Sacrificial Salt Research Articles

Effect of Presodiation Additive on Structural and Interfacial Stability of Hard Carbon | P2‐Na0.66Mn0.75Ni0.2Mg0.05O2 Full Cell

AbstractThe compatibility between a corncob‐derived hard carbon anode and a layered oxide cathode (Na0.66Mn0.75Ni0.2Mg0.05O2), as well as the effect of presodiation via cathode additive (Na2C4O4), are investigated in a sodium‐ion full cell. Extensive physicochemical and electrochemical characterizations are performed to deeply investigate the structural and interfacial evolution of the materials in the presodiated cell, either within the single cycle or upon long‐term cycling. The use of sacrificial cathode additives is generally regarded as a method to improve full cell performance, especially when using sodium‐deficient materials. However, undesired effects upon decomposition of the sacrificial salt may arise due to the complexity of the system. In this study, it is evidenced that the presodiation changes the properties of the electrodes causing a worsening of the electrochemical performance of the cell during long‐term cycling. The surface morphology of the cathode is negatively affected by the formation of holes/cracks, while redox processes associated with structural transformations are suppressed in the voltage window of interest, with partial structural deformations occurring during activation cycles. The SEI and CEI are also affected by the formation of insulating organic species, which lead to an increased thickness and interphase resistance hampering the charge transfer kinetics of the cell.

On the Challenges to Develop Hybrid Faradaic‐Capacitive Electrodes Incorporating a Sacrificial Salt for Lithium‐ion Capacitors: The Case of Li3V1.95Ni0.05(PO4)3‐AC‐Li2C4O4

AbstractThe low capacity of activated carbon (AC) electrodes remains as one of the major limiting factors for the development of high energy density lithium‐ion capacitors (LICs). Hybridization of capacitive AC electrodes by incorporating faradaic materials into the electrode formulation could be performed to enhance the capacity of the overall device. However, this strategy requires an accurate electrode design to maximize the performance. In this work, Li3V1.95Ni0.05(PO4)3 (LVNP) was selected as faradaic material due to its compatibility with AC, showing high capacity, fast ionic diffusion, and relatively high conductivity. Various formulations and mass loadings have been studied to analyze the impact of incorporating LVNP into the positive electrode on the performance of the hybrid electrode. Moreover, for practical LIC applications, a sacrificial salt ‐dilithium squarate, Li2C4O4‐ was included in the hybrid electrode as a pre‐lithiation additive, developing a ternary electrode. The sacrificial salt oxidized releasing lithium ions, while the electrochemical performance of the hybrid positive electrode remained almost unaltered. Finally, a cycle life test combined with a post‐mortem analysis allows understanding the failure mechanisms of the electrode, suggesting the need of further improvements of the electrolyte and electrode‐electrolyte interface to develop long lifetime hybrid faradaic‐capacitive electrodes based on LVNP‐AC active materials.

Bending induced polarization charges in non-polar porous polymer for stroke rehabilitation

Owing to the flexibility, lightweight, long-life and low cost, polymers are promising candidates to realize electromechanical conversion in wearable electronics. The flexoelectric effect enables non-piezoelectric materials to achieve electromechanical coupling, thereby broadening application ranges of nonpolar polymers. In this work, the porous samples of polydimethylsiloxane (PDMS) with various pore sizes and porosities are fabricated by the sacrificial salt template method and the chemical gas foaming method. The flexoelectric polarization response can be tuned directly by the structural characters of the porous PDMS. The transverse flexoelectric coefficient of porous PDMS can reach approximately 2.9 times the counterpart of the bulk one. The competitive mechanism between strain gradient and permittivity is proposed on flexoelectricity of random porous media by dielectric impedance spectrums and finite element analyses. The present regulation of flexoelectricity provides an alternative to electromechanical conversion. With the deep learning technique based on one-dimensional convolution neural networks, actions of both sick and normal legs of various stroke patients can be well recognized by the designed device of rehabilitation. The present rehabilitation monitoring system, which is an innovative application of the flexoelectricity in the porous polymers, offers a new approach to support physical therapy for post-stroke patients.

