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Valvo, Mario
Publications (10 of 37) Show all publications
Aktekin, B., Valvo, M., Smith, R. I., Sörby, M. H., Marzano, F. L., Zipprich, W., . . . Brant, W. (2019). Cation Ordering and Oxygen Release in LiNi0.5-xMn1.5+xO4-y (LNMO): In Situ Neutron Diffraction and Performance in Li Ion Full Cells. ACS APPLIED ENERGY MATERIALS, 2(5), 3323-3335
Open this publication in new window or tab >>Cation Ordering and Oxygen Release in LiNi0.5-xMn1.5+xO4-y (LNMO): In Situ Neutron Diffraction and Performance in Li Ion Full Cells
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2019 (English)In: ACS APPLIED ENERGY MATERIALS, ISSN 2574-0962, Vol. 2, no 5, p. 3323-3335Article in journal (Refereed) Published
Abstract [en]

Lithium ion cells utilizing LiNi0.5Mn1.5O4 (LNMO) as the positive electrode are prone to fast capacity fading, especially when operated in full cells and at elevated temperatures. The crystal structure of LNMO can adopt a P4(3)32 (cation-ordered) or Fd (3) over barm (disordered) arrangement, and the fading rate of cells is usually mitigated when samples possess the latter structure. However, synthesis conditions leading to disordering also lead to oxygen deficiencies and rock-salt impurities and as a result generate Mn3+. In this study, in situ neutron diffraction was performed on disordered and slightly Mn-rich LNMO samples to follow cation ordering-disordering transformations during heating and cooling. The study shows for the first time that there is not a direct connection between oxygen release and cation disordering, as cation disordering is observed to start prior to oxygen release when the samples are heated in a pure oxygen atmosphere. This result demonstrates that it is possible to tune disordering in LNMO without inducing oxygen deficiencies or forming the rock-salt impurity phase. In the second part of the study, electrochemical testing of samples with different degrees of ordering and oxygen content has been performed in LNMO vertical bar vertical bar LTO (Li4Ti5O12) full cells. The disordered sample exhibits better performance, as has been reported in other studies; however, we observe that all cells behave similarly during the initial period of cycling even when discharged at a 10 C rate, while differences arise only after a period of cycling. Additionally, the differences in fading rate were observed to be time-dependent rather than dependent on the number of cycles. This performance degradation is believed to be related to instabilities in LNMO at higher voltages, that is, in its lower lithiation states. Therefore, it is suggested that future studies should target the individual effects of ordering and oxygen content. It is also suggested that more emphasis during electrochemical testing should be placed on the stability of samples in their delithiated state.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2019
Keywords
high-voltage spinel, neutron diffraction, LNMO, cation ordering, oxygen deficiency
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-387975 (URN)10.1021/acsaem.8b02217 (DOI)000469885300040 ()
Funder
Swedish Energy Agency, 42758-1Swedish Energy Agency, 39043-1StandUp
Available from: 2019-06-27 Created: 2019-06-27 Last updated: 2019-07-29Bibliographically approved
Blidberg, A., Valvo, M., Alfredsson, M., Tengstedt, C., Gustafsson, T. & Björefors, F. (2019). Electronic changes in poly(3,4-ethylenedioxythiophene)-coated LiFeSO4F during electrochemical lithium extraction. Journal of Power Sources, 418, 84-89
Open this publication in new window or tab >>Electronic changes in poly(3,4-ethylenedioxythiophene)-coated LiFeSO4F during electrochemical lithium extraction
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2019 (English)In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 418, p. 84-89Article in journal (Refereed) Published
Abstract [en]

