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Layered Li4NiTeO6 was shown to reversibly release/uptake ∼2 lithium ions per formula unit with fair capacity retention upon long cycling. The Li electrochemical reactivity mechanism differs from that of Li2MO3 and is rooted in the Ni4+/ Ni2+ redox couple, that takes place at a higher potential than conventional LiNi1-xMnxO2 compounds. We explain this in terms of inductive effect due to Te6+ ions (or the TeO 6 6- moiety). © 2013 The Royal Society of Chemistry.

Li-ion batteries have contributed to the commercial success of portable electronics and may soon dominate the electric transportation market provided that major scientific advances including new materials and concepts are developed. Classical positive electrodes for Li-ion technology operate mainly through an insertion-deinsertion redox process involving cationic species. However, this mechanism is insufficient to account for the high capacities exhibited by the new generation of Li-rich (Li 1+x Ni y Co z Mn (1-x-y-z) O 2) layered oxides that present unusual Li reactivity. In an attempt to overcome both the inherent composition and the structural complexity of this class of oxides, we have designed structurally related Li 2 Ru 1-y Sn y O 3 materials that have a single redox cation and exhibit sustainable reversible capacities as high as 230 mA h g-1. Moreover, they present good cycling behaviour with no signs of voltage decay and a small irreversible capacity. We also unambiguously show, on the basis of an arsenal of characterization techniques, that the reactivity of these high-capacity materials towards Li entails cumulative cationic (M n+ →M (n+1)+) and anionic (O2-→O2 2-) reversible redox processes, owing to the d-sp hybridization associated with a reductive coupling mechanism. Because Li2 MO3 is a large family of compounds, this study opens the door to the exploration of a vast number of high-capacity materials. © 2013 Macmillan Publishers Limited. All rights reserved.

Understanding the origin of the high capacity displayed by Li 2MnO3-LiMO2 (M = Ni, Co) composites is essential for improving their cycling and rate capability performances. To address this issue, the Li2Ru1-yMnyO 3 series between the iso-structural layered end-members Li 2MnO3 and Li2RuO3 was investigated. A complete solid solution was found, with the 0.4 ≤ y ≤ 0.6 members showing sustainable reversible capacities exceeding 220 mAh·g -1 centered around 3.6 V vs Li+/Li. The voltage-composition profiles display a plateau on the first charge as compared to an S-type curve on subsequent discharge which is maintained on the following charges/discharges, with therefore a lowering of the average voltage. We show this profile to evolve upon long cycling due to a structural phase transition as deduced from XRD measurements. Finally we demonstrate, via XPS measurements, the oxidation and reduction of ruthenium (Ru5+/Ru4+) during cycling together with a partial activity of the Mn4+/Mn 3+ redox couple. Moreover, we provide direct evidence for the reversibility of the O2- → O- anionic process upon cycling, hence accounting for the high capacity displayed by these materials. This work, by capturing the main redox processes pertaining to these materials, should facilitate their development. © 2013 American Chemical Society.

Layered Li4NiTeO6 was shown to reversibly release/uptake ∼2 lithium ions per formula unit with fair capacity retention upon long cycling. The Li electrochemical reactivity mechanism differs from that of Li2MO3 and is rooted in the Ni4+/ Ni2+ redox couple, that takes place at a higher potential than conventional LiNi1-xMnxO2 compounds. We explain this in terms of inductive effect due to Te6+ ions (or the TeO 6 6- moiety). © 2013 The Royal Society of Chemistry.

Understanding the origin of the high capacity displayed by Li 2MnO3-LiMO2 (M = Ni, Co) composites is essential for improving their cycling and rate capability performances. To address this issue, the Li2Ru1-yMnyO 3 series between the iso-structural layered end-members Li 2MnO3 and Li2RuO3 was investigated. A complete solid solution was found, with the 0.4 ≤ y ≤ 0.6 members showing sustainable reversible capacities exceeding 220 mAh·g -1 centered around 3.6 V vs Li+/Li. The voltage-composition profiles display a plateau on the first charge as compared to an S-type curve on subsequent discharge which is maintained on the following charges/discharges, with therefore a lowering of the average voltage. We show this profile to evolve upon long cycling due to a structural phase transition as deduced from XRD measurements. Finally we demonstrate, via XPS measurements, the oxidation and reduction of ruthenium (Ru5+/Ru4+) during cycling together with a partial activity of the Mn4+/Mn 3+ redox couple. Moreover, we provide direct evidence for the reversibility of the O2- → O- anionic process upon cycling, hence accounting for the high capacity displayed by these materials. This work, by capturing the main redox processes pertaining to these materials, should facilitate their development. © 2013 American Chemical Society.

