For the past decade, silicon (Si) as a material for negative electrodes of Li-ion batteries has been considered among the most promising candidates for replacing commonly used graphite. However, Si-based electrodes suffer from severe degradation, which depends on the type of Si materials used. Generally, the degradation of Si is mainly viewed in terms of particle fracturing during lithiation accompanied by constant growth of the solid electrolyte interphase (SEI). At the same time, the reversed process, delithiation, has received little attention. The present work demonstrates the morphological changes of the Si components of electrodes occurring during electrochemical cycling through electron microscopy analyses. These changes are rationalized through the migration of Si, resulting in the formation of Si dendrites embedded in SEI. With the assistance of ReaxFF modeling, we demonstrate that the delithiation predominantly drives this process. The present study reveals that fracturing of Si particles is not the only cause for degradation, as the Si surfaces dramatically change after prolonged cycling, resulting in the formation of Si dendrites.

Efforts to further enhance the capabilities of silicon as a lithium-ion battery anode are continuing into the realm of chemical composition. Adding varying amounts of other elements can significantly alter the material properties or side reactions, which influence electrochemical performance. Additionally, tuning the chemical composition combined with surface modifications can better enable application of silicon anodes in other devices such as hybrid supercapacitors. Prior work, among others, has shown different performance enhancement regimes depending on how much phosphorus is added to silicon-containing anodes [1, 2]. In particular, the amount of phosphorus from ppm levels to majority atomic fraction can result in enhancement in the conductivity, diffusivity, or forming altogether a wholly new protective matrix [3]. However, while the rate capability has been enhanced only primarily for delithiation, silicon-phosphorus (SiPx) anodes still suffer from similar capacity degradation issues as pure silicon anodes. In the present work, we attempt to address the capacity degradation issue by using a thin, conformal carbon coating to modify the solid-electrolyte interface (SEI) reaction. Firstly, amorphous nanoparticles of SiPx with a few atomic percent of phosphorus are prepared using silane and phosphine co-pyrolysis. Using an oscillating furnace at 800 degrees Celsius under a low flow of acetylene in Ar carrier gas, we are able to produce consistent, uniform carbon films on nanoparticle agglomerates with select thicknesses between 2 and 10 nm, validated using low voltage scanning transmission electron microscopy (LV-STEM), as shown in Figure 1. By comparing Si- and SiPx-containing anodes in electrochemical half cells, we can reproduce the rate capability results while demonstrating the effect of carbon coating on cycle life and capacity retention. Furthermore, the carbon coating’s effect on volume expansion for Si- and SiPx-containing anodes is studied in situ using an electrochemical dilatometer in half cell configuration. [1] Y. Domi, H. Usui, M. Shimizu, Y. Kakimoto, H. Sakaguchi, ACS Applied Materials & Interfaces 2016, 8, 7125-7132. [2] S. Huang, L.-Z. Cheong, D. Wang, C. Shen, ACS Applied Materials & Interfaces 2017, 9, 23672-23678. [3] F. T. Huld, S. Y. Lai, W. M. Tucho, R. Batmaz, I. T. Jensen, S. Lu, O. E. Eleri, A. Y. Koposov, Z. Yu, F. Lou, ChemistrySelect 2022, 7, e202202857. Figure 1

