Electrochemical Reactions of Iron Borates with Lithium: Electrochemical and in Situ Mössbauer and X-ray Absorption Studies

Abstract

Upon electrochemical reduction in a lithium cell, crystalline FeBO3 and Fe3BO6 give amorphous compounds, which can be cycled reversibly at low potential (Rowsell, J. Power Sources 2001, 97−98, 254). We report here capacities as high as 300 Ah/kg at the 14th cycle. The mechanism of reaction was investigated by step-potential electrochemical spectroscopy and in situ Mössbauer and X-ray absorption spectroscopies on electrochemical cells encapsulated in thin sealed plastic bags. These techniques confirm the reduction mechanism consisting of the early destruction of the crystallized borates and a direct FeIII−Fe0 multiphase reduction on first discharge. On recharge and subsequent cyclings, a reversible redox reaction occurs between Fe0 and FeII/III in an amorphous or nanocrystalline matrix.

Synthesis of nanospherical Fe3BO6 anode material for lithium-ion battery by the rheological phase reaction method

“…This is because that Fe 3 BO 6 begins to decompose at around 950 1C and gives birth to Fe 2 O 3 and B 2 O 3 . This result is in agreement with that of IbarraPalos et al [12]. Meanwhile, a slow weight loss observed on TG curve is because of the volatilization of B 2 O 3.…”

“…The compound undergoes framework disintegration, yielding amorphous phase that can be cycled with high reversibility. In the report of Ibarra-Palos and co-workers [12], the Fe 3 BO 6 has capacity retention of about 225 mAh g -1 after 10 cycles. However, the electrochemical properties of Fe 3 BO 6 in previous work were all tested at rather low current densities (10 and 5 mA g -1 , respectively), which limits its potential applications.…”

“…The study has demonstrated that Fe 3 BO 6 possesses low potential of redox reaction vs. Li/Li + , which make it suitable for anode material for lithium-ion battery. It is very interesting that the initial norbergite structure of Fe 3 BO 6 does not allow topotactic intercalation of lithium, but a structure transformation occurs on first discharge [11,12]. The compound undergoes framework disintegration, yielding amorphous phase that can be cycled with high reversibility.…”

In situ Mössbauer studies of electrochemical processes

“…In the borates FeBO 3 and Fe 3 BO 6 , the structures do not allow intercalation and the Mössbauer results [12] confirmed that the first cycle destroyed the crystalline borates. However the materials were then able to continue to cycle reversibly between Fe 0 and Fe 2+/3+ states, with the latter phases being probably nanocrystalline or amorphous.…”

Synthesis and Single Crystal X-ray Structure of the Monoclinic Sodium Copper Borate (Na2Cu2B12O21)

“…Some transition metal borates exhibit catalytic activity 9 , magnetic behavior [10][11][12] and reversible Li-ion uptake [13][14][15] . In addition, a boron atom may adopt triangular oxygen coordination, where three oxygen atoms form B(sp2)-O bonds, or tetrahedral oxygen coordination, where four oxygen atoms form B(sp3)-O bonds.…”