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Title: Operando identification of the point of [Mn- 2]O- 4 spinel formation during gamma-MnO 2 discharge within batteries

The rechargeability of γ-MnO 2 cathodes in alkaline batteries is limited by the formation of the [Mn 2]O 4 spinels ZnMn 2O 4 (hetaerolite) and Mn 3O 4 (hausmannite). However, the time and formation mechanisms of these spinels are not well understood. Here we directly observe γ-MnO 2 discharge at a range of reaction extents distributed across a thick porous electrode. Coupled with a battery model, this reveals that spinel formation occurs at a precise and predictable point in the reaction, regardless of reaction rate. Observation is accomplished by energy dispersive X-ray diffraction (EDXRD) using photons of high energy and high flux, which penetrate the cell and provide diffraction data as a function of location and time. After insertion of 0.79 protons per γ-MnO 2 the α-MnOOH phase forms rapidly. α-MnOOH is the precursor to spinel, which closely follows. ZnMn 2O 4 and Mn 3O 4 form at the same discharge depth, by the same mechanism. The results show the final discharge product, Mn 3O 4 or Mn(OH) 2, is not an intrinsic property of γ-MnO 2. While several studies have identified Mn(OH) 2 as the final γ-MnO 2 discharge product, we observe direct conversion to Mn 3O 4 withmore » no Mn(OH) 2.« less
 [1] ;  [2] ;  [3] ;  [4] ;  [1] ;  [1] ;  [2] ;  [3] ;  [1]
  1. City College of New York, NY (United States)
  2. Princeton Univ., NJ (United States)
  3. Brookhaven National Lab. (BNL), Upton, NY (United States)
  4. Rutgers Univ., Piscataway, NJ (United States)
Publication Date:
Report Number(s):
Journal ID: ISSN 0378-7753
Grant/Contract Number:
SC00112704; AC02-98CH10886
Accepted Manuscript
Journal Name:
Journal of Power Sources
Additional Journal Information:
Journal Volume: 321; Journal ID: ISSN 0378-7753
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1341186