The redox activity of tavorite LiFeSO4F coated with poly (3,4-ethylenedioxythiophene), i.e. PEDOT, is investigated by means of several spectroscopic techniques. The electronic changes and iron-ligand redox features of this LiFeSO4F-PEDOT composite are probed upon delithiation through X-ray absorption spectroscopy. The PEDOT coating, which is necessary here to obtain enough electrical conductivity for the electrochemical reactions of LiFeSO4F to occur, is electrochemically stable within the voltage window employed for cell cycling. Although the electronic configuration of PEDOT shows also some changes in correspondence of its reduced and oxidized forms after electrochemical conditioning in Li half-cells, its p-type doping is fully retained between 2.7 and 4.1 V with respect to Li+/Li during the first few cycles. An increased iron-ligand interaction is observed in LixFeSO4F during electrochemical lithium extraction, which appears to be a general trend for polyanionic insertion compounds. This finding is crucial for a deeper understanding of a series of oxidation phenomena in Li-ion battery cathode materials and helps paving the way to the exploration of new energy storage materials with improved electrochemical performances.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2019
Keywords
Li-ion batteries, Lithium iron sulphate fluoride, Tavorite structure, X-ray absorption spectroscopy, Conductive polymers, Anionic redox processes
National Category
Materials Chemistry Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-381567 (URN)10.1016/j.jpowsour.2019.02.039 (DOI)000462420500010 ()
Funder
Swedish Foundation for Strategic Research Swedish Research Council Formas, 245-2014-668Swedish Energy Agency, 2017-013531StandUpÅForsk (Ångpanneföreningen's Foundation for Research and Development)
Available from: 2019-04-16 Created: 2019-04-16 Last updated: 2019-04-16Bibliographically approved
Renman, V., Ojwang, D. O., Gómez, C. P., Gustafsson, T., Edström, K., Svensson, G. & Valvo, M. (2019). Manganese Hexacyanomanganate as a Positive Electrode for Nonaqueous Li-, Na-, and K-Ion Batteries. The Journal of Physical Chemistry C, 123(36), 22040-22049
Open this publication in new window or tab >>Manganese Hexacyanomanganate as a Positive Electrode for Nonaqueous Li-, Na-, and K-Ion Batteries
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2019 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 36, p. 22040-22049Article in journal (Refereed) Published
Abstract [en]

K2Mn[Mn(CN)(6)] is synthesized, characterized, and evaluated as possible positive electrode material in nonaqueous Li-, Na-, and K-ion batteries. This compound belongs to the rich and versatile family of hexacyanometallates displaying distinctive structural properties, which makes it interesting for ion insertion purposes. It can be viewed as a perovskite-like compound in which CN-bridged Mn(CN)(6) octahedra form an open framework structure with sufficiently large diffusion channels able to accommodate a variety of insertion cations. By means of galvanostatic cycling and cyclic voltammetry tests in nonaqueous alkali metal half-cells, it is demonstrated that this material is able to reversibly host Li+, Na+, and K+ ions via electrochemical insertion/deinsertion within a wide voltage range. The general electrochemical features are similar for all of these three ion insertion chemistries. An in operando X-ray diffraction investigation indicates that the original monoclinic structure is transformed into a cubic one during charging (i.e., removal of cations from the host framework) and that such a process is reversible upon subsequent cell discharge and cation reuptake.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2019
National Category
Physical Chemistry Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-395691 (URN)10.1021/acs.jpcc.9b06338 (DOI)000486360900021 ()
Funder
Swedish Research Council, 2011-6512Swedish Energy Agency, 2017-013531StandUpÅForsk (Ångpanneföreningen's Foundation for Research and Development), 18-317
Available from: 2019-10-24 Created: 2019-10-24 Last updated: 2019-10-24Bibliographically approved
Carboni, M., Naylor, A. J., Valvo, M. & Younesi, R. (2019). Unlocking high capacities of graphite anodes for potassium-ion batteries. RSC Advances, 9(36), 21070-21074
Open this publication in new window or tab >>Unlocking high capacities of graphite anodes for potassium-ion batteries
2019 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 9, no 36, p. 21070-21074Article in journal (Refereed) Published
Abstract [en]

