Conductive Carbon Additives Research Articles

Bucky-Si-Bucky Sandwiched Structured Anode for Li-Ion Battery

Silicon anodes have been of great interest due to their higher theoretical capacity (4200 mAh/g) compared to traditional graphite electrodes (~372 mAh/g). Although Si has a higher capacity, its full potential has not yet been realized due to pulverization of Si anode upon lithiation. Conventionally, Si anodes are made by casting a slurry consisting of Si powder, conductive carbon additives, and a binder on a Cu foil. In such anodes, pulverization of Si particles leads to film delamination from Cu foil ensuing in battery failure. To overcome this challenge, we developed a new sandwich-structured anode by encapsulating ~100 nm Si nanoparticles in between two porous carbon nanotube buckypapers. The buckypaper is a conductive porous structure, which can incorporate active material better than Cu foil facilitating increased mass loading. More importantly, this sandwich-structured anode provides improved electrical contact even under repeated pulverization of Si nanoparticles leading to higher cyclability. We were able to achieve capacities as high as ~700-1200 mAh/g with a stable performance for >100 cycles.

Enabling High-Rate Mn Oxide Pseudocapacitors Using Highly Dispersed Mn3O4 Nanocrystallites

Mn oxides are promising electrode materials for supercapacitors applications. They provide the advantages of high specific areal capacitance and densities, which are beneficial to achieving high device energy density. Nevertheless, they have so far demonstrated insufficient current rate performance, which is related to their poor electronic conductivities. Indeed, the establishment of a conductive network that is capable of efficiently connecting the nano-sized oxide particles within the electrode is essential to giving high current rate capability. In this work, we investigated the interplay between the Mn oxide particle properties and those of carbon conductive additives on the rate performance of the Mn oxide pseudocapacitor electrodes. The investigation adopts Mn3O4 as an example. Mn3O4 nano-crystallite powders having the same primary crystal size but varied agglomeration at the nano-meter scale were synthesized by a novel controlled solution oxidation process. The oxide powders were matched with carbon additives of different morphologies and dimensionalities for constructing electrodes having various electric networking configurations. The correlation between the rate performance of the oxide electrodes and the powder properties of both the oxide and the carbon additives is addressed. In particular, it is demonstrated that remarkable rate performance, along with superb cycle stability, is achieved with highly dispersed oxide nano-crystallites with zero-dimension carbon black additive. The results are important to the architecture design for oxide-based pseudocapacitors. Figure 1

Fabrication and Characterization of Thick Sintered Lithium-Ion Battery Full Cells

Commercial battery electrodes are composites containing electroactive material and inactive material – typically carbon conductive additives and polymer binders. Eliminating the inactive components would increase the energy density at the cell level. In addition, processing the electrodes to be thicker would improve energy density. One way to achieve both these goals is to fabricate thick electrodes comprised of only sintered active material. Such electrodes have not been extensively investigated, in particular in full cell configurations. Sintered electrodes have very high energy density, but they have relatively low electronic conductivity and longer ion diffusion pathways. Understanding the limitations and designs of these electrodes is the focus of this presentation. Li4Ti5O12 (LTO)/LiCoO2 (LCO) full cells with sintered electrodes were produced via custom synthesis, processing, and fabrication steps. The net movement of lithium was tracked using neutron imaging during electrochemical charge and/or discharge. The neutron imaging resulted in clear observation of the net movement of lithium in the cells. The neutron images provided insights into the lithiation and delithiation processes with different electrode thicknesses and different rates of discharge. The neutron imaging results were compared to electrochemical models of the discharge of the cell. The changes in concentration calculated using the model had good overall agreement with the neutron imaging observations, although improvements to the technique and model inputs will be discussed.

MIL-53(Al)/Carbon Films for CO2-Sensing at High Pressure

Chemiresistive threshold sensor films based on the switchable metal–organic framework (MOF) MIL-53(Al) (MIL = Materiaux de l’Institut Lavoisier) and conductive carbon additives were developed, char...