Silicon (Si) has shown its promises as anode material for next-generation high-energy lithium-ion batteries (LIBs) due to its high theoretical capacity 1 . However, its practical application has been impeded by the severe cyclic instability caused by a large volume change during (de) lithiation. Recently, a new family of silicon-based anode materials called “in-situ convertible-type anode materials” has emerged to resolve the cyclic instability of silicon. 2,3 This family includes sub-stoichiometric oxides, nitrides, and carbides of silicon (SiA x , where A = N, C, O). The working principle of these materials follow two mechanisms: (1) irreversible conversion and (2) reversible alloying/dealloying. During initial lithiation, the conversion reaction occurs, forming Si-Li nanodomains inside a stable Li-conductive matrix denoted as Li y Si x A (A=N, C, O). In the subsequent cycles, the Si-Li nanodomains reversibly alloying/dealloying with Li, while the Li-conductive matrix ensures stable cycling and good rate capability. Such composition mitigates the challenges associated with Si’s large volume change ensuring long-term cyclic stability. In this study, we demonstrate our approach on the development of silicon-rich, sub-stochiometric, amorphous silicon nitride (SiN x ) nanoparticles, as an in-situ convertible-type anode material and its long-term cyclic performance for LIBs. In this approach, the SiN x nanoparticles are produced via the decomposition of silane gas in the presence of ammonia using an industrially scalable, free space reactor (FSR), which is developed and customized in our research institute (IFE) (Fig. 1a). Proper proportions of silane and ammonia gases are introduced into the reactor, leading to the nucleation and growth of SiN x nanoparticles. The synthesized SiNx nanoparticles exhibited Si-rich domain and amorphous structure with particle size between 100 nm - 200 nm (Fig. 1b), as confirmed by SEM, TEM and XRD characterizations. The presence of nitrogen in silicon dominated composition is revealed by energy dispersive electron spectroscopy (EDS) and Fourier-transform infrared spectroscopy (FTIR). The scalability and reproducibility of the FSR synthesis method makes it a promising approach for the industrial production of SiNx for advance anode materials for LIBs. The electrochemical performance of the synthesized SiNx anode is evaluated by galvanostatic cycling and electrochemical impedance spectroscopy. The electrochemical performance of the SiNx performed on the electrodes with the active mass loading of 0.987 mg/cm 2 and cycled at C/5 rate has preserved its capacity about 852 mAh/g after around 600 cycles. As seen from Fig. 1c, the improved cyclic stability of the SiN x compared with pure silicon indicates that the Li-conductive matrix plays crucial role in stabilizing the anode. The authors emphasize the need for further investigation and collaboration, particularly in advance characterization, to better understand the composition and mechanisms of the Li-conductive matrix in the SiN x anode. Such detailed understanding can significantly benefit the conversion-type anode materials for their widespread use in future LIB technologies. References Zuo, X., Zhu, J., Müller-Buschbaum, P. & Cheng, Y.-J. Silicon based lithium-ion battery anodes: A chronicle perspective review. Nano Energy 31 , 113–143 (2017). Ulvestad, A. et al. Stoichiometry-Controlled Reversible Lithiation Capacity in Nanostructured Silicon Nitrides Enabled by in Situ Conversion Reaction. ACS Nano 15 , 16777–16787 (2021). Kilian, S. O. et al. Active Buffer Matrix in Nanoparticle-Based Silicon-Rich Silicon Nitride Anodes Enables High Stability and Fast Charging of Lithium-Ion Batteries. Advanced Materials Interfaces 9 , 2201389 (2022). Figure 1

Electrodes containing 60 wt% micron-sized silicon were investigated with electrolytes containing carbonate solvents and either LiPF6 or lithium bis(fluorosulfonyl)imide (LiFSI) salt. The electrodes showed improved performance, with respect to capacity, cycling stability, rate performance, electrode resistance and cycle life with the LiFSI salt, attributed to differences in the solid electrolyte interphase (SEI). Through impedance spectroscopy, cross sectional analysis using transmission electron microscopy (TEM) and focused ion beam (FIB) in combination with scanning electron microscopy (SEM), and electrode surface characterization by X-ray photoelectron spectroscopy (XPS), differences in electrode morphological changes, SEI composition and local distribution of SEI components were investigated. The SEI formed with LiFSI has a thin, inner, primarily inorganic layer, and an outer layer dominated by organic components. This SEI appeared more homogeneous and stable, more flexible and with a lower resistivity than the SEI formed in LiPF6 electrolyte. The SEI formed in the LiPF6 electrolyte appears to be less passivating and less flexible, with a higher resistance, and with higher capacitance values, indicative of a higher interfacial surface area. Cycling in LiPF6 electrolyte also resulted in incomplete lithiation of silicon particles, attributed to the inhomogeneous SEI formed. In contrast to LiFSI, where LiF was present in small grains in-between the silicon particles, clusters of LiF were observed around the carbon black for the LiPF6 electrolyte.