Li-ion batteries have contributed to the commercial success of portable electronics and may soon dominate the electric transportation market provided that major scientific advances including new materials and concepts are developed. Classical positive electrodes for Li-ion technology operate mainly through an insertion-deinsertion redox process involving cationic species. However, this mechanism is insufficient to account for the high capacities exhibited by the new generation of Li-rich (Li 1+x Ni y Co z Mn (1-x-y-z) O 2) layered oxides that present unusual Li reactivity. In an attempt to overcome both the inherent composition and the structural complexity of this class of oxides, we have designed structurally related Li 2 Ru 1-y Sn y O 3 materials that have a single redox cation and exhibit sustainable reversible capacities as high as 230 mA h g-1. Moreover, they present good cycling behaviour with no signs of voltage decay and a small irreversible capacity. We also unambiguously show, on the basis of an arsenal of characterization techniques, that the reactivity of these high-capacity materials towards Li entails cumulative cationic (M n+ →M (n+1)+) and anionic (O2-→O2 2-) reversible redox processes, owing to the d-sp hybridization associated with a reductive coupling mechanism. Because Li2 MO3 is a large family of compounds, this study opens the door to the exploration of a vast number of high-capacity materials. © 2013 Macmillan Publishers Limited. All rights reserved.

Li-ion batteries have contributed to the commercial success of portable electronics and may soon dominate the electric transportation market provided that major scientific advances including new materials and concepts are developed. Classical positive electrodes for Li-ion technology operate mainly through an insertion-deinsertion redox process involving cationic species. However, this mechanism is insufficient to account for the high capacities exhibited by the new generation of Li-rich (Li 1+x Ni y Co z Mn (1-x-y-z) O 2) layered oxides that present unusual Li reactivity. In an attempt to overcome both the inherent composition and the structural complexity of this class of oxides, we have designed structurally related Li 2 Ru 1-y Sn y O 3 materials that have a single redox cation and exhibit sustainable reversible capacities as high as 230 mA h g-1. Moreover, they present good cycling behaviour with no signs of voltage decay and a small irreversible capacity. We also unambiguously show, on the basis of an arsenal of characterization techniques, that the reactivity of these high-capacity materials towards Li entails cumulative cationic (M n+ →M (n+1)+) and anionic (O2-→O2 2-) reversible redox processes, owing to the d-sp hybridization associated with a reductive coupling mechanism. Because Li2 MO3 is a large family of compounds, this study opens the door to the exploration of a vast number of high-capacity materials. © 2013 Macmillan Publishers Limited. All rights reserved.

Understanding the origin of the high capacity displayed by Li 2MnO3-LiMO2 (M = Ni, Co) composites is essential for improving their cycling and rate capability performances. To address this issue, the Li2Ru1-yMnyO 3 series between the iso-structural layered end-members Li 2MnO3 and Li2RuO3 was investigated. A complete solid solution was found, with the 0.4 ≤ y ≤ 0.6 members showing sustainable reversible capacities exceeding 220 mAh·g -1 centered around 3.6 V vs Li+/Li. The voltage-composition profiles display a plateau on the first charge as compared to an S-type curve on subsequent discharge which is maintained on the following charges/discharges, with therefore a lowering of the average voltage. We show this profile to evolve upon long cycling due to a structural phase transition as deduced from XRD measurements. Finally we demonstrate, via XPS measurements, the oxidation and reduction of ruthenium (Ru5+/Ru4+) during cycling together with a partial activity of the Mn4+/Mn 3+ redox couple. Moreover, we provide direct evidence for the reversibility of the O2- → O- anionic process upon cycling, hence accounting for the high capacity displayed by these materials. This work, by capturing the main redox processes pertaining to these materials, should facilitate their development. © 2013 American Chemical Society.

