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• Ulvestad, Asbjørn; Reksten, Anita; Andersen, Hanne Flåten; Carvalho, Patricia Almeida; Jensen, Ingvild Julie Thue & Nagell, Marius Uv [Show all 9 contributors for this article] (2020). Crystallinity of silicon nanoparticles: Direct influence on the electrochemical performance of lithium ion battery anodes. ChemElectroChem. ISSN 2196-0216. 7(21), p. 4349–4253. doi: 10.1002/celc.202001108. Full text in Research Archive Show summary

  The use of silicon (Si) in the form of nanoparticles is one of the most promising routes for boosting the capacity of modern Li‐ion batteries. Many parameters influence the performance of Si making the comparison of materials complicated. The present work demonstrates a direct comparison of Si nanoparticles with amorphous and crystalline structures prepared through the same chemistry with the same particle size and morphology. The amorphous Si nanoparticles with an average diameter of 100 nm were synthesized through silane pyrolysis, and their crystalline analogues were obtained through subsequent annealing not altering size or morphology of the nanoparticles. Such direct comparison allows evaluation of the specific impact of crystallinity on the material's performance. From electrochemical analysis of these materials, the electrodes prepared from amorphous nanoparticles were found to exhibit improved cycle life compared to electrodes prepared from crystalline nanoparticles when the delithiation capacity of the anode was limited to 1000 mAh/gSi.

• Andersen, Hanne Flåten; Foss, Carl Erik Lie; Voje, Jorunn; Tronstad, Ragnar; Mokkelbost, Tommy & Vullum, Per Erik [Show all 9 contributors for this article] (2019). Silicon-carbon composite anodes from industrial battery grade silicon. Scientific Reports. 9(14814). doi: 10.1038/s41598-019-51324-4. Full text in Research Archive Show summary

  In this work, silicon/carbon composites for anode electrodes of Li-ion batteries are prepared from Elkem’s Silgrain® line. Gentle ball milling is used to reduce particle size of Silgrain, and the resulting Si powder consists of micrometic Si with some impurities. Silicon/carbon composite with CMC/SBR as a dual binder can achieve more than 1200 cycles with a capacity of 1000 mAh g−1 of Si. This excellent electrochemical performance can be attributed to the use of a buffer as a solvent to control the pH of the electrode slurry, and hence the bonding properties of the binder to the silicon particles. In addition, the use of FEC as an electrolyte additive is greatly contributing to a stabilized cycling by creating a more robust SEI layer. This work clearly demonstrates the potential of industrial battery grade silicon from Elkem.

• Ulvestad, Asbjørn; Andersen, Hanne Flåten; Jensen, Ingvild Julie Thue; Mongstad, Trygve; Mæhlen, Jan Petter & Prytz, Øystein [Show all 7 contributors for this article] (2018). Substoichiometric Silicon Nitride – An Anode Material for Li-ion Batteries Promising High Stability and High Capacity. Scientific Reports. 8. doi: 10.1038/s41598-018-26769-8. Full text in Research Archive Show summary

  Silicon is often regarded as a likely candidate to replace graphite as the main active anode material in next-generation lithium ion batteries; however, a number of problems impacting its cycle stability have limited its commercial relevance. One approach to solving these issues involves the use of convertible silicon sub-oxides. In this work we have investigated amorphous silicon sub-nitride as an alternative convertible silicon compound by comparing the electrochemical performance of a-SiNx thin films with compositions ranging from pure Si to SiN0.89. We have found that increasing the nitrogen content gradually reduces the reversible capacity of the material, but also drastically increases its cycling stability, e.g. 40 nm a-SiN0.79 thin films exhibited a stable capacity of more than 1,500 mAh/g for 2,000 cycles. Consequently, by controlling the nitrogen content, this material has the exceptional ability to be tuned to satisfy a large range of different requirements for capacity and stability.