In modern Li-based batteries, alloying anode materials have the potential to drastically improve the volumetric and specific energy storage capacity. For the past decade silicon has been viewed as a "Holy Grail" among these materials; however, severe stability issues limit its potential. Herein, we present amorphous substoichiometric silicon nitride (SiNx) as a convertible anode material, which allows overcoming the stability challenges associated with common alloying materials. Such material can be synthesized in a form of nanoparticles with seamlessly tunable chemical composition and particle size and, therefore, be used for the preparation of anodes for Li-based batteries directly through conventional slurry processing. Such SiNx materials were found to be capable of delivering high capacity that is controlled by the initial chemical composition of the nanoparticles. They exhibit an exceptional cycling stability, largely maintaining structural integrity of the nanoparticles and the complete electrodes, thus delivering stable electrochemical performance over the course of 1000 charge/discharge cycles. Such stability is achieved through the in situ conversion reaction, which was herein unambiguously confirmed by pair distribution function analysis of cycled SiNx nanoparticles revealing that active silicon domains and a stabilizing Li2SiN2 phase are formed in situ during the initial lithiation.

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/g(Si).

Transition metal oxides potentially present higher specific capacities than the current anodes based on carbon, providing an increasing energy density as compared to commercial Li-ion batteries. However, many parameters could influence the performance of the batteries, which depend on the processing of the electrode materials leading to different surface properties, sizes or crystalline phases. In this work a comparative study of tin and titanium oxide nanoparticles synthesized by different methods, undoped or Li doped, used as single components or in mixed ratio, or alternatively forming a composite with graphene oxide have been tested demonstrating an enhancement in capacity with Li doping and better cyclability for mixed phases and composite anodes.

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.

Low-fat diets and exercise are generally assumed to ameliorate obesity-related metabolic dysfunctions, but the importance of exercise vs. dietary changes is debated. Male C57BL/6J mice were fed a high-fat/high-sucrose (HF/HS) diet to induce obesity and then either maintained on the HF/HS or shifted to low-fat (LF) diets containing either salmon or entrecote. For each diet, half of the animals exercised voluntarily for 8 weeks. We determined body composition, glucose tolerance, insulin sensitivity and hepatic triacylglycerol levels. The microbiota composition in cecal and fecal samples was analyzed using 16S ribosomal RNA gene amplicon sequencing. Voluntary exercise improved insulin sensitivity but did not improve glucose tolerance. Voluntary exercise did not reduce adiposity in mice maintained on an HF/HS diet but enhanced LF-induced reduction in adiposity. Hepatic triacylglycerol levels were reduced by voluntary exercise in LF- but not HF/HS-fed mice. Voluntary exercise induced shifts in the cecal and fecal microbiota composition and functional potential in mice fed LF or HF/HS diets. Whereas voluntary exercise improved insulin sensitivity, a switch to an LF diet was the most important factor related to body weight and fat mass reduction.

Silicon is a promising anode material for Li-ion batteries1. Silicon’s ability to alloy with lithium results in a theoretical capacity ten times higher than that for graphite. However, since this high capacity involves several lithium ions per silicon atom, silicon will expand during lithiation and contract during delithiation. The volume changes causes the solid-electrolyte interphase (SEI) to crack, leading to continuous SEI formation. This eventually results in electronic insulation of the Si particles and large amounts of consumed lithium2. Hence, there is a need for an electrolyte composition that forms an SEI with increased ability to withstand the volume changes. By changing the electrolyte salt, the reactions at the interphase between electrode and electrolyte also changes. Inspired by the work of Philippe et al.3, we have evaluated lithium bis(fluorosulfonyl)imide (LiFSI) as an alternative electrolyte salt to the commercial lithium hexafluorophosphate (LiPF6). Promising results were achieved with LiFSI as electrolyte salt in half-cells with micron-sized silicon as active material against circular Li foil as counter electrode. The silicon based anodes used are made of 60 wt% Si (Silgrain®, e-Si 400, a commercially available battery grade silicon from Elkem), with an average particle size of 3 µm, 10 wt% graphite (Timcal, KS6L), 15 wt% carbon black (Timcal, C-Nergy C65, CB) and 15 wt% Na-CMC binder (Sigma Aldrich Mw ~90000). Slurries were cast onto dendritic copper foil and the electrodes were cycled in 2016 coin cells. The reference electrolyte composition is 1M LiFSI in EC:PC:DMC (1:1:3) + 5 wt% FEC and 1 wt% VC. In this work, the performance of the silicon anodes are evaluated in full-cells with NMC as cathode. Performance in the reference electrolyte is compared to when LiPF6 is the electrolyte salt. In addition, the effect of increasing the LiFSI concentration is evaluated. The results include electrochemical performance and post mortem characterization of the silicon electrodes. The post mortem characterization includes XPS and cross sectional analysis to investigate how the electrolyte compositions affects the SEI. Cross sectional analysis is performed using focused ion beam in combination with scanning electron microscopy. [1] J. Ling et al. Journal of the Electrochemical Society, 154 (3), A156-A161, 2007. [2] H. Wu et al. Nano Today, 7, (5), 414-429, 2012. [3] B. Philippe et al. Journal of the American Chemical Society, 135, 9829-9842, 2013.