Layered Li4NiTeO6 was shown to reversibly release/uptake ∼2 lithium ions per formula unit with fair capacity retention upon long cycling. The Li electrochemical reactivity mechanism differs from that of Li2MO3 and is rooted in the Ni4+/ Ni2+ redox couple, that takes place at a higher potential than conventional LiNi1-xMnxO2 compounds. We explain this in terms of inductive effect due to Te6+ ions (or the TeO 6 6- moiety). © 2013 The Royal Society of Chemistry.

Recently, the LiFeSO 4F material has been reported as the highest potential Fe-based cathode material for Li-ion batteries. Its working voltage vs. Li +/Li 0 jumps from 3.6 V to 3.9 V when LiFeSO 4F is synthesized with the fully ordered tavorite structure and the fully disordered triplite structure, respectively. The present study aims at rationalizing this voltage increase by means of DFT + U calculations combined with crystallographic and electrostatic analyses. We show that the triplite polymorph, although characterized by two distinct edge-shared crystallographic sites, locally exhibits corner-sharing connections between consecutive FeO 4F 2 octahedra, exactly as in the tavorite polymorph. As a consequence, edge-sharing connections exist in the lithiated triplite structure between consecutive FeO 4F 2 and LiO 4F 2 polyhedra. We then demonstrate that the origin of the voltage increase lies in the difference in the anionic networks of the two polymorphs, and more specifically in the electrostatic repulsions induced by the configuration of the fluorine atoms around the transition metal in the two polymorphs (trans- vs. cis-configurations in tavorite vs. triplite polymorphs). Such a finding should help in the design of novel high potential fluorosulphate materials, which beyond enhanced performances present sustainability attributes as they can be made from abundant elements and via low temperature eco-efficient processes. © 2012 The Royal Society of Chemistry.

The recent discovery of electrochemical activity at 3.6 V vs Li +/Li 0 in LiFeSO 4F has generated widespread research activity in this new family of fluorosulfate electrode materials aiming at either increasing the Fe 3+/Fe 2+ redox potential, searching for new active members, or extending this family to hydroxyl-fluorosulfates. Here we present a new low temperature single step synthesis of FeSO 4F 1-yOH y phases using FeF 3 and Fe 2(SO 4) 3•nH 2O as precursors. Using thorough chemical analytical techniques to test for F - content in conjunction with Mössbauer measurements, we demonstrate the existence of a limited solid solution (0.35 < y<1) within this system. Members pertaining to this solid solution have a redox activity ranging from 3.2 to 3.6 V vs Li +/Li 0 and show sustained reversible capacity retention of 130 mAh/g which makes them potentially interesting for Li-based polymer batteries. We demonstrate that the Li-insertion-deinsertion mechanism depends markedly on the sample F -content by using joint in situ XRD and Mössbauer spectroscopy. Moreover, we show the versatility of our synthetic approach by extending it to the elaboration of Fe 1-zM zSO 4F 1-yOH y phases with M = Ti and V. © 2012 American Chemical Society.

Recently, the LiFeSO 4F material has been reported as the highest potential Fe-based cathode material for Li-ion batteries. Its working voltage vs. Li +/Li 0 jumps from 3.6 V to 3.9 V when LiFeSO 4F is synthesized with the fully ordered tavorite structure and the fully disordered triplite structure, respectively. The present study aims at rationalizing this voltage increase by means of DFT + U calculations combined with crystallographic and electrostatic analyses. We show that the triplite polymorph, although characterized by two distinct edge-shared crystallographic sites, locally exhibits corner-sharing connections between consecutive FeO 4F 2 octahedra, exactly as in the tavorite polymorph. As a consequence, edge-sharing connections exist in the lithiated triplite structure between consecutive FeO 4F 2 and LiO 4F 2 polyhedra. We then demonstrate that the origin of the voltage increase lies in the difference in the anionic networks of the two polymorphs, and more specifically in the electrostatic repulsions induced by the configuration of the fluorine atoms around the transition metal in the two polymorphs (trans- vs. cis-configurations in tavorite vs. triplite polymorphs). Such a finding should help in the design of novel high potential fluorosulphate materials, which beyond enhanced performances present sustainability attributes as they can be made from abundant elements and via low temperature eco-efficient processes. © 2012 The Royal Society of Chemistry.