Four-Dimensional Studies of Morphology Evolution in Lithium–Sulfur Batteries

Lithium sulfur (Li–S) batteries have great potential as a successor to Li-ion batteries, but their commercialization has been complicated by a multitude of issues stemming from their complex multiphase chemistry. In situ X-ray tomography investigations enable direct observations to be made about a battery, providing unprecedented insight into the microstructural evolution of the sulfur cathode and shedding light on the reaction kinetics of the sulfur phase. Here, for the first time, the morphology of a sulfur cathode was visualized in 3D as a function of state of charge at high temporal and spatial resolution. While elemental sulfur was originally well-dispersed throughout the uncycled cathode, subsequent charging resulted in the formation of sulfur clusters along preferred orthogonal orientations in the cathode. The electrical conductivity of the cathode was found not to be rate-limiting, suggesting the need to optimize the loading of conductive carbon additives. The carbon and binder domain and surround...

Stretched to the Limit for Better Batteries

Conventional polymeric binders used within Li-ion battery electrodes cannot withstand the large volume changes exhibited by high-capacity alloying anode materials such as silicon, resulting in fast capacity decay with cycling. In this issue of Joule, Xu and coworkers report a new cross-linked polymer binder that enables excellent capacity retention over hundreds of cycles in silicon microparticle-based electrodes. To achieve this performance, this binder strongly adheres to the silicon while also exhibiting substantial mechanical elasticity and self-healing functionality.

Aromatic Polyimide Based Composites for Ultrafast and Sustainable Lithium Ion Batteries

Although lithium-ion batteries based on inorganic cathodes have been utilized in a wide range of applications, they still face challenges such as safety, power density and sustainability. Thus, efforts have been directed to look for alternative, greener and naturally abundant electrode materials for application in lithium ion batteries. As a result, different organic electrodes have been intensively investigated. Among them, aromatic polyimide is a very promising candidate with a theoretical capacity approaching 400 mA h g-1 and a working voltage around 2.5 V vs. Li/Li+. During the discharge process (lithium intake), aromatic polyimide can stepwise accept two electrons, resulting in the formation of a delocalized radical anion and dianion. Currently, there are two common issues preventing the practical application of aromatic polyimide. One is poor rate capability due to their low electronic conductivity and the other one is the rapid capacity fading during cycling due to the dissolution of the active organic cathodes. To overcome the intrinsic electrical insulation of aromatic polyimides and obtain high rate performance, highly conductive carbon additives such as graphene or carbon nanotubes and electron conductive polymers were used to make the polyimide composites. The effect of the type and the amount of conducting agents on the rate performance and long cycling stability of the aromatic polyimide composites based lithium ion batteries will be presented.

Effect of conductive carbon additives on electrochemical performance of LiCoPO4

The effect of conductive carbon additives (acetylene black with various specific surface areas and ketjen black) on the electrochemical performance of LiCoPO4 is investigated to develop 5 V-class lithium-ion batteries with good cyclability. The irreversible reactions between electrolyte and LiCoPO4 electrode can be kept small in addition to realizing reversible and a small amount of intercalation/deintercalation of PF6− into/from the graphite structure of carbon when using acetylene black with a low surface area as a conductive additive. However, the low surface area reduces the utilization of LiCoPO4, and degrades its cycle performance owing to the decrease of contact area between LiCoPO4 and carbon during charge and discharge cycles. On the other hand, ketjen black with a high surface area enhances the capacity of LiCoPO4, while it induces a large amount of irreversible reactions and the anion intercalation, leading to the rapid capacity fading. By using acetylene black with a moderate surface area as a conductive additive for LiCoPO4 electrode, the superior cycle performance can be achieved, which is attributed to the formation of good conductive network among LiCoPO4 particles by the carbon additive with an appropriate surface area to minimize the irreversible decompose reactions of electrolyte and the anion intercalation.

Dynamic behaviour of interphases and its implication on high-energy-density cathode materials in lithium-ion batteries

Undesired electrode–electrolyte interactions prevent the use of many high-energy-density cathode materials in practical lithium-ion batteries. Efforts to address their limited service life have predominantly focused on the active electrode materials and electrolytes. Here an advanced three-dimensional chemical and imaging analysis on a model material, the nickel-rich layered lithium transition-metal oxide, reveals the dynamic behaviour of cathode interphases driven by conductive carbon additives (carbon black) in a common nonaqueous electrolyte. Region-of-interest sensitive secondary-ion mass spectrometry shows that a cathode-electrolyte interphase, initially formed on carbon black with no electrochemical bias applied, readily passivates the cathode particles through mutual exchange of surface species. By tuning the interphase thickness, we demonstrate its robustness in suppressing the deterioration of the electrode/electrolyte interface during high-voltage cell operation. Our results provide insights on the formation and evolution of cathode interphases, facilitating development of in situ surface protection on high-energy-density cathode materials in lithium-based batteries.