The degradation and ageing of Li-ion batteries will in many cases contribute to reduced thermal stability which potentially affects the safety performance of the batteries. The fact that aging of lithium-ion cells leads to a reduced capacity and cell life, is extensively covered in the literature by several research groups, e.g. Vetter[1]. The safety effects of ageing are far less studied, with only a handful of empirical studies published, e.g. [2-4]. This poster presents ageing data and safety aspects of large commercial Li-ion cells. The cells have been aged and cycled at 5, 25 and 45 °C. Several diagnostic tools have been applied to characterise the ageing mechanisms. These tools include high power pulse characterisation, entropy spectroscopy, incremental capacity analysis and impedance spectroscopy. The ageing mechanisms are however different at low and high temperatures and this will affect the thermal stability of the aged cells. The thermal stability of cells which have been aged with different ageing mechanisms was characterized with an Accelerated Rate Calorimeter (ARC). It was e.g. observed that a cell cycled at 5 °C for 3000 cycles reaching 70% State-of-Health showed a reduced thermal runaway limit from 240 to 150 °C compared to the uncycled cell. This was also lower than the exotherm onset temperature for the uncycled cell. References Vetter, J., et al., Ageing mechanisms in lithium-ion batteries. Journal of Power Sources, 2005. 147(1-2): p. 269-281. Fleischhammer, M., et al., Interaction of cyclic ageing at high-rate and low temperatures and safety in lithium-ion batteries. Journal of Power Sources, 2015. 274: p. 432-439. Gilljam, M., et al., 7E. Effect of electrical energy and aging on cell safety, in Safety of Lithium Batteries, J. Garche and K. Brandt, Editors. 2017, Elsevier. Friesen, A., et al., Influence of temperature on the aging behavior of 18650-type lithium ion cells: A comprehensive approach combining electrochemical characterization and post-mortem analysis. Journal of Power Sources, 2017. 342: p. 88-97.

Despite a decade of extensive research, silicon, as material for anodes of lithium ion batteries, still has not become a practical solution. Suffering from enormous expansion/contraction during lithiation/delithiation cycles, silicon undergoes rapid self-destruction resulting in battery failure. To counteract the degradation several options has been explored over the years. Those include downsizing of the material to nanoparticles, doping and coating with organic or inorganic shells. An alternative approach was proposed to mitigate the structural destruction of silicon, which is preparation of the alloyed materials. In the present work we demonstrate the use of nanostructured amorphous substoichiometric silicon nitride as such alternative anode material. We demonstrate that upon lithiation, silicon nitride forms lithiated subunits of silicon and ternary phase of lithium silicon nitride, which serves as a matrix material. Such phase separation leads to remarkable stability: the nanostructured thin films of SiNx allowed fabrication of electrodes exhibiting capacities above 1500 mAh/g for 2000 cycles. To achieve sufficient capacities for the practical applications, we demonstrate the application of this principle to particle-based composite electrodes, using SiNx nanoparticles fabricated through a CVD process. Such amorphous substoichiometric nanoparticles demonstrated reversible capacities above 1000 mAh/g and excellent cycling stability over several hundred cycles. We also demonstrate the effects of chemical composition on initial and long-term cycling stability of nanostructured silicon nitride.

