Engineering topics
Publications and source records attributed to Nyce, Michael.
Various zinc anodes with increasing calcium zincate (0%, 30%, 70%, 100%) were cycled at 50% theoretical Zn utilization to investigate cycle life and estimated cost. Failure mechanisms of majority 70% Zn/30% CaZn anodes are compared with pure CaZn.
Achieving high cycle life rechargeableγ-MnO 2 cathodes in alkaline batteries face many challenges. Chief among these is the inability of theγ-MnO 2 polymorph to retain its structural integrity when cycled to high utilization of its theoretical capacity ∼300 mAh g −1 . In this paper, we investigate the root cause of failure of MnO 2 cathodes under deep cycling in the one-electron discharge range and establish a strong link between capacity fade and the amount of birnessite formed. We uncover the underlying cause of failure by cycling industrial scaleγ-MnO 2 cathodes at various levels of theoretical capacity utilization (100%, 50%, and 30%) and in different KOH concentrations (37, 25, and 10 wt%). To determine materials evolution the cycled cathodes were dissected, characterized and analyzed using SEM, XRD, FIB/SEM, EIS, and XPS. Based on our findings, we propose that one major cause of failure of MnO 2 cathodes stems from the solubility of Mn +3 formed during discharge which effectively results in destruction of theγ-MnO 2 phase and amorphization of the cathode. The results show that the bulk of theγ-MnO 2 phase is preserved only in ∼10 wt% KOH, which indicates the attractive range of KOH concentration for cycling of rechargeableγ-MnO 2 cathodes.
In an embodiment, a secondary Zn—MnO 2 battery comprises a battery housing, a MnO 2 cathode, a Zn anode, and an electrolyte solution. The MnO 2 cathode, the Zn anode, and the electrolyte solution are disposed within the battery housing, and the MnO 2 cathode comprises a MnO 2 cathode mixture and a current collector. The MnO 2 cathode mixture is in electrical contact with at least a portion of an outer surface of the current collector, and the MnO 2 cathode has a porosity of from about 5 vol. % to about 90 vol. %, based on the total volume of the MnO 2 cathode mixture of the MnO 2 cathode.
Achieving commercially acceptable Zn-MnO2 rechargeable batteries depends on the reversibility of active zinc and manganese materials, and avoiding side reactions during the second electron reaction of MnO2. Typically, liquid electrolytes such as potassium hydroxide (KOH) are used for Zn-MnO2 rechargeable batteries. However, it is known that using liquid electrolytes causes the formation of electrochemically inactive materials, such as precipitation Mn3O4 or ZnMn2O4 resulting from the uncontrollable reaction of Mn3+ dissolved species with zincate ions. In this paper, hydrogel electrolytes are tested for MnO2 electrodes undergoing two-electron cycling. Improved cell safety is achieved because the hydrogel electrolyte is non-spillable, according to standards from the US Department of Transportation (DOT). The cycling of “half cells” with advanced-formulation MnO2 cathodes paired with commercial NiOOH electrodes is tested with hydrogel and a normal electrolyte, to detect changes to the zincate crossover and reaction from anode to cathode. These half cells achieved ≥700 cycles with 99% coulombic efficiency and 63% energy efficiency at C/3 rates based on the second electron capacity of MnO2. Other cycling tests with “full cells” of Zn anodes with the same MnO2 cathodes achieved ~300 cycles until reaching 50% capacity fade, a comparable performance to cells using liquid electrolyte. Electrodes dissected after cycling showed that the liquid electrolyte allowed Cu ions to migrate more than the hydrogel electrolyte. However, measurements of the Cu diffusion coefficient showed no difference between liquid and gel electrolytes; thus, it was hypothesized that the gel electrolytes reduced the occurrence of Cu short circuits by either (a) reducing electrode physical contact to the separator or (b) reducing electro-convective electrolyte transport that may be as important as diffusive transport.
Abstract not provided.
A method of operating a battery comprises discharging a cathode comprising manganese dioxide to within a 2nd electron capacity of the manganese dioxide at a C-rate of equal to or slower than C/10, recharging the battery, and cycling the battery during use a plurality of times. The cathode is in a battery, and the battery comprises the cathode, an anode, a separator disposed between the anode and the cathode, and an electrolyte. The cathode comprises the manganese dioxide and a conductive carbon. The anode comprises: a metal component and a conductive carbon. The metal component can be a metal, metal oxide, or metal hydroxide, and the metal of the metal component can be zinc, lithium, aluminum, magnesium, iron, cadmium and a combination thereof.
Abstract not provided.