• Ulvestad, Asbjørn; Mæhlen, Jan Petter & Kirkengen, Martin (2018). Silicon nitride as anode material for Li-ion batteries: Understanding the SiNx conversion reaction. Journal of Power Sources. ISSN 0378-7753. 399, p. 414–421. doi: 10.1016/j.jpowsour.2018.07.109. Full text in Research Archive Show summary

  An extensive research effort is being made to develop the next generation of anode materials for lithium ion batteries. A large part of this effort has been related to silicon, primarily due to its considerable theoretical capacity; however, very limited cycling stability has prevented widespread commercial adoption. A potential solution for this is to use convertible sub-stoichiometric silicon nitride (a-SiNx), which goes through an irreversible conversion reaction during the initial lithiation cycle, producing active silicon domains in an inactive, lithium conducting matrix. Relative to pure silicon, the resulting composite material has gained cycle life at the cost of reduced specific capacity. The specifics of the conversion reaction, however, have not yet been determined; hence, the impact of varying nitrogen content remains uncertain. In this work we develop a model reaction which relates the reversible and irreversible capacities of an electrode to the composition of the conversion products. By fitting this model to experimental data from a large number of a-SiNx thin film electrodes with different thickness and composition, we determine with a high probability that the matrix composition is Li2SiN2. From this, the reversible and irreversible capacities of the material can be predicted for a nitride of a given composition.

• Ulvestad, Asbjørn; Andersen, Hanne Flåten; Mæhlen, Jan Petter; Prytz, Øystein & Kirkengen, Martin (2017). Long-term cyclability of substoichiometric silicon nitride thin film anodes for Li-ion batteries. Scientific Reports. 7(1). doi: 10.1038/s41598-017-13699-0. Full text in Research Archive Show summary

  Silicon has been the subject of an extensive research effort aimed at developing new anode materials for lithium ion batteries due to its large specific and volumetric capacity. However, commercial use is limited by a number of degradation problems, many of which are related to the large volume change the material undergoes during cycling in combination with limited lithium-diffusivity. Silicon rich silicon oxides (SiOx), which converts into active silicon and inactive lithium oxide during the initial lithiation, have attracted some attention as a possible solution to these issues. In this work we present an investigation of silicon rich amorphous silicon nitride (a-SiNx) as an alternative convertible anode material. Amorphous SiN0.89 thin films deposited by plasma enhanced chemical vapour deposition show reversible reactions with lithium when cycled between 0.05 and 1.0 V vs. Li+/Li. This material delivers a reversible capacity of approximately 1,200 mAh/g and exhibits excellent cycling stability, with 41 nm a-SiN0.89 thin film electrodes showing negligible capacity degradation over more than 2,400 cycles.