The recent discovery of electrochemical activity at 3.6 V vs Li +/Li 0 in LiFeSO 4F has generated widespread research activity in this new family of fluorosulfate electrode materials aiming at either increasing the Fe 3+/Fe 2+ redox potential, searching for new active members, or extending this family to hydroxyl-fluorosulfates. Here we present a new low temperature single step synthesis of FeSO 4F 1-yOH y phases using FeF 3 and Fe 2(SO 4) 3•nH 2O as precursors. Using thorough chemical analytical techniques to test for F - content in conjunction with Mössbauer measurements, we demonstrate the existence of a limited solid solution (0.35 < y<1) within this system. Members pertaining to this solid solution have a redox activity ranging from 3.2 to 3.6 V vs Li +/Li 0 and show sustained reversible capacity retention of 130 mAh/g which makes them potentially interesting for Li-based polymer batteries. We demonstrate that the Li-insertion-deinsertion mechanism depends markedly on the sample F -content by using joint in situ XRD and Mössbauer spectroscopy. Moreover, we show the versatility of our synthetic approach by extending it to the elaboration of Fe 1-zM zSO 4F 1-yOH y phases with M = Ti and V. © 2012 American Chemical Society.

Recently, the LiFeSO 4F material has been reported as the highest potential Fe-based cathode material for Li-ion batteries. Its working voltage vs. Li +/Li 0 jumps from 3.6 V to 3.9 V when LiFeSO 4F is synthesized with the fully ordered tavorite structure and the fully disordered triplite structure, respectively. The present study aims at rationalizing this voltage increase by means of DFT + U calculations combined with crystallographic and electrostatic analyses. We show that the triplite polymorph, although characterized by two distinct edge-shared crystallographic sites, locally exhibits corner-sharing connections between consecutive FeO 4F 2 octahedra, exactly as in the tavorite polymorph. As a consequence, edge-sharing connections exist in the lithiated triplite structure between consecutive FeO 4F 2 and LiO 4F 2 polyhedra. We then demonstrate that the origin of the voltage increase lies in the difference in the anionic networks of the two polymorphs, and more specifically in the electrostatic repulsions induced by the configuration of the fluorine atoms around the transition metal in the two polymorphs (trans- vs. cis-configurations in tavorite vs. triplite polymorphs). Such a finding should help in the design of novel high potential fluorosulphate materials, which beyond enhanced performances present sustainability attributes as they can be made from abundant elements and via low temperature eco-efficient processes. © 2012 The Royal Society of Chemistry.

The recent discovery of electrochemical activity at 3.6 V vs Li +/Li 0 in LiFeSO 4F has generated widespread research activity in this new family of fluorosulfate electrode materials aiming at either increasing the Fe 3+/Fe 2+ redox potential, searching for new active members, or extending this family to hydroxyl-fluorosulfates. Here we present a new low temperature single step synthesis of FeSO 4F 1-yOH y phases using FeF 3 and Fe 2(SO 4) 3•nH 2O as precursors. Using thorough chemical analytical techniques to test for F - content in conjunction with Mössbauer measurements, we demonstrate the existence of a limited solid solution (0.35 < y<1) within this system. Members pertaining to this solid solution have a redox activity ranging from 3.2 to 3.6 V vs Li +/Li 0 and show sustained reversible capacity retention of 130 mAh/g which makes them potentially interesting for Li-based polymer batteries. We demonstrate that the Li-insertion-deinsertion mechanism depends markedly on the sample F -content by using joint in situ XRD and Mössbauer spectroscopy. Moreover, we show the versatility of our synthetic approach by extending it to the elaboration of Fe 1-zM zSO 4F 1-yOH y phases with M = Ti and V. © 2012 American Chemical Society.

Li-ion batteries have empowered consumer electronics and are now seen as the best choice to propel forward the development of eco-friendly (hybrid) electric vehicles. To enhance the energy density, an intensive search has been made for new polyanionic compounds that have a higher potential for the Fe 2+/Fe 3+ redox couple. Herein we push this potential to 3.90 V in a new polyanionic material that crystallizes in the triplite structure by substituting as little as 5 atomic per cent of Mn for Fe in Li(Fe 1-δ Mn δ)SO 4 F. Not only is this the highest voltage reported so far for the Fe 2+/Fe 3+ redox couple, exceeding that of LiFePO 4 by 450 mV, but this new triplite phase is capable of reversibly releasing and reinserting 0.7-0.8 Li ions with a volume change of 0.6% (compared with 7 and 10% for LiFePO 4 and LiFeSO 4F respectively), to give a capacity of ∼125 mA h g -1. © 2011 Macmillan Publishers Limited. All rights reserved.