Silicon is a promising high capacity anode material for Li-ion batteries (LIBs)1. Compared to graphite, silicon has ten times higher theoretical capacity, due to the ability to form a Li-rich alloy. The challenge with silicon is the large volume expansion during lithiation causing the solid-electrolyte interphase (SEI) to crack, exposing fresh electrode surface, which again leads to the formation of more SEI. This continuous formation of SEI during operation consumes lithium and results in very thick SEI. Therefore, there is a need for an electrolyte composition that creates a strong and/or flexible SEI that can withstand silicon’s volume expansion during operation. One way to manipulate the reactions at the interface between electrode and electrolyte during operation is to change the lithium salt. Philippe et al.2 evaluated the performance of the salt lithium bis(fluorosulfonyl)imide (LiFSI) compared to LiPF6 for anodes of nano-sized silicon, and found that LiFSI resulted in better performance. The proposed reason for improved performance was that the fluorination of the silicon particles surface was avoided. Also, LiFSI has a lower susceptibility towards hydrolysis compared to LiPF6. Hence, it does not form HF in the presence of trace amounts of water. In this work, we present the performance of LiFSI as electrolyte salt for LIBs based on micron-sized silicon as anode material. More specifically, the silicon based anodes used in this work are made of 60 wt% Si (Silgrain®, e-Si 400, a commercially available battery grade silicon from Elkem), with an average particle size of 3 µm, 10 wt% graphite (Timcal, KS6L), 15 wt% carbon black (Timcal, C-Nergy C65, CB) and 15 wt% Na-CMC binder (Sigma Aldrich Mw ~90000). Slurries were cast onto dendritic copper foil. The electrodes were cycled in 2016 or 2032 coin cells. The reference electrolyte composition is 1M LiFSI in EC:PC:DMC (1:1:3) + 5 wt% FEC and 1 wt% VC. Furthermore, the effect of increasing concentrations of salt will be evaluated. The work also includes optimization of the amount of the additive FEC. Half cell tests were conducted with circular Li foil as counter electrode, while full cell tests were conducted with layered oxides, such as NMC or NCA, as cathode. When running full cell experiments the failure mechanism and SEI at the silicon anode is different from half cell experiments3. This due to less cycleable lithium in the cell. The difference of the SEI for half cell and full cell configuration is also investigated in this work. The results presented here include both electrochemical performance and post mortem characterization. The post mortem characterization include FTIR and cross sectional analysis of cycled silicon electrodes, in order to evaluate the SEI formed when LiFSI is the electrolyte salt. Cross sectional analysis is performed by focused ion beam in combination with scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results are compared to the performance of the same electrodes with LiPF6 as electrolyte salt. Ling and J. R. Dahn (2007) Journal of the Electrochemical Society, 154 (3), A156-A161. Philippe, R. Dedryvère, M. Gorgoi, H. Rensmo, D. Gonbeau and K. Edström (2013) Journal of the American Chemical Society, 135, 9829-9842. Dupré, P. Moreau, E. De Vito, L. Quazuguel, M. Boniface, A. Bordes, C. Rudisch, P. Bayle-Guillemaud and D. Guyomard (2016) Chemistry of Materials, 28, 2557-2572.