Application of Na2CO3 as a Sacrificial Electrode Additive in Na‐ion Batteries to Compensate for the Sodium Deficiency in Na2/3[Fe1/2Mn1/2]O2

AbstractOwing to their high discharge capacities, P2‐type transition metal layered oxides have attracted attention for use as positive electrode materials in Na‐ion batteries. However, owing to the Na‐deficient compositions of these oxides, additional Na+ must be supplied using a Na‐metal negative electrode to attain a high capacity in a half‐cell configuration. In this study, solid Na2CO3 powder was introduced into the P2−Na2/3Fe1/2Mn1/2O2 composite positive electrode as a sacrificial salt to compensate for the Na deficiency. Na+ was supplied through the electrochemical oxidative decomposition of Na2CO3 during the initial charging process; the decomposition mechanism responsible for this process was investigated in detail. Online electrochemical mass spectrometry confirmed that Na2CO3 was oxidatively decomposed in combination with the decomposition of the ethylene carbonate electrolyte. This reaction produced CO2, wherein the carbon source was derived from both Na2CO3 and the electrolyte. Consequently, Na+ supplementation improved the reversible capacity of the Na‐ion full cell. This study offers practical insights and a mechanistic understanding of the pre‐doping technique for Na‐free negative electrodes. This approach also compensates for the irreversible reductive capacity in a process that can be easily applied to practical sodium‐ and lithium‐ion batteries and capacitors.

In Situ Crosslinked Gel Polymer Electrolytes for Li-Ion Capacitors

Supercapacitors are the choice when high-power performance is essential, however, for many applications the energy density of supercapacitors is too low to be used. To increase the energy density, it is possible to combine an insertion type anode of a Li-ion battery with a capacitor type double-layer electrode, forming a so-called Li-ion capacitor (LIC) [1]. There are however several issues with LICs that needs to be resolved to enable a more widespread use in applications. The most critical issue is the pre-lithiation of the anode, which can be either electrochemical or mechanical, this adds an extra processing step and increases the cost of assembly. Another issue is the stability at elevated temperatures and flammability of the organic electrolyte most often used in Li-ion capacitors. Recent progress dealing with the issue of lithiation of a hard carbon anode has been made by researchers at CIC energiGUNE, suggesting the use of a cheap and commercial dilithium squarate as a sacrificial salt [2]. For battery applications polymer electrolytes (PEs) have been suggested as a possible route to improve stability and increase the safety of the device. A similar approach using PEs could be used in LICs, but there are only a few publications for high power devices such as traditional supercapacitors [3]. Important properties of electrolytes in general for LICs are wide electrochemical stability window, high conductivity and a low viscosity to ensure a complete infiltration of activated carbon materials [4]. For a solid electrolyte to fulfill these demands the PE content should be low, the conductivity of the liquid component should be high and the electrolyte needs to be able to be crosslinked in situ, so that a PE can infiltrate and be formed throughout the electrodes of the cell. In this work, we have investigated a mixture of two monomers that can be covalently crosslinked as the polymer component in a EC:DMC based liquid electrolyte. This polymer mixture enables the formation of gel polymer electrolytes (GPEs) in situ, at very low concentrations, through the addition of an initiator and a mild heat treatment that enables the breaking of double bonds. Similar results have been shown in slightly different systems to provide a high conductivity and wide electrochemical stability windows [3][5]. In this work we show that the GPE does not affect the use of a sacrificial salt and that it would increase the safety of the device by eliminating the risk of leakage while maintaining the high-power performance of the LIC previously only showed for liquid electrolytes.

Sodium Mesoxalate as PRE-Sodiation Agent in Sodium-ION Capacitors

Lithium devices are the ones that reached the market to prompt the sustainable use of renewable sources, the alternative promise to leave behind fossil fuels dependency. However, lithium reservoirs seem not to be enough to supply the expected increase in future market demands. On account of that, the appearance of sodium-energy devices as an alternative to lithium is rising interest due to its abundance and easy availability. Those market demands are increasingly focused on delivering high energy and power density in a single device. These requirements lead to the appearance of Sodium-Ion Capacitors (SICs), which consist of a supercapacitor like cathode confronted with a battery like anode, extracting the main advantages of each technology, i.e, high energy stored, and power supplied as well as long cycle-life. Despite their potential, still some challenges need to be addressed to widespread their commercialization. The low coulombic efficiency of the first cycle together with the absence of a sodium source apart from that of the electrolyte, is the major challenge to ensure high energy densities without penalizing cycle life. A possible strategy is the addition of a pre-sodiation agent to the system [1]. Different agents have been tested so far, however an ideal solution has not been developed yet. In the present study sodium mesoxalate is suggested to be employed as pre-sodiation agent as it is a commercial, green and nontoxic compound [2].Herein, sodium mesoxalate was added directly to the positive electrode. The carbons C65 an Ketjen black (KB) were explored as conductive additives. Two different procedures of positive electrode fabrication were studied and in depth analyzed with the aim of extracting the best performance of the sacrificial salt. From this study it was found that the KB mixed with the monohydrated salt followed by a joint dehydration seems to extract the best performance of the sodium mesoxalate.To complete electrode manufacturing, YP50F was added as active material . The CV (Figure 1a) shows a single peak during the first cycle at around 4.25 V vs. Na+/Na, related to the decomposition of the Na2C3O5. This value is low enough to avoid electrolyte decomposition. In the second cycle, a little hump is also appreciated at ca. 3.6 V vs. Na+/Na probably due to a little remanent salt unable to be decomposed during the first cycle. In the following cycles, the voltammetries show a rectangular shape, attributed to the capacitance recorded by the electrode without the already decomposed salt, and mainly ascribed to the YP50F. Moreover, from the GA charge/discharge (Figure 1b) it can be seen that during the first charge, the sodium mesoxalate is able to provide a specific capacity of 405 mAh g-1 which is higher than the theoretical one (331 mAh g-1).Consequently, the results shown herein evidence the potential of the sodium mesoxalate as pre-sodiation agent in SICs as long as the proper conductive additive and obtention procedure are employed.[1] M. Arnaiz, D. Shanmukaraj, D. Carriazo, D. Bhattacharjya, A. Villaverde, M. Armand, J. Ajuria, A transversal low-cost pre-metallation strategy enabling ultrafast and stable metal ion capacitor technologies, Energy Environ. Sci. 13 (2020) 2441–2449. https://doi.org/10.1039/D0EE00351D.[2] A.J. Fernández-Ropero, M. Zarrabeitia, G. Baraldi, M. Echeverria, T. Rojo, M. Armand, D. Shanmukaraj, Improved Sodiation Additive and Its Nuances in the Performance Enhancement of Sodium-Ion Batteries, ACS Appl. Mater. Interfaces. 13 (2021) 11814–11821. https://doi.org/10.1021/acsami.0c20542. Figure 1

