Lithium-ion Battery Cathode Charge Buffer for Pulse Overcharge
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Solution Overview
Problem
Current lithium-ion battery technologies face challenges in providing high-rate pulse overcharge protection, as state-of-the-art redox shuttles are limited by their solubility, diffusion coefficient, and charge transfer capabilities, which are insufficient for high-power applications like hybrid electric vehicles.
Innovation Solution
The design incorporates a charge buffer in the positive electrode with a redox shuttle, where the secondary material has a higher redox potential than the primary material, allowing it to store excess charge during high-rate pulse overcharging and discharge it through self-discharge, enhancing the battery's pulse overcharge protection capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a redox shuttle is incorporated into the electrolyte to provide overcharge protection, then the battery can operate safely below the redox potential, but the maximum shuttle current is limited by solubility and diffusion coefficient, making it insufficient for high-rate pulse overcharge protection
Solution Approach 1:
The positive electrode is segmented into two distinct materials: a primary material that operates at lower potential and a secondary material with higher redox potential that serves as a charge buffer. This segmentation allows the battery to handle high-rate pulse overcharge currents by distributing the charge acceptance between the two materials, with the secondary material accepting excess charge during pulse overcharge events.
Solution Approach 2:
The invention changes the electrochemical parameters of the positive electrode by introducing a secondary material with a higher redox potential than the redox shuttle. This parameter change enables the electrode to accept charges at higher potentials without triggering dangerous reactions, thereby increasing the maximum shuttle current capability while maintaining overcharge protection.
2Reliability
If the redox shuttle capacity is increased to handle higher overcharge currents, then overcharge protection is improved, but the solubility limit in non-aqueous electrolytes prevents achieving sufficient shuttle current for high-power applications
Solution Approach 1:
Instead of relying solely on increasing redox shuttle concentration, the invention segments the positive electrode into primary and secondary materials. The secondary material acts as an additional charge acceptance mechanism, effectively distributing the overcharge protection function between the redox shuttle and the secondary electrode material, thereby overcoming the solubility limit constraint.
Solution Approach 2:
The secondary positive electrode material serves as an intermediary charge buffer between the external charging source and the primary electrode materials. During pulse overcharge, this intermediary accepts excess charge that would otherwise overwhelm the redox shuttle, enabling the system to handle high-rate currents without exceeding the redox shuttle's solubility-based current limit.
3Reliability
If a charge buffer is added to the positive electrode to handle high-rate pulse currents, then pulse overcharge protection is enhanced, but the battery structure becomes more complex
Solution Approach 1:
The secondary positive electrode material serves multiple functions: it acts as a charge buffer during pulse overcharge events, contributes to the overall capacity of the battery, and maintains structural integrity of the electrode. This multi-functionality reduces the need for separate dedicated buffer components, thereby limiting the increase in device complexity.
Solution Approach 2:
The invention merges the charge buffer function with the primary positive electrode material by using a secondary material that is electrochemically integrated into the electrode structure. Rather than adding a separate physical buffer component, the charge buffer capability is combined with the electrode materials themselves, simplifying the overall device structure while achieving pulse overcharge protection.
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 design significantly improves the battery's ability to handle high-rate pulse overcharge currents, preventing dangerous voltage increases and enhancing safety by utilizing a charge buffer to complement the limitations of the redox shuttle.
Implementation Method 1
the redox shuttle can be reversibly electrochemically oxidized and reduced at a potential slightly higher than the working potential of the positive electrode of the battery
Implementation Method 2
the secondary material has a higher redox potential than the primary material, allowing it to store excess charge during high-rate pulse overcharging and discharge it through self-discharge
Data Source
AI summary
The present invention relates in general to the field of lithium rechargeable batteries, and more particularly relates to the positive electrode design of lithium-ion batteries with improved high-rate pulse overcharge protection. Thus the present invention provides electrochemical devices containing a cathode comprising at least one primary positive material and at least one secondary positive material; an anode; and a non-aqueous electrolyte comprising a redox shuttle additive; wherein the redox potential of the redox shuttle additive is greater than the redox potential of the primary positive material; the redox potential of the redox shuttle additive is lower than the redox potential of the secondary positive material; and the redox shuttle additive is stable at least up to the redox potential of the secondary positive material.