Graphite is considered a promising candidate as the anode for potassium-ion batteries (KIBs). Here, we demonstrate a significant improvement in performance through the ball-milling of graphite. Electrochemical techniques show reversible K-intercalation into graphitic layers, with 65% capacity retention after 100 cycles from initial capacities and extended cycling beyond 200 cycles. Such an affinity of the graphite towards storage of K-ions is explained by means of SEM and Raman analyses. Graphite ball-milling results in a gentle mechanical exfoliation of the graphene layers and simultaneous defect formation, leading to enhanced electrochemical performance.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2019
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-391016 (URN)10.1039/c9ra01931f (DOI)000474306500065 ()
Funder
Swedish Energy Agency, 2017-013531ÅForsk (Ångpanneföreningen's Foundation for Research and Development), 18-317
Available from: 2019-08-21 Created: 2019-08-21 Last updated: 2019-08-21Bibliographically approved
Aktekin, B., Brant, W., Valvo, M., Marzano, F., Zipprich, W., Brandell, D. & Edström, K. (2018). Cation Ordering and Oxygen Release in LiNi0.5-xMn1.5+xO4-y (LNMO)—In Situ Neutron Diffraction and Performance in Li-Ion Full Cells. In: : . Paper presented at 2018 MRS Fall Meeting, Boston, MA, USA, November 25-30, 2018. Boston, MA, USA
Open this publication in new window or tab >>Cation Ordering and Oxygen Release in LiNi0.5-xMn1.5+xO4-y (LNMO)—In Situ Neutron Diffraction and Performance in Li-Ion Full Cells
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2018 (English)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

LiNi0.5Mn1.5O4 (LNMO) is a promising spinel-type positive electrode for lithium ion batteries as it operates at high voltage and possesses high power capability. However, rapid performance degradation in full cells, especially at elevated temperatures, is a problem. There has been a considerable interest in its crystal structure as this is known to affect its electrochemical performance. LNMO can adopt a P4332 (cation ordered) or Fd-3m (cation disordered) arrangement depending on the synthesis conditions. Most of the studies in literature agree on better electrochemical performance for disordered LNMO [1], however, a clear understanding of the reason for this behaviour is still lacking. This partly arises from the fact that synthesis conditions leading to disordering also lead to oxygen deficiency, rock-salt impurities and therefore generate some Mn3+ [2]. Most commonly, X-ray diffraction is used to characterize these materials, however, accurate structural analysis is difficult due to the near identical scattering lengths of Mn and Ni. This is not the case for neutron diffraction. In this study, an in-situ neutron diffraction heating-cooling experiment was conducted on slightly Mn-rich LNMO under pure oxygen atmosphere in order to investigate relationship between disordering and oxygen deficiency. The study shows for the first time that there is no direct relationship between oxygen loss and cation disordering, as disordering starts prior to oxygen release. Our findings suggest that it is possible to obtain samples with varying degrees of ordering, yet with the same oxygen content and free from impurities. In the second part of the study, highly ordered, partially ordered and fully disordered samples have been tested in LNMO∥LTO (Li4Ti5O12) full cells at 55 °C. It is shown that differences in their performances arise only after repeated cycling, while all the samples behave similarly at the beginning of the test. The difference is believed to be related to instabilities of LNMO at higher voltages, that is, in its lower lithiation states.

[1] A. Manthiram, K. Chemelewski, E.-S. Lee, Energy Environ. Sci. 7 (2014) 1339.

[2] M. Kunduraci, G.G. Amatucci, J. Power Sources. 165 (2007) 359–367.

Place, publisher, year, edition, pages
Boston, MA, USA: , 2018
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-375838 (URN)
Conference
2018 MRS Fall Meeting, Boston, MA, USA, November 25-30, 2018
Funder
StandUp
Available from: 2019-02-01 Created: 2019-02-01 Last updated: 2019-09-25Bibliographically approved
Berastegui, P., Tai, C.-W. & Valvo, M. (2018). Electrochemical reactions of AgFeO2 as negative electrode in Li- and Na-ion batteries. Journal of Power Sources, 401, 386-396
Open this publication in new window or tab >>Electrochemical reactions of AgFeO2 as negative electrode in Li- and Na-ion batteries
2018 (English)In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 401, p. 386-396Article in journal (Refereed) Published
Abstract [en]