Roll-to-roll double side electrode processing for the development of pre-lithiated 80 F lithium-ion capacitor prototypes

Lithium-ion capacitors (LICs) show promise to help lithium-ion batteries (LIBs) and electrical double layer capacitors (EDLCs) in giving response to those applications that require an energy storage solution. However, pre-lithiation is a major challenge that needs to be tackled in order to develop efficient and long-lasting LIBs and LICs. In this work, we report for the first time the scale-up and utilization of sacrificial salts (dilithium squarate, Li2C4O4) as a pre-lithiation strategy in a LIC prototype fabricated in a pilot line. The synthesis of the sacrificial salt is scaled-up to produce 1 kg and is later incorporated in the positive electrode during the slurry formulation. After in-depth process optimization, 12 meter of a double side electrode are fabricated, achieving a high mass loading of 5.5 mg cm−2 for the HC negative electrode, and 14 mg cm−2 for the positive electrode accounting both the activated carbon and the dilithium squarate. On account of the satisfactory mechanical and electrochemical behaviour of the electrodes, multilayer pouch cell LIC prototypes are fabricated reaching 80 F each. Pre-lithiation is completed during the first ten cycles and after the required gas exhaustion, electrochemical performance of prototypes is also satisfactory. Moreover, fabricated pouch cells overcome a float test of 1600 h at 50 °C showing a capacitance retention of 84.3%. These results give clear evidence for the potential use of this strategy in real products and can foster research in the field to promote pre-lithiation by means of sacrificial salts as the final solution to the pre-lithiation step, both for LIBs and LICs.

