Faradion (United Kingdom)

Sodium ion batteries offer a sustainable and low cost energy storage solution. In this talk we look atthe fundamental principles behind how they work at a materials, cell and battery pack level, as wellas some of the challenges that Faradion have overcome to successfully commercialise thetechnology.We also look at what the future holds, as global energy demand increases, where are the near andmid-term opportunities to deploy the technology, as well as the longer term outlook. Thepresentation will address the current state of the art in sodium-ion batteries, as well as what thefuture holds for the technology.

Sodium‐ion batteries (SIBs) are a promising grid‐level storage technology due to the abundance and low cost of sodium. The development of new electrolytes for SIBs is imperative since it impacts battery life and capacity. Currently, sodium hexafluorophosphate (NaPF6) is used as the benchmark salt, but is highly hygroscopic and generates toxic HF. This work describes the synthesis of a series of sodium borate salts, with electrochemical studies revealing that Na[B(hfip)4]⋅DME (hfip=hexafluoroisopropyloxy, OiPrF) and Na[B(pp)2] (pp=perfluorinated pinacolato, O2C2(CF3)4) have excellent electrochemical performance. The [B(pp)2]− anion also exhibits a high tolerance to air and water. Both electrolytes give more stable electrode‐electrolyte interfaces than conventionally used NaPF6, as demonstrated by impedance spectroscopy and cyclic voltammetry. Furthermore, they give greater cycling stability and comparable capacity to NaPF6 for SIBs, as shown in commercial pouch cells.

Bipolar electrodes can be defined as electrodes where cathode and anode active materials exist on either side of a shared current collector substrate. The resultant rechargeable bipolar batteries, using series-connected electrochemical cells within one sealed enclosure, can enable high-voltage systems irrespective of the voltage of the cathode//anode couple used. The sodium-ion battery, being well-suited for the bipolar concept, is now rapidly being commercialized and has higher energy densities than most rechargeable battery technologies. However, bipolar sodium-ion batteries using commercially-feasible liquid electrolytes and manufacturing methodologies, have not been demonstrated at scale yet. Herein, we explore the design methodology needed to enable commercial realization of such bipolar sodium-ion batteries, using liquid electrolytes and different types of cathode//anode couples. We show good cycling stabilities over 200 cycles and potential for voltages beyond 6 V for bipolar Na-ion pouch cells. We also introduce a scalable method to fabricate nSmP Na-ion/mixed-chemistry bipolar cells (n cells in series; m cells in parallel) in a single, sealed cell. Our results point to realistic promise for high voltage and sustainable bipolar sodium-ion batteries.

Faradion's business focus is concentrated on high-energy applications, such as large-scale energy storage systems, storage for renewables, uninterruptable power supply and low-cost electric vehicles where the cost reduction over Li-ion would be most apparent and thereby maximizing the cost benefit of this technology. The Faradion cell chemistry utilizes either an in-house prepared, or a commercially sourced, hard carbon as a negative electrode. One of Faradion's proprietary cathode materials is then used as the positive electrode. Faradion uses a proprietary electrolyte based on commercially available salts. The Faradion cell design enables versatile performance at various discharge rates. For global application of Faradion Na-ion cells, it is imperative that the cell chemistry must perform in different climates and regions. A three-electrode cell can provide invaluable information about the individual behavior of the cathode, anode and also the full cell in situ without disturbing the full cell's cycling performance.

The thinking behind Faradion's historical and current commercial Na-ion technology and the importance of some crucial experimental factors in battery research are discussed.

Sodium-ion (Na-ion) batteries represent an attractive alternative to their lithium-ion counterparts, and are expected to offer some significant commercial advantages such as lower active material costs and improved safety characteristics [1,2]. In these systems Na-based layered oxides, NaxMO2(M = transition metal) have emerged recently as high performance and low cost cathode materials [3,4]. These oxide materials may be categorized into three main structural types using the classification proposed by Delmas and co-workers – i.e. O3, P2 and P3 types, where the alkali ions occupy either octahedral (O) or prismatic sites (P), respectively [5].In this study single-phase O3-NaaNi(1-x-y-z)MnxMgyTixO2 materials have been prepared using conventional solid-state processing methods. In these as-made compositions nickel and magnesium are included as M2+ while manganese and titanium are present as M4+. Special attention was given to the product composition, precursor mixing and synthesis conditions to ensure no unwanted NiO impurity content. Figure 1 shows the XRD pattern for a typical O3-Na layered oxide composition and confirms that the material is essentially phase pure.The electrochemical performance of the experimental O3-NaaNi(1-x-y-z)MnxMgyTixO2 phases was evaluated in full Na-ion test cells where the cathode materials were capacity balanced to a commercial hard carbon anode material. The electrolyte used was 0.5 M NaClO4 in propylene carbonate and testing was carried out at 30 oC.In Figure 2 we depict the low rate (C/10) voltage profile derived from a typical constant current charge-discharge cycle. The cathode active material cycles reversibly at a specific capacity of 163 mAh/g and the Na-ion cell generates an average discharge voltage of around 3.0 V. The specific energy performance for the cathode is comparable to commercial Li-ion electrode materials.Figure 3 shows a typical cycle life plot for a representative Na-ion cell. These data were collected at a C/10 charge/discharge rate using voltage limits of 4.2 and 1.0 V. Following 300 cycles the cell has retained over 70 % of the original discharge capacity. Most of this capacity loss is recoverable at lower discharge rates indicating importantly that the fade mechanism is associated with cell impedance changes rather than irreversible loss of active Na. Further performance data for the Na-ion system will be presented.

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The Tavorite-type composition LiVPO4F undergoes a complex series of phase transformations upon Li+ electrochemical extraction or insertion at ∼4.25 V (V4+/V3+ redox couple) and 1.8 V vs. Li (V3+/V2+ redox couple), respectively. In all the reactions involved, followed by in-house in situ X-Ray diffraction, two-phase topotactic mechanisms are systematically encountered, without noticeable modification of the [VPO4F] framework besides significant unit-cell contractions/expansions and overall shifts in symmetry from triclinic P-1 to monoclinic C2/c. Two electrochemical oxidation reactions occur at 4.24 V and 4.28 V vs. Li due to the formation of the intermediate phase Li0.67VPO4F, isolated for the first time. Noticeably, this peculiar composition is not encountered upon reduction from VPO4F to LiVPO4F.