AgFeO2 nanoparticles synthesized via precipitation at room temperature are investigated in Li- and Na-ion cells through electrode coatings with an alginate binder. The electrochemical reactions of AgFeO2 with Li+ and Na+ions, as well as its role as alternative negative electrode in these cell systems are carefully evaluated. Initial Li uptake causes irreversible amorphization of the AgFeO2 structure with concomitant formation of Ag0 nanoparticles. Further Li incorporation results in conversion into Fe0 nanoparticles and Li2O, together with Li-alloying of these Ag0 clusters. Similar mechanisms are also found upon Na uptake, although such processes are hindered by overpotentials, the capacity and reversibility of the reactions with Na+ ions being not comparablewith those of their Li+ counterparts. The behaviour of AgFeO2 at low potentials vs. Li+/Li displays a synergic pseudo-capacitive charge storage overlapping Li-Ag alloying/de-alloying. This feature is exploited in full cells having deeply lithiated AgFeO2 and LiFePO4 as negative and positive electrodes, respectively. These environmentally friendly iron-based full cells exhibit attractive cycle performances with ≈80% capacity retention after 1000 cycles without any electrolyte additive, average round trip efficiency of ≈89% and operational voltage of 3.0 V combined with built-in pseudo-capacitive characteristics that enable high cycling rates up to≈25C.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Silver ferrite, Li- and Na-ion batteries, Negative electrodes, Conversion reactions, Electrochemical alloying, Metallic nanoparticles
National Category
Materials Chemistry Inorganic Chemistry
Research subject
Chemistry
Identifiers
urn:nbn:se:uu:diva-374936 (URN)10.1016/j.jpowsour.2018.09.002 (DOI)000449444500044 ()
Funder
Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning, 245-2014-668Knut and Alice Wallenberg FoundationStandUp
Available from: 2019-01-24 Created: 2019-01-24 Last updated: 2019-01-25Bibliographically approved
Carboni, M., Naylor, A. J., Valvo, M. & Younesi, R. (2018). Graphite for K-ion Batteries: Stability and Formation of SEI layer. In: : . Paper presented at 5th International Conference on Sodium Batteries. Saint-Malo, France. November 12-15, 2018..
Open this publication in new window or tab >>Graphite for K-ion Batteries: Stability and Formation of SEI layer
2018 (English)Conference paper, Poster (with or without abstract) (Other academic)
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-374700 (URN)
Conference
5th International Conference on Sodium Batteries. Saint-Malo, France. November 12-15, 2018.
Available from: 2019-01-23 Created: 2019-01-23 Last updated: 2019-01-24Bibliographically approved
Renman, V., Valvo, M., Tai, C.-W., Gómez, C. P., Edström, K. & Liivat, A. (2018). Manganese pyrosilicates as novel positive electrode materials for Na-ion batteries. SUSTAINABLE ENERGY & FUELS, 2(5), 941-945
Open this publication in new window or tab >>Manganese pyrosilicates as novel positive electrode materials for Na-ion batteries
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2018 (English)In: SUSTAINABLE ENERGY & FUELS, ISSN 2398-4902, Vol. 2, no 5, p. 941-945Article in journal (Refereed) Published
Abstract [en]

A carbon-coated pyrosilicate, Na2Mn2Si2O7/C, was synthesized and characterized for use as a new positive-electrode material for sodium ion batteries. The material consists of 20–80 nm primary particles embedded in a ≈10 nm-thick conductive carbon matrix. Reversible insertion of Na+ ions is clearly demonstrated with ≈25% of its theoretical capacity (165 mA h g−1) being accessible at room temperature at a low cycling rate. The material yields an average potential of 3.3 V vs. Na+/Na on charge and 2.2 V on discharge. DFT calculations predict an equilibrium potential for Na2Mn2Si2O7 in the range of 2.8–3.0 V vs. Na+/Na, with a possibility of a complete flip in the connectivity of neighboring Mn-polyhedra – from edge-sharing to disconnected and vice versa. This significant rearrangement in Mn coordination (≈2 Å) and large volume contraction (>10%) could explain our inability to fully desodiate the material, and illustrates well the need for a new electrode design strategy beyond the conventional “down-sizing/coating” procedure.

National Category
Inorganic Chemistry Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-356076 (URN)10.1039/c7se00587c (DOI)000431422700003 ()
Funder
Swedish Research Council, 2011-6512Swedish Research Council, 2010-4824Swedish Research Council Formas, 245-2014-668Knut and Alice Wallenberg FoundationStandUp
Available from: 2018-07-13 Created: 2018-07-13 Last updated: 2018-10-05Bibliographically approved
Valvo, M., Doubaji, S., Saadoune, I. & Edström, K. (2018). Pseudocapacitive charge storage properties of Na2/3Co2/3Mn2/9Ni1/9O2 in Na-ion batteries. Electrochimica Acta, 276, 142-152
Open this publication in new window or tab >>Pseudocapacitive charge storage properties of Na2/3Co2/3Mn2/9Ni1/9O2 in Na-ion batteries
2018 (English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 276, p. 142-152Article in journal (Refereed) Published
Abstract [en]