Degradation Mechanisms of Positive Electrode Materials for Sodium-Ion Batteries

Sodium-ion batteries (SIB) require less critical materials and lead to a significant cost reduction compared to state-of-the-art lithium-ion batteries [1]. Although a large-scale commercialization of SIBs is within reach [2], the understanding of the degradation mechanisms of these batteries is still incomplete. The larger ionic radius of sodium in comparison to that of lithium can induce larger stress changes in the host material causing poor long-term stability. Minimizing degradation of positive electrode materials is of high importance for the advancement of SIB technology. Here, we report on degradation of the important structure types: layered oxides, polyanionic compounds, and Prussian blue analogues. Our results show that the polyanionic Na3V2(PO4)3 is a highly reliable cathode material, which can be used as a benchmark or reference material.During battery operation, mechanical stresses are caused by volume changes of the active materials, when sodium ions are inserted or extracted into/from them. We use operando methods such as the substrate curvature technique to measure stresses in the electrode and draw conclusions about electrochemical and physical processes in the materials during cycling [3]. To investigate phenomena like volume changes, crack formation and overall morphology, ex situ scanning electron microscopy (SEM) is used intermittently. Here, we compare the same site on the electrode in different states of charge and for different cycle numbers. Additionally, X-ray diffraction (XRD) measurements are conducted to study phase transitions.Na2/3Fe1/3Mn2/3O2 is a layered P2-type oxide that offers a high specific capacity and is composed of abundant elements. Due to its intrinsic sodium deficiency, diverse presodiation methods become important [4]. We investigate Na2C4O4 as sacrificial salt and its effects on electrode morphology during decomposition. Our goal is to understand the resulting reaction pathways and optimize the full cell performance of layered oxides.Sodium hexacyanoferrate NaxFe[Fe(CN)6] is a Prussian blue analogue and one of the most prominent candidates for commercial SIBs [2]. It also offers high specific capacities and a long cycle life, but its high moisture sensitivity and interstitial water demand appropriate electrode drying procedures to avoid side reactions during cell operation. Crack formation and growth were studied with SEM after and during cycling. Phase transitions are observed by operando XRD and operando substrate curvature measurements.Sodium vanadium phosphate Na3V2(PO4)3 (NVP) with its highly stable three-dimensional network of a NASICON-type structure and its large diffusion channels for sodium ions is another promising electrode material that deserves attention. NVP can be sodiated and desodiated at two different voltage plateaus and therefore can serve either as cathode or anode material. SEM observations at different states of charge show how preexisting cracks open/close during desodiation/sodiation due to volume shrinkage/expansion. We compare symmetric NVP−NVP cells to full cells with NVP cathodes and anodes of Na metal, hard carbon, Sb/C, and SnSb/C. Our data suggests that problems of Na and Na-ion cells frequently result from the anode. NVP itself is extremely reliable and balanced symmetric NVP−NVP cells exhibit very high cycling stability. More than one thousand cycles can be easily achieved. Due to its distinct plateaus and high stability, we suggest NVP as a reference material for cathode and anode materials. For example, NVP can serve as a reliable anode material for testing the stability of different cathode materials. NVP as a cathode may be used to test anode materials or as a benchmark for other cathode materials [5].Acknowledgements:This work contributes to the research performed at CELEST (Center for Electrochemical Energy Storage Ulm-Karlsruhe) and was funded by the German Research Foundation (DFG) under Project ID 390874152 (POLiS Cluster of Excellence, EXC 2154).Literature:[1] C. Vaalma et al., Nature Reviews Materials 2018, 3, 4, 1-11.[2] M. A. Sawhney et al., ChemPhysChem 2022, 23, 5, 1-19.[3] Z. Choi et al., Journal of Power Sources 2013, 240, 245-251.[4] J. M. De Ilarduya et al. Electrochimica Acta 2019, 321, 134693.[5] T. Akçay et al., ACS Applied Energy Materials 2021, 4, 11, 12688-12695.

Enabling versatile, custom-made lithium-ion capacitor prototypes: Benefits and drawbacks of using hard carbon instead of graphite

In this work, the benefits and drawbacks of replacing graphite by hard carbon as negative electrode in a lithium-ion capacitor are studied. Beyond the material selection and electrode optimization, the impact of the cell design in the final performance is also evaluated. When selecting hard carbon, final prototype avoids using any critical raw material, since a sacrificial salt (dilithium squarate) has been also used as a pre-lithiation strategy, instead of the most preferred industrial metallic lithium-based solution. The combination of these two strategies shows unique features, enabling the development of a highly sustainable, easy-to-recycle, eco-friendly energy storage solution, towards a more realistic approach. Likewise, this solution offers high versatility and degree of freedom to tune the mass loading, mass balance and operating voltage, enabling custom-made prototypes, offering a large portfolio of products, owing to the electrochemical characteristics of hard carbon. Prototype's internal components design determines final cell performance, which it is directly related to the equilibrium between the most relevant metrics, i.e., energy, power and cyclability. Thus, smart ad-hoc designs can be developed to cover a wide range of applications and specific needs of different market niches. Full performance analysis for different-in-design monolayer pouch cells that can operate beyond 4.0 V is reported in this work.

A presodiation strategy with high efficiency by utilizing low-price and eco-friendly Na2CO3 as the sacrificial salt towards high-performance pouch sodium-ion capacitors

Sodium-ion capacitor (SIC) bridges the gap between sodium-ion battery (SIB) and supercapacitor (SC). It can exhibit high energy density than SC and deliver high power density and cyclic property than SIB. However, the advancement of SIC is restricted by presodiation. We present a presodiation strategy with high efficiency for pouch SIC by utilizing low-price and eco-friendly Na 2 CO 3 as the presodiation material. With a high capacity utilization (82.6%), Na 2 CO 3 displays a specific capacity of 417.1 mAh g −1 . The constructed pouch SIC with Na 2 CO 3 as the presodiation material exhibits a superior performance: 103 Wh kg −1 , 13 kW kg −1 and a capacitance retention of 84.5% after 2000 cycles. • A presodiation strategy is presented by utilizing Na 2 CO 3 as the sacrificial salt. • The presodiation strategy is facile, high-efficiency, low-price and eco-friendly. • Na 2 CO 3 /AC electrode has a higher Na 2 CO 3 decomposition rate than Na 2 CO 3 electrode. • The constructed sodium-ion capacitor exhibits outstanding performances.

