Carbon Coated Lithium Transition Metal Phosphate for High Density Batteries
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Solution Overview
Problem
Existing lithium transition metal phosphate materials for secondary lithium ion batteries suffer from low electronic conductivity, limited Li+ diffusivity, and inhomogeneous carbon coatings, leading to reduced electrode density and capacity, which are inadequate for demanding applications such as electric vehicle batteries.
Innovation Solution
A particulate lithium transition metal phosphate with a homogeneous carbon coating deposited from a gas phase, using pyrolysis products of a carbon-containing compound, achieving a carbon content of less than 2.5 wt% and a powder press density increase of over 5%, resulting in higher electrode density and capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If carbon coating is deposited on lithium transition metal phosphate to improve electronic conductivity, then conductivity increases, but carbon distribution becomes inhomogeneous and particle sintering occurs
Solution Approach 1:
The patent applies preliminary action by coating the lithium transition metal phosphate particles with a polymeric carbon precursor solution before pyrolysis. This pre-coating step ensures uniform distribution of carbon precursor on particle surfaces, preventing inhomogeneous carbon deposition and sintering during subsequent high-temperature treatment. The polymeric coating acts as a protective layer that controls carbon formation in advance.
Solution Approach 2:
The patent uses a polymeric carbon precursor as an intermediary substance between the lithium transition metal phosphate particles and the final carbon coating. This intermediary allows controlled decomposition and uniform carbon deposition, mediating the transformation from bare particles to uniformly carbon-coated particles without direct harsh carbonization that would cause sintering.
2Reliability
If carbon content is increased to improve conductivity, then electrode density decreases and capacity is reduced
Solution Approach 1:
The patent applies parameter changes by precisely controlling the carbon content parameter to be less than 2.5 wt%, and preferably less than 1.5 wt%. This optimized carbon content parameter achieves sufficient electronic conductivity while minimizing the volume occupied by carbon, thereby maintaining high electrode density and battery capacity. The polymeric precursor decomposition also allows precise control of carbon deposition amount.
3Manufacturing precision
If polymeric carbon precursor is used to coat particles, then carbon deposit homogeneity improves, but severe sintering occurs during pyrolysis
Solution Approach 1:
The patent applies parameter changes by optimizing the pyrolysis temperature parameter to be between 400°C and 850°C, with preferred ranges of 500°C-750°C. This controlled temperature parameter ensures complete decomposition of the polymeric carbon precursor for homogeneous carbon coating, while avoiding excessive temperatures that would cause severe particle sintering and aggregation.
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 carbon-coated lithium transition metal phosphate exhibits increased powder press density, higher electrode density, and enhanced electrochemical properties, including improved energy density and current resistance, making it suitable for high-performance secondary lithium ion batteries.
Implementation Method 1
a homogeneous carbon coating which is deposited from the gas phase and which is present on the single particles, wherein the gas phase contains pyrolysis product of a carbon containing compound
Implementation Method 2
A carbon deposit can also be realized through a gas-phase reaction method as described in US 6,855,273 and US 6,962,666
Data Source
AI summary
The present invention relates to a particulate lithium transition metal phosphate with a homogeneous carbon coating deposited from the gas phase with as well as a process for its manufacture. The invention further relates the use of a carbon coated lithium transition metal phosphate as active material in an electrode, especially in a cathode.