The behaviour of Na2/3Co2/3Mn2/9Ni1/9O2 in composite electrodes is studied via Na half-cells utilizing a dedicated cyclic voltammetry approach. The application of increasing sweep rates enabled a detailed analysis of the red-ox peaks of this material. All peak currents due to cathodic/anodic processes demonstrated clear capacitive properties. This finding widens the picture of classical Na+ insertion/ extraction in this complex oxide, as purely diffusive processes of Na+ through its layers do not fully explain the pseudocapacitance displayed by its red-ox peaks, which are typically linked to concomitant oxidation state changes for its transition metal atoms and/or phase transitions. No phase transition was observed during in operando X-Ray diffraction upon charge to 4.2 V vs. Na+/Na, proving good structural stability for P2-NaxCo2/3Mn2/9Ni1/9O2 upon Na+ removal. The origin of such pseudocapacitive properties is likely nested in strong electrostatic interactions among the metal oxide slabs and a tendency to release Na+ from its crystallites, e.g. to form surface by-products upon air exposure. Such a reactivity induces defects (e.g. vacancies) in its lattice and charge compensation mechanisms are required to maintain an overall charge neutrality, thus ultimately influencing the electrochemical properties. Possible limiting factors for the performances of this compound in composite coatings are also discussed.

Keywords
Na-ion batteries, Na2/3Co2/3Mn2/9Ni1/9O2, Layered oxides, Positive electrodes, Pseudocapacitance
National Category
Materials Chemistry Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-356610 (URN)10.1016/j.electacta.2018.04.150 (DOI)000433042500016 ()
Funder
Swedish Research Council Formas, 245-2014-668
Note

Correction in: Electrochimica Acta 305 (2019) 514-516

DOI: 10.1016/j.electacta.2019.03.075

Available from: 2018-08-03 Created: 2018-08-03 Last updated: 2019-04-23Bibliographically approved
Wei, W., Valvo, M., Edström, K. & Nyholm, L. (2018). Size-dependent Electrochemical Performance of Monolithic Anatase TiO2 Nanotube Anodes for Sodium-ion Batteries. ChemElectroChem, 5(4), 674-684
Open this publication in new window or tab >>Size-dependent Electrochemical Performance of Monolithic Anatase TiO2 Nanotube Anodes for Sodium-ion Batteries
2018 (English)In: ChemElectroChem, Vol. 5, no 4, p. 674-684Article in journal (Refereed) Published
Abstract [en]

Well-defined, monolithic TiO2 nanotube thin films havebeen used as model anode electrodes to study Na-ion storage in anatase TiO2. It is shown that anatase TiO2 nanotubes with wall thicknesses up to 50 nm can be transformed into amorphous sodium titanate (e.g. Na0.2TiO2) nanotubes via an electrochemical activation process at about 0.2 V vs. Na+/Na. Due to the Na+ insertion and extraction reactions at about 0.55 and 0.75 V vs. Na+/Na, respectively, the activated TiO2 nanotubes exhibit reversible capacities of 170 mAh g-1. For the first time, it is shown that the nanotube length and wall thickness play critical roles in determining the electrochemical performances of this type of electrodes in Na-ion cells. An excellent rate performance, yielding capacities of about 33mAh g-1 at 20C and 161 mAh g-1 at C/5 rates, as well as a capacity retention of more than 97% after more than 350 cycles, could be achieved with nanotubes with a wall thickness of up to 20 nm. Thecycling rate for the nanotubes with a tube length of 4.5 μm should,however, be limited to 1C to guarantee a cycle life of about 200 cycles.

Keywords
TiO2, nanotubes, sodium, batteries, electrodes, free-standing, wall thickness, length
National Category
Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-337289 (URN)10.1002/celc.201701267 (DOI)000425380200015 ()
Funder
Swedish Research Council Formas, 245- 2014-668StandUp
Available from: 2017-12-21 Created: 2017-12-21 Last updated: 2018-05-07Bibliographically approved
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