We demonstrate here the reversible electrochemical insertion of lithium into the hybrid porous solid FeIII(OH)0.8F0.2[O2C-C6H4-CO2]. Used as an electrode in Li-half cell, this material shows a reversible redox process around 3.0V vs. Li+/Li° exchanging 0.6Li per formula unit with interesting capacity retention and rate capability. Moreover, it reveals an interesting feature for MOFs with large tunnels: the uptake of electrolyte molecules within their channels, which facilitates ionic transport in MOFs. Mixed valence in MOFs opens new opportunities for the elaboration of materials with tuneable properties for various applications. © 2007 Elsevier B.V. All rights reserved.

There's more to LiFe: When used as an electrode in a lithium half cell, the metal-organic framework [LixFeIIxFe III1-x(OH)0.8-F0.2L] (L = O 2CC6H4CO2) shows a reversible redox process around 3.0 V versus Li+/ Li0 with interesting capacity retention and rate capability (see voltage profile for a [Li xFe(OH)0.8F0.2L] half cell; inset: representation of lithium insertion upon oxidation to Li+). (Graph Presented). © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.

There's more to LiFe: When used as an electrode in a lithium half cell, the metal-organic framework [LixFeIIxFe III1-x(OH)0.8-F0.2L] (L = O 2CC6H4CO2) shows a reversible redox process around 3.0 V versus Li+/ Li0 with interesting capacity retention and rate capability (see voltage profile for a [Li xFe(OH)0.8F0.2L] half cell; inset: representation of lithium insertion upon oxidation to Li+). (Graph Presented). © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.

We demonstrate here the reversible electrochemical insertion of lithium into the hybrid porous solid FeIII(OH)0.8F0.2[O2C-C6H4-CO2]. Used as an electrode in Li-half cell, this material shows a reversible redox process around 3.0V vs. Li+/Li° exchanging 0.6Li per formula unit with interesting capacity retention and rate capability. Moreover, it reveals an interesting feature for MOFs with large tunnels: the uptake of electrolyte molecules within their channels, which facilitates ionic transport in MOFs. Mixed valence in MOFs opens new opportunities for the elaboration of materials with tuneable properties for various applications. © 2007 Elsevier B.V. All rights reserved.

There's more to LiFe: When used as an electrode in a lithium half cell, the metal-organic framework [LixFeIIxFe III1-x(OH)0.8-F0.2L] (L = O 2CC6H4CO2) shows a reversible redox process around 3.0 V versus Li+/ Li0 with interesting capacity retention and rate capability (see voltage profile for a [Li xFe(OH)0.8F0.2L] half cell; inset: representation of lithium insertion upon oxidation to Li+). (Graph Presented). © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.

FePy (y = 1, 2, 4) anodes all react with lithium through a conversion reaction FePy + 3yLi → yLi3P + Fe 0 in their first discharge, leading to nanocomposite discharged electrodes described by nanosized Fe0 particles embedded in yLi 3P matrixes. From electrochemical and complementary in situ X-ray diffraction and high-resolution transmission electron microscopy studies, we deduce that the conversion reaction occurring during the first discharge is followed by two successive insertion and conversion processes in further cycles for the FeP electrode. The insertion process is highly reversible, leading to a capacity retention of 300 mA h g-1 and 1900 mA h cm-3 after 100 cycles, and corresponds to the formation of an intermediate tetragonal LiFeP phase as deduced from first-principles T = 0 K phase diagram calculations and preliminary Mössbauer analyses. We expect the kinetics of this reaction to be strongly limited by the increase in y, thus leading to an increasing capacity fading when increasing the y P/Fe ratio. © 2006 American Chemical Society.

