Lithium-Nickel-Cobalt-Manganese Oxide Pre-Firing for High Li Occupancy
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Solution Overview
Problem
The synthesis of lithium-nickel-cobalt-manganese complex oxides with high lithium occupancy is challenging due to difficulties in achieving a dense crystal structure and stoichiometric composition, particularly at high nickel molar ratios, where low-temperature firing limits lithium ion diffusion and high-temperature firing accelerates crystal growth before uniform diffusion of starting materials.
Innovation Solution
A method involving pre-firing the starting source material at a temperature lower than 800°C, higher than the melting point of the lithium supply source, followed by further firing to enhance lithium ion diffusion and achieve a high Li occupancy and crystallinity, with a molar composition ratio of lithium to other elements between 1 and 1.2, and using lithium carbonate or hydroxide as the lithium supply source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If low-temperature firing is used, then energy consumption is reduced and crystal growth is controlled, but lithium ion diffusion is impeded and Li occupancy remains low
Solution Approach 1:
The patent applies preliminary action by conducting a pre-firing step before the main firing process. The pre-firing at lower temperature (below 800°C) prepares the starting materials by initiating partial decomposition and creating a more reactive state, which then facilitates better lithium ion diffusion during the subsequent main firing step, ultimately achieving high Li occupancy without excessive energy consumption
2Manufacturing precision
If high-temperature firing is used, then lithium ion diffusion is enhanced and Li occupancy increases, but crystal growth accelerates and uniform diffusion of starting materials is compromised
Solution Approach 1:
The patent applies segmentation by dividing the firing process into two distinct stages: pre-firing at lower temperature to prepare starting materials and initiate controlled reactions, followed by main firing at higher temperature to achieve complete reaction and high Li occupancy. This segmented approach prevents premature crystal growth while ensuring uniform diffusion and high lithium occupancy in the final product
3Quantity of substance
If high nickel molar ratio is used, then energy density is improved, but lithium ion diffusion is impeded and Li occupancy decreases
Solution Approach 1:
The patent applies parameter changes by optimizing the firing temperature profile (pre-firing below 800°C followed by main firing at higher temperature) and controlling the duration of each stage. These parameter adjustments create optimal conditions for lithium ion diffusion even in high-nickel compositions, enabling both high energy density and high Li occupancy to be achieved simultaneously
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 method produces lithium-nickel-cobalt-manganese complex oxides with a lamellar structure and high Li occupancy (>96.5%), resulting in improved battery characteristics such as battery capacity, cycle stability, and high-rate performance.
Implementation Method 1
a temperature lower than 800° C. and higher than a melting temperature of the lithium supply source
Implementation Method 2
diffusion of lithium ions in solid is impeded and it is desirable to increase the Li occupancy
Data Source
AI summary
The present invention discloses a method for producing a positive electrode active material for a lithium secondary battery constituted by a lithium-nickel-cobalt-manganese complex oxide with a lamellar structure, the method including: (1) a step of preparing a starting source material for producing the complex oxide including a lithium supply source, a nickel supply source, a cobalt supply source, and a manganese supply source; (2) a step of pre-firing the starting source material by heating at a pre-firing temperature that has been set to a temperature lower than 800° C. and higher than a melting temperature of the lithium supply source; and (3) a step of firing the pre-fired material obtained in the pre-firing step by raising a temperature to a temperature range higher than the pre-firing temperature.