• Garcia-Gusano, Diego; Espegren, Kari Aamodt; Lind, Arne & Kirkengen, Martin (2016). The role of the discount rates in energy systems optimisation models. Renewable and Sustainable Energy Reviews. ISSN 1364-0321. 59, p. 56–72. doi: 10.1016/j.rser.2015.12.359. Full text in Research Archive
• Mongstad, Trygve; Andersen, Hanne Flåten; Mæhlen, Jan Petter; Filtvedt, Werner Olav; Klette, Hallgeir & Nordseth, Ørnulf [Show all 7 contributors for this article] (2016). No Significant Effect of Phosphorous Doping on the Electrochemical Performance of Silicon-Carbon Composite Anodes for Li-ion Batteries. ECS Transactions. ISSN 1938-5862. 73(1), p. 275–280. doi: 10.1149/07301.0275ecst. Full text in Research Archive
• Ulvestad, Asbjørn; Mæhlen, Jan Petter & Kirkengen, Martin (2015). Silicon nitride coated silicon thin films as anodes for Li-ion batteries. ECS Transactions. ISSN 1938-5862. 64(22), p. 107–111. doi: 10.1149/06422.0107ecst. Full text in Research Archive
• Andersen, Hanne Flåten; Filtvedt, Werner Olav; Mæhlen, Jan Petter; Mongstad, Trygve; Kirkengen, Martin & Holt, Arve (2014). Production of Silicon Particles for High-Capacity Anode Material Yielding Outstanding Production Capacity. ECS Transactions. ISSN 1938-5862. 62(1), p. 97–105. doi: 10.1149/06201.0097ecst. Full text in Research Archive
• Nærland, Tine Uberg; Angelskår, Hallvard; Kirkengen, Martin; Søndenå, Rune & Marstein, Erik Stensrud (2012). The role of excess minority carriers in light induced degradation examined by photoluminescence imaging. Journal of Applied Physics. ISSN 0021-8979. 112(3). doi: 10.1063/1.4735992. Full text in Research Archive
• Kirkengen, Martin & Bergli, Joakim (2009). Slow relaxation and equilibrium dynamics in a two-dimensional Coulomb glass: Demonstration of stretched exponential energy correlations. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 79(7). doi: 10.1103/PhysRevB.79.075205. Full text in Research Archive
• Glatz, A.; Vinokur, VM; Bergli, Joakim; Kirkengen, Martin & Galperin, Yuri (2008). The Coulomb gap and low energy statistics for Coulomb glasses. Journal of Statistical Mechanics: Theory and Experiment. doi: 10.1088/1742-5468/2008/06/P06006. Full text in Research Archive
• Kirkengen, Martin; Bergli, Joakim & Galperin, Yuri (2007). Direct generation of charge carriers in c-Si solar cells due to embedded nanoparticles. Journal of Applied Physics. ISSN 0021-8979. 102. doi: 10.1063/1.2809368. Full text in Research Archive
• Kirkengen, Martin; Bergli, Joakim & Galperin, Yuri (2006). Coherent charge transport through an interface between a superconductor and hopping insulator: Role of barrier properties. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 74. Full text in Research Archive
• Aarhus, Lars Thore; Holmqvist, Knut; Kirkengen, Martin & Kristoffersen, Thor (2002). Generalized Two-Tier relevance filtering of compute game update events. In Wolf, Lars (Eds.), Proceedings of the 1st Workshop on Network and System Support for Games, NETGAMES 2002. Association for Computing Machinery (ACM). ISSN 9781581134933. p. 10–13. Full text in Research Archive
• Kirkengen, Martin & Galperin, Yuri (2000). Nonlinear Acoustic and Microwave absorption in disordered semiconductors. Physics Review. 62(24), p. 16624–16624. Full text in Research Archive

