Lithium-Transition Metal Composite Cathode for High-Rate Battery Performance
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Solution Overview
Problem
Conventional cathode active materials for lithium secondary batteries face challenges such as high cost, limited lifespan, and poor high-rate charge/discharge characteristics due to instability and phase changes, particularly with lithium cobalt oxides and lithium nickel oxides, while lithium manganese oxides have low capacity and conductivity issues.
Innovation Solution
A lithium-transition metal composite oxide with a specific composition, including excess lithium and nickel with an oxidation number of at least 2, along with manganese and cobalt, is used to maintain a stable crystal structure and enhance rate characteristics by controlling the average oxidation number of transition metals and adjusting molar ratios to ensure lithium ion mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lithium cobalt oxide (LiCoO2) is used as cathode active material, then excellent lifespan and charge/discharge efficiency are achieved, but cost increases significantly due to expensive cobalt
Solution Approach 1:
The patent uses a composite oxide material with formula Li1+aNi1/2-bMn1/2+bO2, combining nickel and manganese in specific ratios within a lithium oxide matrix. This composite approach achieves the desired performance while controlling cost by optimizing the mix of expensive (nickel) and inexpensive (manganese) transition metals.
Solution Approach 2:
The patent systematically varies compositional parameters (a, b values representing lithium excess and nickel-manganese ratio) to optimize performance. By changing these parameters, the material achieves excellent lifespan and efficiency comparable to LiCoO2 while using cheaper nickel-manganese composition.
2Quantity of substance
If lithium nickel oxide (LiNiO2) is used to reduce cost and increase discharge capacity, then cost and capacity improve, but crystal structure stability deteriorates due to phase transfer under charge/discharge cycles
Solution Approach 1:
The patent creates a composite oxide Li1+aNi1/2-bMn1/2+bO2 that combines nickel (providing high capacity) with manganese (providing structural stability). The synergistic combination allows the material to maintain crystal structure stability while achieving high discharge capacity comparable to pure lithium nickel oxide.
Solution Approach 2:
The patent optimizes the local composition by controlling the nickel-to-manganese ratio parameter (b) to create specific regions with different properties. This allows high-capacity nickel-rich regions coexist with stability-providing manganese-rich regions within the same crystal structure.
3Temperature
If lithium manganese oxide (LiMnO2 or LiMn2O4) is used to achieve low cost and excellent thermal stability, then cost and thermal stability improve, but discharge capacity and conductivity decrease
Solution Approach 1:
The patent develops a composite oxide Li1+aNi1/2-bMn1/2+bO2 that integrates manganese (providing thermal stability) with nickel (providing high capacity and conductivity). The composite structure allows the material to simultaneously achieve excellent thermal stability and high discharge capacity with good conductivity.
Solution Approach 2:
The patent optimizes compositional parameters to balance thermal stability and performance. By adjusting the nickel-manganese ratio and lithium excess parameter, the material achieves optimal combination of thermal stability, discharge capacity, and conductivity that surpasses conventional lithium manganese oxides.
4Reliability
If excess lithium is added to improve rate characteristics and maintain stable crystal structure, then rate characteristics and structural stability improve, but manufacturing precision requirements increase
Solution Approach 1:
The patent defines specific parameter ranges (0 < a ≤ 0.4 and 0 < b ≤ 0.25) that guarantee optimal performance. These quantified parameters provide clear manufacturing targets, making it easier to control composition within acceptable tolerances while achieving excellent rate characteristics and structural stability.
Solution Approach 2:
The patent intentionally adds excess lithium (parameter a) beyond stoichiometric requirements to ensure complete occupation of lithium sites and maintain structural stability during cycling. This deliberate excess compensates for potential lithium loss during manufacturing and cycling, ensuring consistent performance.
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 solution provides a cathode active material with improved stability and enhanced rate characteristics under high-rate charge/discharge conditions, maintaining a stable crystal structure and increasing the coulombic force between transition metals and oxygen, resulting in superior performance compared to conventional materials.
Implementation Method 1
increasing the coulombic force between transition metals and oxygen
Implementation Method 2
lithium-transition metal composite oxide... stable crystal structure
Implementation Method 3
ensure lithium ion mobility
Data Source
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AI summary
Provided is a cathode active material for a lithium secondary battery, including a lithium-transition metal composite oxide represented by the following formula (1), which contains an excess of lithium, so as to exhibit enhanced rate characteristics under high rate charge/discharge conditions: Lii+aNi'bNi"cMndCoeO2 (1) wherein each of a, b, c, d and e has the same meaning as defined in the disclosure. The cathode active material according to the present invention includes an excess of lithium and, different from conventional technologies, a lithium-transition metal composite oxide containing a nickel element with a predetermined oxidation number, so that the active material exhibits a stable crystal structure and excellent rate characteristics under high rate charge/discharge conditions.