Silicon has a great potential as anode material for lithium ion batteries due to its high theoretical capacity; however, there are several obstacles that need to be overcome in order to make it a commercially viable option. Two of the main issues stem from the fact that silicon undergoes a large volume change during lithiation and delithiation (1). This makes forming a stable solid electrolyte interphase (SEI) difficult, resulting in a continuous loss of electrolyte and lithium as SEI is formed and broken each cycle. Uneven expansion and contraction also causes the silicon to fracture, both exposing new surface on which more SEI might form, as well as electrically disconnecting material from the electrode, rendering it inactive. One method to reduce these effects has been to use so-called in-situ convertible oxides, like tin oxide and silicon sub-oxide. In this work we investigate the use of amorphous silicon nitride as an alternative convertible alloy anode material. Silicon nitride is believed to form lithiated silicon and lithium nitride or one of several lithium silicon nitride ternary phases during initial lithiation (2, 3). The resulting material therefore believed to combine the high lithium storage capacity of silicon with the high lithium ion conductivity and structural stabilization of inactive lithium containing nitrides. This principle has been investigated in both a thin film electrode system, using PECVD deposited a-SiNx:H thin films, and particle based composite electrodes with amorphous SiNx nanoparticles made in an in-house developed synthesis reactor. By comparing materials with different nitrogen content, the effect of nitrogen content on the materials lithiation capacity, Coulombic efficiency, and cycling stability was explored. Figure 1 shows the cycling performance of an a-SiNx thin film electrode compared to a pure Si reference, demonstrating that, at the cost of reduced initial capacity, improved cycling stability is gained. The same principle is shown in Figure 2 for more commercially relevant particle based electrodes, demonstrating that electrodes with capacity in excess of 1000 mAh/g can be made without compromising the cycling stability. Stoichiometric silicon nitride, on the other hand, exhibited negligible capacity, underlining the importance of understanding the material characteristics in order to fully utilize its potential.

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.

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.

Nano-crystalline Mg2Si (Mg67Si33) and its Si-rich eutectic (Mg47Si53) composition were synthesized by hydrogen desorption-recombination process, casting and rapid solidification techniques. The synthesis of Mg2Si meets experimental challenges due to a significant difference in the melting temperatures of Mg (650 degrees C) and Si (1414 degrees C) and due to easy vaporization of magnesium metal. As cast alloys were obtained by induction melting the precursors, Mg and Si, followed by the casting and water quenching. These alloys were rapidly solidified using a chill block melt spinning which produces ribbons with fine dendritic morphology and a grain size close to 100 nm. Hydrogen desorption-recombination process of MgH2-Si mixture resulted in a release of similar to 4.67 wt % H and formation of Mg2Si. The microstructure of the alloys has been studied using Scanning Electron Microscopy and the relationship between microstructure and electrochemical properties as anodes of the lithium ion batteries was characterised. The electrochemical tests indicate that Si rich eutectic electrode shows a higher charge-discharge capacity than the Mg2Si intermetallic. Rapidly solidified Mg2Si and Mg2Si + Si alloys showed the highest initial discharge capacities of 989 mAh/g and 1283 mAh/g, respectively, superior to the alloys prepared by hydrogen desorption-recombination process and casting. The presence of electrolyte additives FEC (5%) and VC (1%) resulted in the formation of the stable SEI layer and enhanced the cycling capacity of the electrodes. Electrochemical Impedance Spectroscopy (EIS) was used to characterize the anode electrodes on cycling. A mathematical model for accounting the impedance response was utilised. The EIS response showed an increased overall resistance for the Mg2Si eutectic Si-containing alloy electrodes when compared to the electrodes based on a stoichiometric Mg2Si. Long-term cycling resulted in increased charge transfer resistance, which slowed down the electrochemical processes at the surface of the electrodes. (C) 2017 Elsevier B.V. All rights reserved.

In order to acquire reproducible electrodes relevant for Li ion batteries new MgH2 electrodes are successfully obtained from homogenous slurries in N-Methyl-2-Pyrrolidone “NMP” solvent. The electrodes are aimed to elucidate the contribution of the cell components to the electrochemical cycling, in terms of morphology and composition. Various electrode preparations were tested and compared regarding their interaction with Li in a half-cell. The obtained electrochemical cycling curves are discussed according to the ball-milling-induced structural morphology changes and presence of carbon additives, along with the effect of the kinetic rate on the conversion reaction mechanism.