FePy (y = 1, 2, 4) anodes all react with lithium through a conversion reaction FePy + 3yLi → yLi3P + Fe 0 in their first discharge, leading to nanocomposite discharged electrodes described by nanosized Fe0 particles embedded in yLi 3P matrixes. From electrochemical and complementary in situ X-ray diffraction and high-resolution transmission electron microscopy studies, we deduce that the conversion reaction occurring during the first discharge is followed by two successive insertion and conversion processes in further cycles for the FeP electrode. The insertion process is highly reversible, leading to a capacity retention of 300 mA h g-1 and 1900 mA h cm-3 after 100 cycles, and corresponds to the formation of an intermediate tetragonal LiFeP phase as deduced from first-principles T = 0 K phase diagram calculations and preliminary Mössbauer analyses. We expect the kinetics of this reaction to be strongly limited by the increase in y, thus leading to an increasing capacity fading when increasing the y P/Fe ratio. © 2006 American Chemical Society.

FePy (y = 1, 2, 4) anodes all react with lithium through a conversion reaction FePy + 3yLi → yLi3P + Fe 0 in their first discharge, leading to nanocomposite discharged electrodes described by nanosized Fe0 particles embedded in yLi 3P matrixes. From electrochemical and complementary in situ X-ray diffraction and high-resolution transmission electron microscopy studies, we deduce that the conversion reaction occurring during the first discharge is followed by two successive insertion and conversion processes in further cycles for the FeP electrode. The insertion process is highly reversible, leading to a capacity retention of 300 mA h g-1 and 1900 mA h cm-3 after 100 cycles, and corresponds to the formation of an intermediate tetragonal LiFeP phase as deduced from first-principles T = 0 K phase diagram calculations and preliminary Mössbauer analyses. We expect the kinetics of this reaction to be strongly limited by the increase in y, thus leading to an increasing capacity fading when increasing the y P/Fe ratio. © 2006 American Chemical Society.

We report the electrochemical study of cubic and monoclinic NiP2 polymorphs toward Li, as a candidate for anodic applications for Li-ion batteries. We found that the monoclinic form is the most attractive one performance-wise. Monoclinic NiP2 can reversibly uptake 5 lithium per formula unit, leading to reversible capacities of 1000 mAh/g at an average potential of 0.9 V vs Li+/Li°. From complementary X-ray diffraction (XRD) and HRTEM (high-resolution transmission electron microscopy) measurements, it was shown that, during the first discharge, the cubic phase undergoes a pure conversion process (NiP2 + 6 Li+ + 6e- → Ni° + 2Li3P) as opposed to a sequential insertion-conversion process for monoclinic NiP2. Such a different behavior rooted in subtle structural changes was explained through electronic structure calculations. Once the first discharged is achieved, both phases were shown to react with Li through a classical conversion process. More importantly, we report a novel way to design NiP2 electrodes with enhanced capacity retention and rate capabilities. It consists in growing the monoclinic NiP2 phase, through a vapor-phase transport process, on a commercial Ni-foam commonly used in Ni-based alkaline batteries. These new self-supported electrodes, based on chemically made interfaces, offer new opportunities to fully exploit the capacity gains provided by conversion reactions. © 2005 American Chemical Society.

The Li 5.5Mn 2.5P 4 and Li 7MnP 4 phases having a tetragonal structure (P 4/nmm, a = b = 4.176(1) Å and c = 5.978(1) Å) and a cubic structure (Fm3̄m a = 5.968(3) Å) were synthesized by a two-step process consisting in ball milling Li, Mn, and P powders followed by annealing at 800°C under argon in a sealed stainless steel tube. The resulting materials were tested on Li cells between 0.01 and 2 V. Both of them can reversibly react with Li, leading to reversible capacities as high as 1000 mAh/g, but only the Li 5.5Mn 2.5P 4 electrode can nicely maintain its initial capacity upon cycling. The origin of such a difference was found in the partial decomposition of Li 7MnP 4 in Li 3P and Mn nanoparticles at low potential, as deduced by in situ X-ray diffraction measurements. In contrast, no decomposition was shown to occur for the Li 5.5Mn 2.5P 4 electrode that shows the best capacity retention among of ternary Li xM yP 4 (M = Ti, V) so far studied. © 2005 American Chemical Society.