Favorable Carbon Conductive Additives in Li3PS4 Composite Positive Electrode Prepared by Ball-Milling for All-Solid-State Lithium Batteries

A sulfide Li3PS4 (LPS) solid electrolyte is reversibly oxidized and reduced by mixing carbon additives in all-solid-state cells. Because LPS is an electronic insulator similar to S and Li2S, LPS functions as an active material at an interface between LPS and carbon. In this study, composite electrodes composed of LPS and one of various carbon conductive additives were prepared by ballmilling to investigate electrochemical performances of LPS, electrical effective conductivities, and a contact area between LPS and carbon in the LPS-carbon composite electrodes. The rate performance of all-solid-state cells with LPS-carbon composite electrodes was mainly affected by the ionic effective conductivity and the contact area of the composite electrodes. In various carbons, activated carbon was the most promising carbon to achieve the high electrical effective conductivities and the large contact area in the LPS-carbon composite electrode prepared by ballmilling.

Reversible Capacity of Conductive Carbon Additives at Low Potentials: Caveats for Testing Alternative Anode Materials for Li-Ion Batteries

The electrochemical performance of alternative anode materials for Li-ion batteries is often measured using composite electrodes consisting of active material and conductive carbon additives. Cycling of these composite electrodes at low voltages demonstrates charge storage at the operating potentials of viable anodes, however, the conductive carbon additive is also able to store charge in the low potential regime. The contribution of the conductive carbon additives to the observed capacity is often neglected when interpreting the electrochemical performance of electrodes. To provide a reference for the contribution of the carbons to the observed capacity, we report the charge storage behavior of two common conductive carbon additives Super P and Ketjenblack as a function of voltage, rate, and electrolyte composition. Both carbons exhibit substantial capacities after 100 cycles, up to 150 mAh g−1, when cycled to 10 mV. The capacity is dependent on the discharge cutoff voltage and cycling rate with some dependence on electrolyte composition. The first few cycles are dominated by the formation of the SEI followed by a fade to a steady, reversible capacity thereafter. Neglecting the capacity of the carbon additive can lead to significant errors in the estimation of charge storage capabilities of the active material.

Influence of Binders, Carbons, and Solvents on the Stability of Phosphorus Anodes for Li-ion Batteries.

Phosphorus (P) is an abundant element that exhibits one of the highest gravimetric and volumetric capacities for Li storage, making it a potentially attractive anode material for high capacity Li-ion batteries. However, while phosphorus carbon composite anodes have been previously explored, the influence of the inactive materials on electrode cycle performance is still poorly understood. Here, we report and explain the significant impacts of polymer binder chemistry, carbon conductive additives, and an under-layer between the Al current collector and ball milled P electrodes on cell stability. We focused our study on the commonly used polyvinylidene fluoride (PVDF) and poly(acrylic acid) (PAA) binders as well as exfoliated graphite (ExG) and carbon nanotube (CNT) additives. The mechanical properties of the binders were found to change drastically because of interactions with both the slurry and electrolyte solvents, significantly effecting the electrochemical cycle stability of the electrodes. Binder adhesion was also found to be critical in achieving stable electrochemical cycling. The best anodes demonstrated ∼1400 mAh/g-P gravimetric capacity after 200 cycles at C/2 rates in Li half cells.

Electrochemical Thin Layers in Nanostructures for Energy Storage.

