Nickel Hydrogen Battery Lithium Stabilization
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Solution Overview
Problem
Conventional nickel hydrogen secondary batteries face challenges in achieving high-rate dischargeability while maintaining cycle life properties due to the reduction in alkaline electrolyte and increased internal resistance, leading to reduced capacity and corrosion of the hydrogen storage alloy.
Innovation Solution
A nickel hydrogen secondary battery configuration with a specific amount of Li (15-50 mg/Ah) and rare earth-Mg—Ni-based hydrogen storage alloy particles coated with rare earth hydroxide, along with a conductive layer on the positive electrode active material, helps maintain alkaline electrolyte levels and enhances corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lithium is added to the positive electrode to improve cycle life properties, then the conductive network is stabilized and cobalt compound reduction is suppressed, but the alkaline electrolyte is incorporated into the positive electrode, reducing the electrolyte amount in the separator and increasing internal resistance
Solution Approach 1:
The patent optimizes the lithium content parameter within a specific range (0.01-5 mass% of the positive electrode active material) to balance two opposing effects: sufficient lithium to stabilize the conductive network and suppress cobalt reduction, but limited lithium to prevent excessive electrolyte incorporation. This parameter optimization resolves the contradiction by finding the optimal point where cycle life improvement is achieved while internal resistance increase is minimized.
2Power
If the discharge rate is increased to meet higher power consumption requirements, then the power output is improved, but the corrosion reaction of the hydrogen storage alloy accelerates and alkaline electrolyte is consumed, reducing cycle life properties
Solution Approach 1:
The patent applies prior cushioning by adding lithium to the positive electrode before operation, which preemptively stabilizes the conductive network and suppresses cobalt compound reduction. This pre-protection mechanism creates a more stable chemical environment that resists corrosion reactions even when the battery operates at high discharge rates, thereby cushioning against the accelerated degradation that would normally occur under high power conditions.
3Quantity of substance
If the capacity is increased by improving the utilization factor of positive electrode active material through cobalt compound conductive network formation, then the battery capacity increases, but the cobalt compound is reduced and eluted during charge-discharge cycles, destroying the conductive network
Solution Approach 1:
The patent introduces lithium as an intermediary substance that mediates between the cobalt compound conductive network and the alkaline electrolyte. The lithium stabilizes the cobalt compound, preventing its reduction and elution during charge-discharge cycles. This intermediary action allows the cobalt conductive network to maintain its structural integrity and high conductivity over many cycles, enabling sustained high capacity without conductive network destruction.
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 configuration improves high-rate dischargeability and cycle life properties by preventing conductive network destruction and reducing alkaline electrolyte consumption, thus maintaining low internal resistance and extending battery life.
Implementation Method 1
The lithium hydroxide or lithium stabilizes the cobalt compound forming a conductive network and suppresses the reduction in the valence of the cobalt compound and the reduction/elution reaction associated with the charge-discharge cycle
Implementation Method 2
The presence of lithium in a positive electrode, however, allows an alkaline electrolyte to be incorporated into a layer between crystals of nickel hydroxide
Implementation Method 3
the hydrogen storage alloy particles include, on the surface thereof, a rare earth hydroxide which is the hydroxide of the rare earth element
Implementation Method 4
a conductive network of a cobalt compound with high conductivity is formed on the surface of nickel hydroxide particles as positive electrode active material
Data Source
AI summary
A nickel hydrogen secondary battery accommodates an electrode group including a positive electrode and a negative electrode which are stacked one on top of another through a separator, together with an alkaline electrolyte. The battery contains Li, with a total amount of Li in the battery 2 of 15 to 50 mg/Ah, as determined as the mass in terms of LiOH per Ah of the positive electrode capacity. The negative electrode includes particles of rare earth-Mg—Ni-based hydrogen storage alloy which contains a rare earth element, Mg and Ni. The hydrogen storage alloy particles 44 includes, on the surface thereof, a rare earth hydroxide which is the hydroxide of a rare earth element and has a specific surface area of 0.1 to 0.5 m2/g.