Core-Shell NCA Cathode Precursor for Volume-Change Buffering
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Solution Overview
Problem
Current NCA cathode materials for lithium-ion batteries face challenges such as poor cycling performance due to lithium-nickel disordering, high surface residual alkali content, and gas expansion, leading to irreversible capacity loss, primarily attributed to their compact internal structure and uneven volume changes during charge-discharge processes.
Innovation Solution
A nickel-cobalt-aluminum (NCA) cathode material precursor with a core-shell structure is developed, featuring a porous core with high nickel content to buffer volume changes and a low-nickel shell to alleviate structural stress, prepared through a method involving hydrothermal reactions and co-precipitation, where barium is used to create a porous core and a shell is formed through subsequent reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a compact internal structure is used to increase tap density, then energy density is improved, but volume change uniformity deteriorates leading to irreversible capacity loss
Solution Approach 1:
The patent introduces a porous hollow spherical core structure within the NCA cathode material particles. This porous core provides internal void space that can accommodate volume changes during lithium insertion and extraction, allowing the material to maintain its structural integrity over multiple cycles while still achieving high tap density through the spherical outer morphology.
Solution Approach 2:
The patent employs a nested structure where a porous hollow spherical core is embedded within a denser NCA material shell. This nested configuration allows the inner porous core to buffer volume changes while the outer shell maintains high density and active material content, resolving the contradiction between tap density and cycling stability.
2Quantity of substance
If high nickel content is used to increase reversible specific capacity, then energy density is improved, but structural stability deteriorates due to lithium-nickel disordering
Solution Approach 1:
The patent applies local quality by creating a compositional gradient where the core region contains very high nickel content (Ni0.95Co0.02Al0.03) for maximum capacity, while the shell region has reduced nickel content (Ni0.55Co0.2Al0.25) for enhanced structural stability. This spatial variation in composition allows the material to simultaneously achieve high reversible capacity and good cycling performance.
Solution Approach 2:
The patent creates a composite structure combining high-nickel carbonate hydroxide core material with low-nickel layered hydroxide shell material. This composite configuration leverages the high capacity of nickel-rich materials while the nickel-poor shell provides structural protection against degradation mechanisms such as lithium-nickel disordering and surface residue formation.
3Reliability
If aluminum doping is increased to improve structural stability, then cycling performance is improved, but reversible specific capacity decreases
Solution Approach 1:
The patent implements local quality by concentrating aluminum doping in the shell region (Ni0.55Co0.2Al0.25(OH)2.25) where it provides structural stabilization, while the core region maintains high nickel content (Ni0.95Co0.02Al0.03) for maximum capacity. This localized aluminum distribution allows the material to achieve both high reversible capacity and improved cycling stability without the trade-off inherent in uniform aluminum doping.
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 core-shell structure effectively mitigates volume changes during charge-discharge cycles, enhancing the cycling performance and reducing irreversible capacity loss, resulting in improved stability and retention of discharge capacity over multiple cycles.
Implementation Method 1
a first hydrothermal reaction to prepare a nickel-cobalt-aluminum-barium mixed precipitate, then barium is removed through a second hydrothermal reaction to obtain a nickel-cobalt-aluminum precipitate core
Implementation Method 2
S1: adding a soluble barium salt to a first nickel-cobalt-aluminum mixed solution to obtain a mixed metal solution, mixing the mixed metal solution with urea, and allowing a hydrothermal reaction
Implementation Method 3
mixing the mixed metal solution with urea, and allowing a hydrothermal reaction
Implementation Method 4
The precursor material prepared by the preparation method has an obvious loose core-shell structure with a high nickel content in the core, which can buffer a volume change during a charge-discharge process of a cathode material
Implementation Method 5
during a charge-discharge process of a cathode material
Data Source
AI summary
Disclosed in the present invention are an NCA positive electrode material precursor having a core-shell structure, a method for preparing same, and use thereof. The precursor is a spherical or spheroid particle and consists of an outer shell and an inner core. The outer shell has a chemical general formula of NiaCobAlc(OH)2+c, wherein a+b+c=1, 0.45≤a≤0.55, 0.15≤b≤0.25, and 0.25≤c≤0.35; the inner core has a chemical general formula of NixCoyAlz(CO3)1−z(OH)3z, wherein x+y+z=1, 0.85≤x<0.98, 0<y≤0.15, and 0<z≤0.15. The inner core has a porous structure. The inner core in the precursor of the present invention has a high nickel content and a porous structure, which can effectively buffer the volume change caused by subsequent charging and discharging of the NCA positive electrode material. The outer shell is a low-nickel material, which alleviates the volume change caused by the high nickel content.