Core-shell positive active material for lithium-ion battery stability
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Solution Overview
Problem
High nickel content in positive active materials for lithium-ion batteries leads to reduced structural and thermal stability, poor cycle performance, and increased gassing, due to the collapse of the layered structure and side reactions with the electrolyte, which affects the battery's safety and storage performance.
Innovation Solution
A core-shell structured positive active material is developed, where the inner core is a bulk-doped ternary material with a reduced mass concentration gradient of doping elements and a coating layer made of an oxide, optimizing the distribution and content of elements like Ni, Co, Mn, and doping elements to enhance stability and conductivity, and the coating layer prevents direct contact with the electrolyte, reducing side reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If nickel content in positive active material is increased to improve energy density, then energy density is improved, but structural stability and thermal stability deteriorate due to layered structure collapse and side reactions with electrolyte
Solution Approach 1:
The patent applies composite materials by creating a core-shell structure where the core is a high-nickel ternary material (NCM811) and the shell is an aluminum-containing coating layer. This composite structure allows the high-nickel core to provide high energy density while the aluminum-containing shell provides structural stability and prevents side reactions with the electrolyte, thus resolving the contradiction between energy density and structural stability.
Solution Approach 2:
The patent applies local quality by creating a concentration gradient of doping elements (Al, Ti, Zr) within the core particle, with higher concentrations at the surface and lower concentrations at the center. This local variation in composition allows the surface region to provide structural stability and protect against electrolyte reactions, while the nickel-rich core maintains high energy density.
2Quantity of substance
If nickel content is increased to improve energy density, then energy density is improved, but cycle performance deteriorates due to structural instability
Solution Approach 1:
The core-shell composite structure with aluminum-containing coating provides a stable framework that maintains structural integrity during repeated charging and discharging cycles, thereby improving cycle performance while preserving the high energy density of the nickel-rich core.
Solution Approach 2:
The concentration gradient of stabilizing elements (Al, Ti, Zr) with higher concentrations at the particle surface provides localized structural support where it is most needed during cycling, preventing structure collapse and maintaining cycle performance.
3Quantity of substance
If nickel content is increased to improve energy density, then energy density is improved, but gassing increases due to side reactions with electrolyte
Solution Approach 1:
The aluminum-containing coating layer acts as an intermediary barrier between the high-nickel ternary material and the electrolyte. This intermediate layer prevents direct contact and side reactions between the nickel-rich material and electrolyte, thereby reducing gassing while preserving the high energy density of the core material.
Solution Approach 2:
The composite core-shell structure isolates the reactive high-nickel core from the electrolyte through the stable aluminum-containing shell, preventing harmful side reactions that cause gassing while maintaining the energy density benefits of the nickel-rich composition.
4Manufacturing precision
If conventional coating methods are used to improve surface stability, then coating uniformity is improved, but energy consumption increases and lithium impurity content cannot be effectively reduced
Solution Approach 1:
The patent applies preliminary action by incorporating doping elements (Al, Ti, Zr) into the bulk structure of the NCM811 particles during the synthesis process, before the final coating step. This preliminary doping creates a stable framework that reduces the need for extensive subsequent coating and processing, thereby reducing energy consumption while achieving uniform distribution of stabilizing elements.
Solution Approach 2:
The concentration gradient distribution of doping elements is achieved through controlled synthesis conditions, creating local variations in composition that optimize both coating uniformity and energy efficiency. The gradient structure allows for reduced processing requirements compared to uniform high-concentration coatings.
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 results in a positive active material with high gram capacity, excellent cycle performance, and improved thermal stability, leading to enhanced storage and initial discharge capacity, while minimizing gassing and maintaining structural integrity during charging and discharging.
Implementation Method 1
the coating layer prevents direct contact with the electrolyte, reducing side reactions
Implementation Method 2
the inner core is a bulk-doped ternary material with a reduced mass concentration gradient of doping elements
Data Source
AI summary
This application provides a positive active material and a preparation method thereof, an electrochemical battery, a battery module, a battery pack, and an apparatus. The positive active material includes an inner core and a coating layer, where the coating layer coats a surface of the inner core. The inner core is selected from a ternary material with a molecular formula of Li1+a[NixCoyMnzMbM′c]O2−dYd, where distribution of each of the doping elements M, M′, and Y in the inner core meets the following condition: there is a reduced mass concentration gradient from an outer side of the inner core to a center of the inner core. The positive active material herein features high gram capacity, high structural stability, and high thermal stability, so that the electrochemical battery has excellent cycle performance and storage performance and high initial discharge gram capacity.