Pre-lithiated TiSb2 alloy-based lithium-ion capacitor exceeding 20000 cycles and standing for more than 1000 hours of float time

The dream of using beyond-carbon metalloids or transition metals as anode materials in electrochemical energy storage systems has been long pursued for the sake of greater capacity. However, two major challenges remain unresolved: the high volumetric expansion suffered by those materials, causing severe mechanical stress ending up in device failure, and the large first cycle irreversibility. In this work, we tackle both in a single approach, by using titanium to buffer mechanical stress of antimony (TiSb 2 ) and by adopting the recently proven dilithium squarate sacrificial salt (Li 2 C 4 O 4 ) strategy to pre-lithiate the system. Overall, herein developed alloy-based lithium-ion capacitor (LIC) demonstrates between double and triple volumetric performance respect to a dual carbon LIC. Moreover, the system is shown to be stable over 20000 cycles and 1000 h of floating at 3.8 V and room temperature. Post-mortem analysis correlates the origin of failure to the electrolyte oxidation and not to the degradation of the alloying material itself. Re-assembled TiSb 2 , AC, and full device with fresh electrolyte show to almost perform as good as the originals. • Lithium-ion capacitor based on alloying TiSb 2 and activated carbon. • TiSb 2 is pre-lithiated by using a sacrificial salt, namely, Li 2 C 4 O 4 . • LIC is stable over 20000 cycles. • LIC is stable over 1000 h floating at 3.8V. • Post-mortem analysis reveals electrolyte degradation to be the source of failure.

Development of a Li-Ion Capacitor Pouch Cell Prototype by Means of a Low-Cost, Air-Stable, Solution Processable Fabrication Method

Due to the dual advantage of capacitive and faradaic charge storage mechanisms, Li-ion capacitors (LICs) are regarded as a promising energy storage technology for many high-power applications. However, high cost and intricacy of indispensable pre-lithiation step in LIC fabrication are the major stumbling block against its widespread commercial interest. In this regard, operando pre-lithiation through incorporating lithium containing sacrificial salt in the positive electrode holds high potential to solve this issue. Herein, we present an industrially compatible fabrication method based on a solution processable positive electrode consisting of an activated carbon mixed with a low-cost, air-stable dilithium squarate as sacrificial salt. Through careful optimization of electrode design, laboratory scale cells are upscaled to pouch cell prototypes. Fabricated LIC pouch cells deliver high specific energy (i.e. max. 58 Wh kg−1 AM) and power (i.e. max. 8190 W kg−1 AM) with respect to active electrode mass. Moreover, cycle life and floating tests performed at room temperature show capacitance retention of 83% after 80000 charge-discharge cycles and 100% retention after 1000 floating hours at 3.8 V. However, the accelerated aging tests at 70 °C induce fast device failure. Post-mortem analyses reveal different ageing mechanisms for cycled and floated LIC pouch cells.

(Invited) Sodium Layered Oxides in the Spotlight: Current State-of-Art and Remaining Challenges

The development of new energy storage technologies is essential for the advancement of a society increasingly dependent on energy supplies. In this context, sodium-ion batteries (SIBs) have proven to be the key to revolutionizing the global energy market, especially for large-scale stationary energy storage and light electromobility [1]. However, the achievement of the full potential of SIBs technology remains a challenge and efforts should be focused on the design of more efficient high energy density and high cycle life sodium-based positive electrodes. In this scenario, sodium-based layered oxide cathodes with general formula NaxMO2 (M = transition metal/s) are an excellent choice due to their electrochemical performance, environmental friendliness and scalability [2,3]. Prof. Claude Delmas pioneered the study of the electrochemical intercalation processes of this family of compounds, being one of the first researchers to exploit their potential in SIBs. Although the virtues of this family of materials as cathodes are clear, there are also several drawbacks such as irreversible structural phase transitions, strong Na+-vacancy ordering tendencies or poor cyclability that should be addressed to ensure the optimum operation of this material in a commercial battery.One of the peculiarities of these cathode materials lies in the diverse structures that they can adopt, being the P2 and O3 structures the most interesting from the electrochemical point of view. P2-type phases present higher rate performance and capacity retention than O3-type phases. However, they are only stable with sodium contents ≤ 0.85, which translates into higher first irreversible capacity. In O3-type phases, on the other hand, it is possible to reach the fully sodiated stoichiometry, delivering thus higher capacities but at the expense of considerable retention nested in O3-P3 phase transitions, which alter the diffusion mechanism of Na+ ions giving rise to a large energy barrier that Na+ ions must overcome.This talk will present the main advances on the development of sodium layered oxide cathodes, as well as the most successful strategies for overcoming current challenges, such as doping with electrochemically active and inactive elements [4], surface coatings [5], the use of sacrificial salts [6] or the synergetic P2/O3 combination effect [7]. Finally, the anionic redox effect and the controversy in the explanation of the extra capacity observed in certain de-sodiated transition metal oxides will also be discussed. Goikolea, T. Rojo, et al. Adv. Energy Mater. 2020, 10, 2002055H. Han, T. Rojo, et al., Energy Environ. Sci. 2015, 8, 81–102Ortiz-Vitoriano, T. Rojo, et al., Energy Environ. Sci. 2017, 10, 1051–1074Gonzalo, T. Rojo, et al. Enegy Storage Mater. 2021, 34, 682–707Zarrabeitia, T. Rojo, et al. J. Mater. Chem. A, 2019, 7, 14169–14179J. Fernández-Ropero, D. Shanmukaraj et al. ACS Appl. Mater Interfaces, 2021, 13, 11814–11821Bianchini, T. Rojo, et al. J. Mater. Chem. A, 2018, 6, 3552–3559.

