Alluaudite Na₂Co₂Fe(PO₄)₃ as an electroactive material for sodium ion batteries

Essehli, R.,Belharouak, I.,Ben Yahia, H.,Maher, K.,Abouimrane, A.,Orayech, B.,Calder, S.,Zhou, X. L.,Zhou, Z.,Sun, Y-K. The Royal Society of Chemistry 2015 Dalton Transactions Vol.44 No.17

<P>The electroactive orthophosphate Na<SUB>2</SUB>Co<SUB>2</SUB>Fe(PO<SUB>4</SUB>)<SUB>3</SUB> was synthesized using a solid state reaction. Its crystal structure was solved using the combination of powder X-ray- and neutron-diffraction data. This material crystallizes according to the alluaudite structure (S.G. <I>C</I>2/<I>c</I>). The structure consists of edge sharing [MO<SUB>6</SUB>] octahedra (M = Fe, Co) resulting in chains parallel to [−101]. These chains are linked together <I>via</I> the [PO<SUB>4</SUB>] tetrahedra to form two distinct tunnels in which sodium cations are located. The electrochemical properties of Na<SUB>2</SUB>Co<SUB>2</SUB>Fe(PO<SUB>4</SUB>)<SUB>3</SUB> were evaluated by galvanostatic charge–discharge cycling. During the first discharge to 0.03 V, Na<SUB>2</SUB>Co<SUB>2</SUB>Fe(PO<SUB>4</SUB>)<SUB>3</SUB> delivers a specific capacity of 604 mA h g<SUP>−1</SUP>. This capacity is equivalent to the reaction of more than seven sodium ions per formula unit. Hence, this is a strong indication of a conversion-type reaction with the formation of metallic Fe and Co. The subsequent charge and discharge involved the reaction of fewer Na ions as expected for a conversion reaction. When discharged to 0.9 V, the material intercalated only one Na<SUP>+</SUP>-ion leading to the formation of a new phase Na<SUB>3</SUB>Co<SUB>2</SUB>Fe(PO<SUB>4</SUB>)<SUB>3</SUB>. This phase could then be cycled reversibly with an average voltage of 3.6 V <I>vs.</I> Na<SUP>+</SUP>/Na and a capacity of 110 mA h g<SUP>−1</SUP>. This result is in good agreement with the theoretical capacity expected from the extraction/insertion of two sodium atoms in Na<SUB>3</SUB>Co<SUB>2</SUB>Fe(PO<SUB>4</SUB>)<SUB>3</SUB>.</P> <P>Graphic Abstract</P><P>Na<SUB>2</SUB>Co<SUB>2</SUB>Fe(PO<SUB>4</SUB>)<SUB>3</SUB> crystallizes with the alluaudite-type structure (S.G. <I>C</I>2/<I>c</I>) and plays a dual anode/cathode behavior in sodium ion batteries. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5dt00971e'> </P>

Unveiling the sodium intercalation properties in Na_1.86□_0.14Fe₃(PO₄)₃

Essehli, R.,Ben Yahia, H.,Maher, K.,Sougrati, M.T.,Abouimrane, A.,Park, J.-B.,Sun, Y.-K.,Al-Maadeed, M.A.,Belharouak, I. Elsevier Sequoia 2016 Journal of Power Sources Vol. No.