We report the electrochemical study of cubic and monoclinic NiP2 polymorphs toward Li, as a candidate for anodic applications for Li-ion batteries. We found that the monoclinic form is the most attractive one performance-wise. Monoclinic NiP2 can reversibly uptake 5 lithium per formula unit, leading to reversible capacities of 1000 mAh/g at an average potential of 0.9 V vs Li+/Li°. From complementary X-ray diffraction (XRD) and HRTEM (high-resolution transmission electron microscopy) measurements, it was shown that, during the first discharge, the cubic phase undergoes a pure conversion process (NiP2 + 6 Li+ + 6e- → Ni° + 2Li3P) as opposed to a sequential insertion-conversion process for monoclinic NiP2. Such a different behavior rooted in subtle structural changes was explained through electronic structure calculations. Once the first discharged is achieved, both phases were shown to react with Li through a classical conversion process. More importantly, we report a novel way to design NiP2 electrodes with enhanced capacity retention and rate capabilities. It consists in growing the monoclinic NiP2 phase, through a vapor-phase transport process, on a commercial Ni-foam commonly used in Ni-based alkaline batteries. These new self-supported electrodes, based on chemically made interfaces, offer new opportunities to fully exploit the capacity gains provided by conversion reactions. © 2005 American Chemical Society.

The Li 5.5Mn 2.5P 4 and Li 7MnP 4 phases having a tetragonal structure (P 4/nmm, a = b = 4.176(1) Å and c = 5.978(1) Å) and a cubic structure (Fm3̄m a = 5.968(3) Å) were synthesized by a two-step process consisting in ball milling Li, Mn, and P powders followed by annealing at 800°C under argon in a sealed stainless steel tube. The resulting materials were tested on Li cells between 0.01 and 2 V. Both of them can reversibly react with Li, leading to reversible capacities as high as 1000 mAh/g, but only the Li 5.5Mn 2.5P 4 electrode can nicely maintain its initial capacity upon cycling. The origin of such a difference was found in the partial decomposition of Li 7MnP 4 in Li 3P and Mn nanoparticles at low potential, as deduced by in situ X-ray diffraction measurements. In contrast, no decomposition was shown to occur for the Li 5.5Mn 2.5P 4 electrode that shows the best capacity retention among of ternary Li xM yP 4 (M = Ti, V) so far studied. © 2005 American Chemical Society.

The Li 5.5Mn 2.5P 4 and Li 7MnP 4 phases having a tetragonal structure (P 4/nmm, a = b = 4.176(1) Å and c = 5.978(1) Å) and a cubic structure (Fm3̄m a = 5.968(3) Å) were synthesized by a two-step process consisting in ball milling Li, Mn, and P powders followed by annealing at 800°C under argon in a sealed stainless steel tube. The resulting materials were tested on Li cells between 0.01 and 2 V. Both of them can reversibly react with Li, leading to reversible capacities as high as 1000 mAh/g, but only the Li 5.5Mn 2.5P 4 electrode can nicely maintain its initial capacity upon cycling. The origin of such a difference was found in the partial decomposition of Li 7MnP 4 in Li 3P and Mn nanoparticles at low potential, as deduced by in situ X-ray diffraction measurements. In contrast, no decomposition was shown to occur for the Li 5.5Mn 2.5P 4 electrode that shows the best capacity retention among of ternary Li xM yP 4 (M = Ti, V) so far studied. © 2005 American Chemical Society.

We report the electrochemical study of cubic and monoclinic NiP2 polymorphs toward Li, as a candidate for anodic applications for Li-ion batteries. We found that the monoclinic form is the most attractive one performance-wise. Monoclinic NiP2 can reversibly uptake 5 lithium per formula unit, leading to reversible capacities of 1000 mAh/g at an average potential of 0.9 V vs Li+/Li°. From complementary X-ray diffraction (XRD) and HRTEM (high-resolution transmission electron microscopy) measurements, it was shown that, during the first discharge, the cubic phase undergoes a pure conversion process (NiP2 + 6 Li+ + 6e- → Ni° + 2Li3P) as opposed to a sequential insertion-conversion process for monoclinic NiP2. Such a different behavior rooted in subtle structural changes was explained through electronic structure calculations. Once the first discharged is achieved, both phases were shown to react with Li through a classical conversion process. More importantly, we report a novel way to design NiP2 electrodes with enhanced capacity retention and rate capabilities. It consists in growing the monoclinic NiP2 phase, through a vapor-phase transport process, on a commercial Ni-foam commonly used in Ni-based alkaline batteries. These new self-supported electrodes, based on chemically made interfaces, offer new opportunities to fully exploit the capacity gains provided by conversion reactions. © 2005 American Chemical Society.