A safe, low-cost and high-efficiency presodiation strategy for pouch-type sodium-ion capacitors with high energy density

Sodium-ion capacitors (SICs) have attracted appreciable attention in virtue of the higher energy and power densities compared with their rivals, supercapacitors and sodium-ion batteries. Due to the lack of sodium resources in cathode, presodiation is critical for SICs to further augment performances. However, current presodiation strategy utilizes metallic sodium as the presodiation material. In this strategy, assembling/disassembling of half-cells is required, which is dangerous and increases the time and cost of SIC leading to the restriction of their industrialization and commercialization. Herein we present a safe, low-cost and high-efficiency presodiation strategy by first employing Na2C2O4 as the sacrificial salt applied in SICs. Na2C2O4 is environmentally friendly and possesses considerably low expenditure. No additional residues remain after sodium extraction ascribed to its “zero dead mass” property. When paired with commercial activated carbon as the cathode and commercial hard carbon as the anode, the constructed pouch-type SICs exhibit high energy and power densities of 91.7 Wh/kg and 13.1 kW/kg, respectively. This work shows a prospect of realizing the safe and low-cost manufacturing for high-performance SICs commercially.

(Invited) A Transversal Low-Cost Pre-Lithiation Strategy Enabling Ultrafast and Stable Lithium Ion Capacitors

Lithium ion capacitors (LICs) are foreseen to be a complementary alternative of vital importance to current energy storage issues, coupling high energy density delivered by batteries with high power/long cycle life offered by supercapacitors. The prime issues in realising this technology are pre-lithiation and replacement of graphite electrodes that bring about energy gain at the expense of power. Herein we present an easy-to-scale-up approach, combining activated carbon with a highly efficient and industrially compatible low-cost sacrificial salt (dilithium squarate), that can be used as a lithium source for pre-lithiation. Paired with a hard carbon electrode tailored to perform at high rates, a LIC is demonstrated. Furthermore, the successful fabrication of a LIC pouch cell prototype with high energy at high power densities showing capacitance retention over 84% after 48000 cycles validates the strategy. This breakthrough may trigger the easy and low-cost fabrication of LICs and significantly reduce technological barriers to market growth and consolidation. Figure 1. Scheme representing the pre-metallation strategy followed in this work: Open circuit) MICs are represented by pristine HC as the negative electrode, each electrolyte corresponding to LIC, NIC and KIC with cations represented in dark blue (Li+), dark red (Na+) and dark green (K+) while anions are represented in brown (ClO4 -) and grey (PF6 -), and AC combined with the sacrificial salt -whose ions are represented in light colors- as the positive electrode; 1st charge) Cations from electrolyte and sacrificial salt are inserted into the HC while PF6 - anions are adsorbed into the AC surface; 1st discharge) While the excess of cations coming from the sacrificial salt are permanently inserted into the HC to compensate for the first cycle irreversibility (light colored cations), cations from electrolyte are reversibly inserted/deinserted as well as anions are adsorbed/deadsorbed allowing MICs to operate efficiently. Figure 1

Printable Lithium Technology for Pre-Lithiation and Solid-State Battery Applications