<P><B>Abstract</B></P> <P>The new compound Na<SUB>1.86</SUB>□<SUB>0.14</SUB>Fe<SUB>3</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB> was successfully synthesized via hydrothermal synthesis and its crystal structure was determined using powder X-ray diffraction data. Na<SUB>1.86</SUB>Fe<SUB>3</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB> was also characterized by operando XRD and Mössbauer spectroscopy, cyclic voltammetry, and galvanostatic cycling. Na<SUB>1.86</SUB>Fe<SUB>3</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB> crystallizes with the alluaudite-type structure with the eight coordinated Na1 and Na2 sodium atoms located within the channels. The combination of the Rietveld- and Mössbauer-analyses confirms that the sodium vacancies in the Na1 site are linked to a partial oxidation of Fe<SUP>2+</SUP> during synthesis. The electrochemical tests indicated that Na<SUB>1.86</SUB>Fe<SUB>3</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB> is a 3 V sodium intercalating cathode. At the current densities of 5, 10, and 20 mA g<SUP>−1</SUP>, the material delivers the specific capacities of 109, 97, and 80 mA h g<SUP>−1</SUP>, respectively. After 100 charge and discharge cycles, Na<SUB>1.86</SUB>Fe<SUB>3</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB> exhibited good sodium removal and uptake behavior although no optimizations of particle size, morphology, and carbon coating were performed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Na<SUB>1.86</SUB>□<SUB>0.14</SUB>Fe<SUB>3</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB> was synthesized via hydrothermal synthesis method. </LI> <LI> Na<SUB>1.86</SUB>□<SUB>0.14</SUB>Fe<SUB>3</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB> crystallizes with the Alluaudite-type structure. </LI> <LI> Operando in situ XRD and Mössbauer spectroscopy studies were carried on. </LI> <LI> The crystal structure of Na<SUB>1.86</SUB>□<SUB>0.14</SUB>Fe<SUB>3</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB> is stable during cycling. </LI> <LI> Na<SUB>1.86</SUB>□<SUB>0.14</SUB>Fe<SUB>3</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB> is a promising 3 V cathode material for sodium ion batteries. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Na1.86□0.14Fe3(PO4)3 was synthesized via hydrothermal synthesis method. Na1.86Fe3(PO4)3 crystallizes with the alluaudite-type structure. Na1.86Fe3(PO4)3 is a 3 V sodium intercalating cathode. At the current densities of 5, 10, and 20 mA g<SUP>−1</SUP>, the material delivers the specific capacities of 109, 97, and 80 mA h g<SUP>−1</SUP>, respectively. After 100 charge and discharge cycles, Na1.86Fe3(PO4)3 exhibited good sodium removal and uptake behavior with a stable crystal structure.</P> <P>[DISPLAY OMISSION]</P>

Iron titanium phosphates as high-specific-capacity electrode materials for lithium ion batteries

Essehli, R.,El Bali, B.,Faik, A.,Naji, M.,Benmokhtar, S.,Zhong, Y.R.,Su, L.W.,Zhou, Z.,Kim, J.,Kang, K.,Dusek, M. Elsevier Sequoia 2014 Journal of Alloys and Compounds Vol.585 No.-

Two iron titanium phosphates, Fe<SUB>0.5</SUB>TiOPO<SUB>4</SUB> and Fe<SUB>0.5</SUB>Ti<SUB>2</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB>, were prepared, and their crystal structures and electrochemical performances were compared. The electrochemical measurements of Fe<SUB>0.5</SUB>TiOPO<SUB>4</SUB> as an anode of a lithium ion cell showed that upon the first discharge down to 0.5V, the cell delivered a capacity of 560mAh/g, corresponding to the insertion of 5 Li's per formula unit Fe<SUB>0.5</SUB>TiOPO<SUB>4</SUB>. Ex-situ XRD reveals a gradual evolution of the structure during cycling of the material, with lower crystallinity after the first discharge cycle. By correlating the electrochemical performances with the structural studies, new insights are achieved into the electrochemical behaviour of the Fe<SUB>0.5</SUB>TiOPO<SUB>4</SUB> anode material, suggesting a combination of intercalation and conversion reactions. The Nasicon-type Fe<SUB>0.5</SUB>Ti<SUB>2</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB> consists of a three-dimensional network made of corners and edges sharing [TiO<SUB>6</SUB>] and [FeO<SUB>6</SUB>] octahedra and [PO<SUB>4</SUB>] tetrahedra leading to the formation of trimmers [FeTi<SUB>2</SUB>O<SUB>12</SUB>]. The first discharge of lithium ion cells based on Fe<SUB>0.5</SUB>Ti<SUB>2</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB> materials showed electrochemical activity of Ti<SUP>4+</SUP>/Ti<SUP>3+</SUP> and Fe<SUP>2+</SUP>/Fe<SUP>0</SUP> couples in the 2.5-1V region. Below this voltage, the discharge profiles are typical of phosphate systems where Li<SUB>3</SUB>PO<SUB>4</SUB> is a product of the electrochemical reaction with lithium; moreover, the electrolyte solvent is reduced. An initial capacities as high as 1100mAhg<SUP>-1</SUP> can be obtained at deep discharge. However, there is an irreversible capacity loss in Fe<SUB>0.5</SUB>Ti<SUB>2</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB> due to the occurrence of insulating products as Li<SUB>3</SUB>PO<SUB>4</SUB> and a solid electrolyte interface.