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• Svensson, Ann Mari; Mæhlen, Jan Petter; Kirkengen, Martin; Torgeir, Welo, NTNU & Bjørkeng, Per Kristian (2020). Snart kan batteriet vare lenger enn el-bilen. [Journal]. Aftenposten. Full text in Research Archive
• Ulvestad, Asbjørn; Koposov, Alexey; Skare, Marte Orderud; Mæhlen, Jan Petter; Andersen, Hanne Flåten & Prytz, Øystein [Show all 7 contributors for this article] (2018). Amorphous Silicon Nitride - A Novel Anode Material for Li-ion Batteries. Full text in Research Archive
• Kirkengen, Martin (2017). Reint samvit med elbil? [Radio]. Ekko. Full text in Research Archive
• Svensson, Ann Mari; Mokkelbost, Tommy; Mæhlen, Jan Petter; Kirkengen, Martin; Vie, Preben Joakim Svela & Vullum-Bruer, Fride [Show all 11 contributors for this article] (2017). Stortare kan gjøre batterier mer miljøvennlig. [TV]. NRK. Full text in Research Archive
• Vullum-Bruer, Fride; Kirkengen, Martin; Svensson, Ann Mari; Mokkelbost, Tommy; Mæhlen, Jan Petter & Tronstad, Ragnar [Show all 8 contributors for this article] (2017). Bindemiddel av alger kan øke rekkevidden på elbiler. [Journal]. Teknisk Ukeblad. Full text in Research Archive
• Vie, Preben Joakim Svela; Mæhlen, Jan Petter; Andersen, Hanne Flåten; Kirkengen, Martin; Lian, Torleif & Forseth, Sissel (2017). In-situ Diagnostics of Ageing Mechanisms in Li-ion Batteries using Entropy Spectroscopy and Incremental Capacity Analysis. Full text in Research Archive
• Vie, Preben Joakim Svela; Mæhlen, Jan Petter; Andersen, Hanne Flåten; Kirkengen, Martin; Lian, Torleif & Gilljam, Martin [Show all 7 contributors for this article] (2017). Understanding Ageing Mechanisms in Li-ion Batteries using Entropy Spectroscopy and Incremental Capacity Analysis. Full text in Research Archive
• Vie, Preben Joakim Svela; Mæhlen, Jan Petter; Andersen, Hanne Flåten; Kirkengen, Martin; Forseth, Sissel & Lian, Torleif [Show all 10 contributors for this article] (2017). Life and Safety for Li-ion Batteries in Maritime Conditions: The SafeLiLife - project. Full text in Research Archive
• Ulvestad, Asbjørn; Andersen, Hanne Flåten; Mæhlen, Jan Petter; Prytz, Øystein & Kirkengen, Martin (2016). Amorphous SiNx Thin Film Anodes for Li-Ion Batteries. Full text in Research Archive
• Ulvestad, Asbjørn; Andersen, Hanne Flåten; Mæhlen, Jan Petter; Prytz, Øystein & Kirkengen, Martin (2016). Amorphous SiNx Thin Film Anodes for Li-Ion Batteries. Full text in Research Archive
• Vie, Preben Joakim Svela; Mæhlen, Jan Petter; Andersen, Hanne Flåten; Kirkengen, Martin; Lian, Torleif & Gilljam, Martin [Show all 7 contributors for this article] (2016). Ageing of Li-ion Batteries at Nordic Maritime Conditions – in-situ Diagnostics. Full text in Research Archive
• Vie, Preben Joakim Svela; Mæhlen, Jan Petter & Kirkengen, Martin (2015). Li-ion batteries for Maritime Conditions - life and safety considerations. Full text in Research Archive
• Ulvestad, Asbjørn; Mæhlen, Jan Petter; Andersen, Hanne Flåten; Gunnæs, Anette Eleonora; Prytz, Øystein & Kirkengen, Martin (2015). Characterization of PECVD-Grown a-SiC:H for use as Coating for Silicon Thin Film Anodes in Li-Ion Batteries. Full text in Research Archive
• Ulvestad, Asbjørn; Mæhlen, Jan Petter; Andersen, Hanne Flåten; Xu, Chao; Prytz, Øystein & Kirkengen, Martin (2015). a-SiN:H and a-SiC:H Coated Silicon Thin Films as Anodes for Li-Ion Batteries. Full text in Research Archive
• Ulvestad, Asbjørn; Andersen, Hanne Flåten; Vie, Preben Joakim Svela; Mæhlen, Jan Petter; Prytz, Øystein & Kirkengen, Martin (2015). SiN and SiC Coated Silicon Thin Films as Anodes for Li-Ion Batteries. Full text in Research Archive
• Kirkengen, Martin; Bergli, Joakim & Galperin, Yuri (2007). Surface Plasmons in Solar Cells. Full text in Research Archive
• Kirkengen, Martin (2007). Surface Plasmons in Solar Cells. Full text in Research Archive
• Kirkengen, Martin (2017). Norske markedsmuligheter i de globale, fornybare verdikjedene. Institutt for energiteknikk. ISSN 9788270178964. Full text in Research Archive
• Kirkengen, Martin (2013). Casu-Vasu. Theoretical estimate. Institutt for energiteknikk. Full text in Research Archive
• Kirkengen, Martin (2008). Collective Electron Properties of Hopping Insulators and Hybrid Systems. Universitetet i Oslo. Full text in Research Archive
• Aarhus, Lars Thore; Holmqvist, Knut; Kirkengen, Martin & Kristoffersen, Thor (2002). Generalized two-tier relevance filtering of computer game update events. Norsk Regnesentral. Full text in Research Archive
• Kirkengen, Martin; Lous, Joachim & Mazaher, Shahrzade (2001). Behavior Definition Toolset - Interim Implementation. Full text in Research Archive

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