The need for pre-lithiation has become more important due to the commercialization of anodes containing silicon for high energy density batteries. When Si / Graphite mixtures are used, there can be 10-20% or higher active lithium loss on the first charge depending on the amount of Si used. Pre-lithiation can introduce sacrificial lithium into a lithium ion cell which will off-set the irreversible lithium loss. There are many proposed pre-lithiation techniques such as roll-to-roll electrochemical baths, sacrificial salts, vacuum deposition and lithium sputtering. (1) None of these pre-lithiation methods have been scaled beyond the laboratory or pilot scale due to safety, cost, manufacturing inefficiencies or cell performance issues. Currently, the pre-lithiation method that has shown the most promise is the addition of lithium metal to the prefabricated anode (2), (3), (4). Because of its high capacity, lithium metal causes a negligible increase in cell mass and volume. In comparison, when sacrificial salts are used, the energy density can decrease due inactive phases remaining after lithium extraction.One solution has been to use stabilized lithium metal powder (SLMP®) to pre-lithiate silicon-based anodes (5), (6). The use of Livent’s advanced material, Lectro® Max Powder (SLMP) has been demonstrated worldwide as an effective and efficient pre-lithiation material (7). SLMP can deliver capacity close to the theoretical lithium capacity of 3860 mAh/g and, after addition of the electrolyte, it intercalates or alloys with the anode material in-situ, and; therefore, exists in the lithium ion form in the cell. By incorporating this sacrificial source of lithium in the anode to compensate for first cycle irreversible losses, the lithium provided by the cathode can be fully utilized.The use of dry SLMP in large scale deployments presents challenges that have delayed wide-spread adoption of the technology. To this end, Livent has developed a proprietary technology that incorporates SLMP into a stable printable formulation. Printable Lithium Technology (PLT) is uniquely positioned to address challenges associated with handling of a high surface area reactive powder; thus, allowing to mitigate both industrial hygiene and process safety issues. Printable Lithium Formulation (PLF) is comprised of SLMP dispersed in a compatible solvent along with other rheology and performance modifiers to create a formulation that is chemically stable and not prone to separation for extended periods of time. The solvent used is compatible with commercial electrode slurry solvent removal and recovery practices and is less toxic than NMP. The technology is easily scalable using industry standard coating and printing equipment to apply the formulation to the surface of a prefabricated anode. PLT is adaptable to any anode or cathode chemistry where an independent source of lithium is required. PLT can be used in anodes with a range of silicon content, because lithium loading can be accurately controlled based on the applications’ requirements. Lithium loading control is achieved through modification of the print head to print stripes of various width and spacing on the electrode surface. The patterns can range from narrow stripes spaced evenly across the electrode to a monolithic lithium layer. F igure 1. Cycle performance for commercially available electrode materials with anode loading > 4mAh/cm2. A) NMC811/Graphite-10% SiO; B) NCA/Graphite-10% SiO, C) LCO/80% SiO Composite; D) LFP/Hard carbon. Cycling condition: A and B: CCCV (0.5C rate with charge current cut off 0.1C), 2.8-4.2V at RT. Every 50th cycle is at C/10 rate. C: 2.8-4.45V, 0.1C-0.1C at RT. D: 2.5-3.5V, 0.1C-0.1C at RT. References Florian Holtstiege, Peer Bärmann, Roman Nölle, Martin Winter, and Tobias Placke, Pre-Lithiation Strategies for Rechargeable Energy Storage Technologies: Concepts, Promises and Challenges, Batteries 2018, (491), 4Sa Li, Yunhui Huang, Ju Li et al., Roll-to-roll prelithiation of Sn foil anode suppresses gassing and enables stable full-cell cycling of lithium ion batteries. Energy Environ. Sci., 2019,12, 2991Chengxu Shen, Rusheng Fu, Yonggao Xia and Zhaoping Liu, New perspective to understand the effect of electrochemical prelithiation behaviors on silicon monoxide. RSC Adv.,2018,8, 14473Michael W. Forney, Matthew J. Ganter, Jason W. Staub, Richard D. Ridgley and Brian J. Landi, Prelithiation of Silicon−Carbon Nanotube Anodes for Lithium Ion Batteries by Stabilized Lithium Metal Powder (SLMP). doi.org/10.1021/nl401776d, NanoLett.R. Jarvis, M.J. Lain, Y. Gao, and M. Yakovleva, J. Power Sources, 146, 331 (2005).Li, B. Fitch, Electrochem. Commun., 13, (2011) 664.Guo Ai, Zhihui Wang, Hui Zhao, Wenfeng Mao, Yanbao Fu, Vincent Battaglia, Sergey Lopatin, and Gao Liu, Scalable process for application of stabilized lithium metal powder in Li-ion batteries. Journal of Power Sources, (2016). Figure 1

Battery prelithiation enabled by lithium fixation on cathode

Li3N in the form of powder as the most appealing sacrificial salt has already been investigated for prelithiation, yet not been widely acknowledged due to its incompatibility with common solvents to a great extent. Herein, we report an unexpected way by depositing metal lithium directly on cathode surface and then fixing it by nitrogen gas to synthesize pure alpha-Li3N film with (001) plane perpendicular to surface. Moreover, its decomposition pathway along the direction from the surface to the inner cathode is revealed. After being used to compensate the lithium loss in LiFePO4/graphite full cell, discharge capacity at 120th cycle has raised by 30.7% with 1% Li3N coating. Apart from that, this kind of Li3N film has successfully served as the sole lithium source to fabricate full-cell with TiS2 and graphite as electrodes, in which 142.4 mAh g−1 of capacity can remain after 50 cycles. In short, the introducing/expelling of nitrogen for Li fixation/Li+ release is a facile strategy to realize battery prelithiation with easy preparation and high efficiency.