Conventional electrical energy storage (EES) electrodes, such as rechargeable batteries, are mostly based on composites of monolithic micrometer sized particles bound together with polymeric and conductive carbon additives and binders. The kinetic limitations of these monolithic chunks of material are inherently linked to their electrical properties, the kinetics of ion insertion through their interface and ion migration in and through the composite phase. Redox chemistry of nanostructured materials in EES systems offer vast gains in power and energy. Furthermore, due to their thin nature, ion and electron transport is dramatically increased, especially when thin heterogeneous conducting layers are employed synergistically. However, since the stability of the electrode material is dictated by the nature of the electrochemical reaction and the accompanying volumetric and interfacial changes from the perspective of overall system lifetime, research with nanostructured materials has shown often indefinite conclusions: in some cases, an increase in unwanted side-reactions due to the high surface area (bad). In other cases, results have shown significantly better handling of mechanical stress that results from lithiation/delithiation (good). Despite these mixed results, scientifically informed design of thin electrode materials, with carefully chosen architectures, is considered a promising route to address many limitations witnessed in EES systems by reducing and protecting electrodes from parasitic reactions, accommodating mechanical stress due to volumetric changes from electrochemical reactions, and optimizing charge carrier mobilities from both the "ionic" and "electronic" points of view. Furthermore, precise nanoscale control over the electrode structure can enable accurate measurement through advanced spectroscopy and microscopy techniques. This Account summarizes recent findings related to thin electrode materials synthesized by atomic layer deposition (ALD) and electrochemical deposition (ECD), including nanowires, nanotubes, and thin films. Throughout the Account, we will show how these techniques enabled us to synthesize electrodes of interest with precise control over the structure and composition of the material. We will illustrate and discuss how the electrochemical response of thin electrodes made by these techniques can facilitate new mechanisms for ion storage, mediate the interfacial electrochemical response of the electrode, and address issues related to electrode degradation over time. The effects of nanosizing materials and their electrochemical response will be mechanistically reviewed through two categories of ion storage: (1) pseudocapacitance and (2) ion insertion. Additionally, we will show how electrochemical processes that are more complicated because of accompanying volumetric changes and electrode degradation pathways can be mediated and controlled by application of thin functional materials on the electrochemically active interface; examples include conversion electrodes, reactive lithium metal anodes, and complex reactions in a Li/O2 cathode system. The goal of this Account is to illustrate how careful design of thin materials either as active electrodes or as mediating layers can facilitate desirable interfacial electrochemical activity and resolve or shed light on mechanistic limitations of electrochemical processes related to micrometer size particles currently used in energy storage electrodes.

Electrochemical Accesebility of Platinum Nanoparticles Supported on Anatase TiO2 Using Conductive Carbon Additives

Degradation of carbon supports at the cathode of polymer electrolyte fuel cells is a critical issue leading to a decrease in activity of the platinum electrocatalysts. Metal oxides based on Ti and Sn have been studied as alternative supports, as they show high stability under severe cathodic conditions.1 However, these metal oxides are typically poorly conductive when compared with carbon support and needs to be either reduced or doped with other metals in order to be able to function as a conducting support. Making an electronically conductive path among nanosized metal oxides with conducting carbon-based materials may offer an alternative approach towards utilization of such non-conducting supports. In this study, we pursued the possibility of utilizing carbon nanotubes (CNTs) as a conducting additive to Pt nanoparticles deposited on non-conducing anatase-type TiO2. Pt nanoparticles were photo-deposited on anatase-type TiO2 (P25, average particle diameter=25 nm). The amount of platinum on TiO2 was adjusted to be 2 mass%. CNTs were added to a dispersion of Pt/TiO2, adjusted to 20 mass% CNT with respect to Pt/TiO2, and dried to prepare the CNT-Pt/TiO2 composites. The catalyst ink was dropped on a glassy carbon disk electrode (φ= 6 mm, 3.5 µg-Pt cm–2) and dried at room temperature. This electrode was used as the working electrode, and electrochemical studies were conducted with a three-electrode electrochemical cell setup. CO stripping voltammetry in 0.1 M HClO4electrolyte (25°C) was performed in order to estimate the electrochemically active surface area (ECSA) of the platinum nanoparticles. Figure (a) shows a typical transmission electron microscope (TEM) image of CNT-Pt/TiO2. CNTs form a network-like morphology with Pt/TiO2 particles. The average diameter of platinum nanoparticles determined from 150 particles was 2.9 nm. The specific surface area of the platinum nanoparticles based on the particle size was estimated to be 96 m2 g–1. ECSA was estimated from the oxidation charge of pre-adsorbed CO on platinum surface. The ECSA of CNT-Pt/TiO2 was 63 m2 (g-Pt)–1. Thus, the utilization of the platinum surface was 66% compared with the expected value, i.e. 96 m2 g–1. Although the ECSA of CNT-Pt/TiO2 was lower than Pt/C (83 m2 (g-Pt)–1, platinum particle size of 2.1 nm), the utilization of platinum surface was comparable with that of commercial Pt/C (62%). From these result, it is concluded that an electronically conductive path among platinum supported on TiO2particles was successfully established using a CNT network. 1) K. Sasaki, F. Takasaki, Z. Noda, S. Hayashi, Y. Shiratori, and K. Ito, ECS Trans., 33, 473 (2010). Figure 1