Extreme fast charging characteristics of zirconia modified LiNi_0.5Mn_1.5O₄ cathode for lithium ion batteries

Nisar, Umair,Amin, Ruhul,Essehli, Rachid,Shakoor, R.A.,Kahraman, Ramazan,Kim, Do Kyung,Khaleel, Mohammad A.,Belharouak, Ilias Elsevier 2018 Journal of Power Sources Vol.396 No.-

<P><B>Abstract</B></P> <P>LiNi<SUB>0.5</SUB>Mn<SUB>1.5</SUB>O<SUB>4</SUB> is a promising high-voltage cathode for lithium-ion battery fast charging applications. Aware of its electrochemical stability issues, the material's surface is modified with small amounts of zirconia (ZrO<SUB>2</SUB>) ranging from 0.5 to 2 wt% using a scalable ball milling process. The advantage of the coating has been demonstrated in electrochemical measurements performed at room temperature and 55 °C, and in cells discharged under high-rate conditions up to 80C. Of significance, the material coated with 1.0 wt% ZrO<SUB>2</SUB> has been cycled at the 40C rate for over a thousand cycles and retains 86% of its initial capacity. The material with 2.0 wt% ZrO<SUB>2</SUB> modification preserves 76% of its initial capacity when cycled at the 40C rate and 55 °C. The coated materials have shown excellent cycling stability when subjected to 6C (10-min) fast charging and C/3 discharging for 300 cycles. Compared to the uncoated material, the interfacial resistance of the zirconia modified LiNi<SUB>0.5</SUB>Mn<SUB>1.5</SUB>O<SUB>4</SUB> has been found to be much lower and does not significantly increase with increasing the coating amount. However, the electrochemical performances are still partly limited by both interfacial resistance at the beginning of charge and electrolyte diffusivity, particularly under higher rate cycling conditions. Overall, the strategy of ZrO<SUB>2</SUB> surface modification applied to LiNi<SUB>0.5</SUB>Mn<SUB>1.5</SUB>O<SUB>4</SUB> unveils the potential that the material could play in extreme fast charged electric vehicles.</P> <P><B>Highlights</B></P> <P> <UL> <LI> ZrO<SUB>2</SUB>-LiNi<SUB>0.5</SUB>Mn<SUB>1.5</SUB>O<SUB>4</SUB> withstands 80C-rate and demonstrates over thousand cycles at 40C. </LI> <LI> Charge transfer resistance at LiNi<SUB>0.5</SUB>Mn<SUB>1.5</SUB>O<SUB>4</SUB>/electrolyte is stable with coating. </LI> <LI> Origin of high-rate capability is correlated with the high kinetics at the material's interfaces. </LI> <LI> Surface modification of LiNi<SUB>0.5</SUB>Mn<SUB>1.5</SUB>O<SUB>4</SUB> enables extreme fast charging. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Neutron diffraction studies of the Na-ion battery electrode materials NaCoCr₂(PO₄)₃, NaNiCr₂(PO₄)₃, and Na₂Ni₂Cr(PO₄)₃

Yahia, H.B.,Essehli, R.,Avdeev, M.,Park, J.B.,Sun, Y.K.,Al-Maadeed, M.A.,Belharouak, I. Academic Press 2016 Journal of solid state chemistry Vol.238 No.-

<P>The new compounds NaCoCr2(PO4)(3), NaNiCr2(PO4)(3), and Na2Ni2Cr(PO4)(3) were synthesized by sol-gel method and their crystal structures were determined by using neutron powder diffraction data. These compounds were characterized by galvanometric cycling and cyclic voltammetry. NaCoCr2(PO4)(3), NaNiCr2(PO4)(3), and Na2Ni2Cr(PO4)(3) crystallize with a stuffed alpha-CrPO4-type structure. The structure consists of a 3D-framework made of octahedra and tetrahedra that are sharing corners and/or edges generating channels along [100] and [010], in which the sodium atoms are located. Of significance, in the structures of NaNiCr2(PO4)(3), and Na2Ni2Cr(PO4)(3) a statistical disorder Ni2+/Cr3+ was observed on both the 8g and 4a atomic positions, whereas in NaCoCr2(PO4)(3) the statistical disorder Co2+/Cr3+ was only observed on the 8g atomic position. When tested as negative electrode materials, NaCoCr2(PO4)(3), NaNiCr2(PO4)(3), and Na2Ni2Cr(PO4)(3) delivered specific capacities of 352, 385, and 368 mA h g(-1), respectively, which attests to the electrochemical activity of sodium in these compounds. (C) 2016 Elsevier Inc. All rights reserved.</P>