Cathode properties of FeF3–V2O5 Glass/C for lithium-ion batteries

For large storage batteries, cost performance is more important than energy density. Iron-based conversion-type cathode active materials are promising because this material group satisfies both low-cost and high-capacity requirements. In particular, iron fluoride is notable for its relatively high discharge voltage. However, the electronic conductivity of FeF3 is poor and it has large discharge-charge overvoltage. To solve these issues, xFeF3-V2O5/C (9xFeF3-9V2O5–P2O5) was investigated and the composition with x = 2 was shown to be optimal. Furthermore, the cyclability of 2FeF3–V2O5/C was improved by changing the salt from LiPF6 to LiClO4 and changing the solvent from DMC to EMC. Although the V2O5 glass component showed irreversible capacity due to Li trapping in the glass matrix at the first cycle, the irreversible capacity at the first cycle was successfully compensated by the addition of LiF as a sacrificial salt.

A transversal low-cost pre-metallation strategy enabling ultrafast and stable metal ion capacitor technologies

A low-cost pre-metallation strategy based on inorganic sacrificial salts that decompose on the first charge.

Controllable Charge Capacity Using a Black Additive for High-Energy-Density Sodium-Ion Batteries

Introduction Sodium-deficient P2 or P′2 type layered materials are known to deliver high capacity with acceptable capacity retention. However, the initial charge capacity is substantially lower than the discharge capacity because of the insufficient amount of sodium in their crystal structure, hindering practical application of these materials as cathodes in sodium-ion batteries (SIBs). This limitation can be overcome by introducing a sacrificial salt additive, which participates in the electrochemical oxidation reaction by releasing enough sodium ions to compensate for the insufficient sodium content in the cathode material. Herein, the sacrificial salt NaNO2 was blended with a high-capacity orthorhombic P′2 type Na2/3[Co0.05Mn0.95]O2 cathode material, increasing the initial charge capacity from 154 to 210 mA h g-1. During electrochemical oxidation, the NaNO2 was oxidatively decomposed by the following reaction: NaNO2 → NO2 + Na+ + e-, where NO2 is an oxidizer that enables full desodiation to Na0[Co0.05Mn0.95]O2. The first coulombic efficiency of Na2/3[Co0.05Mn0.95]O2 was improved from 1.38 to 0.98 by virtue of the sacrificing and oxidizing roles of NaNO2. Experimental P’2-type layered Na2/3[Co0.05Mn0.95]O2 was synthesized via spray pyrolysis. Stoichiometric amounts of manganese nitrate tetra-hydrate, cobalt nitrate hexahydrate, and sodium nitrate were dissolved in distilled water at 25 °C. Citric acid as a chelating agent and sucrose as a particle agglomeration inhibitor were added to the prepared aqueous solution at a molar ratio of the starting material : citric acid : sucrose of 1 : 0.2 : 0.05. The concentration of the starting solution was 0.08 M. The resulting aerosol stream was introduced into a vertical quartz reactor heated to 400 °C. The as-received precursor powders were calcined at 1200 °C for 10 h in a furnace in a dry air atmosphere with a flow rate of 300 mL min-1 and subsequently cooled to 25 °C. NaNO2 was intimately blended with the conducting agents by ball-milling at a weight ratio of 1 : 1, yielding a black-colored powder. The as-synthesized Na2/3[Co0.05Mn0.95]O2 and the mixture of NaNO2 and conducting agents were homogeneously blended in an agate mortar. Results and Discussion The introduction of a sacrificing agent, NaNO2, into sodium-deficient P2- and P’2-type layered cathode materials helped to overcome their intrinsic drawback of low charge capacities. The additive caused the release of additional sodium ions during electrochemical oxidation, which, in turn, provided additional capacity upon charging, bringing the first charge capacity closer to the discharge capacity. As a result, a high energy density of approximately 300 Wh kg-1 (calculated based on the cathode material) was achieved for the NaNO2/Na2/3[Co0.05Mn0.95]O2//hard carbon full cell. Supplementary experimental studies revealed that additional sodium ions were intercalated into the hard carbon. Hence, the high-capacity P’2 layered cathode can be used as a cathode material for high-energy-density SIBs. Details will be mentioned at the conference site. Figure 1