Ni-Gradient NMC Cathode Composition for Low Irreversible Capacity
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Solution Overview
Problem
Rechargeable lithium ion batteries face limitations in reversible capacity and cycle stability due to high irreversible capacity (IRRQ) in positive electrode materials, which restricts the utilization of negative electrode materials and decreases power performance at the end of discharge.
Innovation Solution
A powderous positive electrode material with a specific composition and crystallite size range, including a lithium transition metal-based oxide formula Li1+a ((Niz (Ni0.5Mn0.5)y Cox)1−k Ak), where A is a dopant, and a molar ratio gradient of Ni across the particle, is developed, along with a double sintering method to achieve low IRRQ and improved electrochemical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If NMC materials with high Ni-excess are used to increase reversible capacity, then the theoretical capacity increases, but the irreversible capacity (IRRQ) also increases
Solution Approach 1:
The patent applies local quality by creating a compositional gradient within the NMC particles, where the surface region has different Ni content compared to the core. This gradient structure allows the surface to have lower Ni-excess (reducing IRRQ) while the core maintains high Ni-excess (providing high reversible capacity), thus resolving the contradiction between increasing capacity and minimizing energy loss.
Solution Approach 2:
The patent effectively creates a composite structure with varying Ni content across the particle, combining regions of high Ni-excess and low Ni-excess within a single material system. This composite approach enables simultaneous achievement of high reversible capacity from the Ni-rich core and low irreversible capacity from the Ni-poor surface.
2Quantity of substance
If high Ni-excess NMC materials are used to increase capacity, then the charge capacity increases, but the utilization of negative electrode material decreases
Solution Approach 1:
By implementing a Ni concentration gradient from core to surface, the patent creates local regions with different electrochemical properties. The surface region with lower Ni-excess provides better voltage matching with the negative electrode, improving utilization, while the core maintains high capacity potential.
3Ease of manufacture
If conventional sintering methods are used, then the material can be produced, but the crystallite size is large leading to high IRRQ
Solution Approach 1:
The patent applies parameter changes by precisely controlling sintering temperature (750-850°C) and time (4-24 hours) to achieve optimal crystallite size in the 20-40 nm range. This parameter optimization reduces IRRQ while maintaining production feasibility through a controlled thermal process.
Solution Approach 2:
The patent employs a two-stage sintering process where a preliminary sintering step prepares the material structure before the final sintering step. This preliminary action allows better control over crystallite growth and composition distribution, resulting in smaller crystallite size and reduced IRRQ.
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 enhances reversible capacity, balances capacity between positive and negative electrodes, and improves power performance and cycle stability by reducing IRRQ, leading to better battery performance and longer cycle life.
Implementation Method 1
The electrochemical performance of positive electrode materials depends on the reversible and irreversible chemical reaction in a battery
Implementation Method 2
a double sintering method to achieve low IRRQ and improved electrochemical properties
Data Source
AI summary
A powderous positive electrode material for lithium ion batteries, comprising crystalline lithium transition metal-based oxide particles having a general formula Li1+a ((Niz (Ni0.5Mn0.5)y Cox)1−k Ak)1−a O2, wherein A is a dopant, −0.030≤a≤0.025, 0.10≤x≤0.40, 0.25≤z≤0.52, x+y+z=1 and k≤0.01, wherein the crystalline powder has a crystallite size less than 33 nm as determined by the Scherrer equation based on the peak of the (104) plane obtained from the X-ray diffraction pattern using a Cu K α radiation source, and wherein the molar ratio MR(Ni) of Ni versus the total transition metal content in a cross section of a particle is higher in the surface area than in the center area of the particle, as determined by EDS analysis.