that can be separately prepared and then mixed, maintaining manufacturing simplicity while achieving superior performance through the synergistic effects of different particle sizes.
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 improves output characteristics and high-temperature lifetime of lithium secondary batteries by reducing lithium ion loss and increasing energy density while minimizing resistance and lithium consumption.
Implementation Method 1
a boron-containing coating layer formed on the small particle lithium composite transition metal oxide
Implementation Method 2
a cobalt and boron-containing coating layer formed on the large particle lithium composite transition metal oxide
Implementation Method 3
performing a heat treatment
Data Source
AI summary
A method of preparing a lithium secondary battery includes:(1) mixing a small particle lithium composite transition metal oxide having an average particle diameter (D50) of less than 7 μm with a boron-containing raw material and performing a heat treatment, mixing a large particle lithium composite transition metal oxide having an average particle diameter (D50) of 8 μm or more with a cobalt-containing raw material and a boron-containing raw material and performing a heat treatment,mixing the first positive electrode active material and the second positive electrode active material to prepare a positive electrode material having a bimodal particle diameter distribution, preparing a positive electrode by coating the positive electrode material on a positive electrode collector, and assembling the positive electrode, a negative electrode including a silicon-based negative electrode active material, and a separator.