SUMMARY Using an industry-relevant method of production we have demonstrated production of doped silicon nanoparticles for Li-ion batteries. The particles have been characterized and tested in Li-ion battery half-cells for demonstration of the performance as Li ion storage material in the anode. In this presentation we will show the results regarding the characterization of the particles as well as the performance results of the material in Li-ion half cells. BACKGROUND The use of silicon as part of the anode in Li-ion batteries enhances the potential storage capacity greatly. While the graphite anode used in standard Li-ion batteries has a theoretical capacity of 372 mAh/g, the theoretical capacity for Si is 3,572 mAh/g [1]. However, to be able to absorb the sufficient amount of Li ions reversibly, the silicon material needs to be nanostructured [2]. EXPERIMENTAL IFE has earlier demonstrated production of silicon particles prepared using a silane-based free-space reactor, which allows control of particle size distribution and crystallinity and a high production capacity [3]. In this work, the setup was modified to allow for introduction of phosphine gas in the production process. The intention was to introduce phosphorous dopant atoms to modify the electrical conductivity of the silicon material. The current particles were produced with a silane flow rate of 5 slm, and 5 slm of 3% phosphine diluted in He. Thus, the P concentration in the process gases was 3% with respect to Si. The production rate at 100% yield would be about 400 g/h, while the product recovered from the process typically was between 100 and 200 g/h. The processing temperature was varied from 475 °C to 600 °C to produce particles with different properties. All electrochemical tests were performed in a crimped 2032 coin cell with lithium metal used as a counter electrode, with a polymer separator (Celgard 3401) and 1 M LiPF6 in 1:1 EC/DMC electrolyte (LP30, BASF). For some experiments, 10 wt% fluoroethylene carbonate (FEC) was used as electrolyte additive. The cells were cycled at 25 °C between 0.05 and 1.0 V with a constant C-rate of C/10 (after initial 3 cycles at C/20) using an Arbin Battery cycler (Arbin Instruments). RESULTS AND CONCLUSIONS The phosphorus content of the particles was by inductively coupled plasma mass spectrometry (ICP-MS) and energy-dispersive x-ray spectroscopy (EDS) measured to be in the range of 1.7-1.8% with respect to silicon. Thus, it seems that the utilization of the phosphine is not complete, or phosphorous binds to materials which are not recovered from the production process. The particle size distribution was centered around 600 nm as measured by laser scattering in a Malvern Mastersizer 2000. SEM and TEM revealed that the particles consisted of aggregates of spherical silicon particles with a primary particle size of 50-400 nm. X-ray diffraction showed that we could produce amorphous or crystalline particles depending on the temperature of the process. Cycling of the particles in lithium battery half cells showed a life time of about 300 cycles for doped and undoped particles. Some measurements indicate a better conductivity of the doped material but the results were not conclusive. The cells were cycled with a limited capacity regime where the capacity was set to 1000 mAh/g(Si) and thus the end-voltage could vary. The most pronounced difference in the cycling performance between doped and undoped silicon particles was a shift in the increase in end voltage for the doped particles: While end-voltage increased from 0.4 V to 0.6 V over the first 25 cycles, this development is stretched out over the first 50 cycles or more for doped particles. See the attached figure for further details. References [1] D. Larcher, S. Beattie, M. Morcrette, K. Edström, J.-C. Jumas, and J.-M. Tarascon, “Recent findings and prospects in the field of pure metals as negative electrodes for Li-ion batteries,” J. Mater. Chem., vol. 17, no. 36, p. 3759, 2007. [2] H. Kim, M. Seo, M. H. Park, and J. Cho, “A critical size of silicon nano-anodes for lithium rechargeable batteries,” Angew. Chemie - Int. Ed., vol. 49, no. 12, pp. 2146–2149, 2010. [3] H. F. Andersen, W. O. Filtvedt, J. P. Mæhlen, T. Mongstad, M. Kirkengen, and A. Holt, “Production of Silicon Particles for High-Capacity Anode Material, Yielding Outstanding Production Capacity,” ECS Trans., vol. 62, no. 1, pp. 97–105, 2014. Figure 1

In this paper we demonstrate production of doped silicon nanoparticles and testing of the material in Li-ion battery half cells. Incorporation of 3 at% of phosphorous in the reactants of the free-space reactor used resulted in a doping level of 1.8 at%, a very high level of doping with regards to the standard in semiconductor silicon. However, even with this high level of doping, no significant effect was observed for cycling of silicon anodes using 60 wt% silicon. We propose that the benefit of doping silicon is masked by the effect of the conductive carbon and other additives used in preparation of the test cells.