A Cost Efficient Silicon-Carbon Based Anode Material for Lithium-Ion Batteries

Silicon anodes have been proposed as anodes for Li-ion batteries due to their very high theoretical capacity. It has the potential to store ten times more lithium than graphite, the material commonly used in lithium-ion anodes [1]. However, great performance in one parameter comes with great costs in other parameters. Due to the extreme volume changes involved during lithiation and delithiation of silicon, cyclability becomes a challenge. The silicon-based anodes typically encounter massive cracking and degradation during electrochemical cycling, accompanied with a steady growth of SEI and reduction in conductivities, blocking of channels for electrolyte transport and irreversible consumption of Li-ions and electrolyte solvents. Typical mitigation methods involves using nanostructured silicon [2], building of hierarchical structured silicon composites [3], optimisation of binders [4] and adding appropriate SEI forming additives [5]. Silicon as anode material has now grown to a mature field, and many degradation phenomena has been explored in detail, in particular on nanostructured silicon using powerful in-situ TEM studies [6]. Some of the degradation mechanisms are well documented in the literature, while others are not so well understood. In this presentation we show indications of migration of silicon, electrochemical sintering, and the formation of a dendritic network on the surface of the silicon after long cycling of commercially relevant anodes, using post mortem FIB-SEM and TEM. We also show how these effects are mitigated by methods known to increase anode life-time, achieving >1200 cycles of 600 mAh/g total anode. The composite silicon-carbon anodes are based on industrial battery grade silicon produced at Elkem, one of the world’s leading companies for environment-friendly production of metals and materials. The anodes typically consist of nano-sized silicon crystallites induced by a milling pre-treatment, embedded in graphite and conductive carbon additives. The electrochemical performance was tested in half cells where typically the working electrode was made by mixing a silicon-carbon composite powder with an organic binder in an aqueous slurry and coated on a Cu-foil. Lithium metal was used as the counter electrode. Structural properties and degradation mechanisms were examined by electron microscopy (SEM, FIB-SEM, TEM) and XRD. The next stage in the development of the silicon-carbon based anode is to prepare full cells with a commercial cathode and industry-relevant loading on the anode. Work on Si/C full cells will be presented at the conference which will provide useful information about degradation mechanisms of silicon in a full cell, and tests its relevance as a commercial anode material. [1] D. Larcher, S. Beattie, M. Morcrette, K. Edström, J.-C. Jumas, and J.-M. Tarascon, J. Mater. Chem., vol. 17, no. 36, p. 3759, 2007. [2] U. Kasavajjula, C. Wang and A. J. Appleby, J. Power Sources, 2007,163, 1003; X. Su et al., Adv. Energy Mater., 4 (2014), p. 1300882. [3] Liu, N., Z.D. Lu, J. Zhao, M.T. McDowell, H.W. Lee, W.T. Zhao, and Y. Cui, Nature Nanotechnology, 2014. 9(3): p. 187-192. [4] D. Mazouzi et al. Journal of Power Sources, 280 (2015), pp. 533-549. [5] L. Chen, K. Wang, X. Xie, J. Xie . Journal of Power Sources, 174 (2007), pp. 538–543. [6] M.T. McDowell et al., Adv. Mater. 2013, 25, 4966 Figure 1

Electrochemical Performance and Structural Analyses of Amorphous TiS3 Positive Electrode in All-Solid-State Batteries

Development of all-solid-state rechargeable lithium batteries attracts much attention because of their high safety, long cycle life, versatile geometry and high energy density. To increase energy density of the batteries, the use of active materials with high capacity and the increase of active material content are important. Sulfur-rich amorphous transition metal sulfides such as TiS3 are promising positive electrodes with high capacity and high conductivity [1]. Amorphous TiS3 (a-TiS3) was prepared by mechanical milling of crystalline TiS3 (c-TiS3), which was prepared via solid-phase reaction in advance. The 80Li2S·20P2S5 (mol%) glass-ceramics and Li-In alloy were respectively used as a solid electrolyte and a negative electrode. A composite positive electrode was prepared by mixing of a-TiS3, the electrolyte, and acetylene black with the weight ratio of 40:60:6. All-solid-state cells with the composite positive electrode exhibited a high capacity of about 560 mAh per gram of a-TiS3 at 25oC and retained better cyclability than the cell with c-TiS3 [2]. XRD patterns and the Raman spectra of the a-TiS3 electrode after the 1st and 10th charge–discharge measurements were similar to those before the measurement [2,3]. In addition, the high resolution-TEM images after the 10th charge-discharge tests showed no periodic lattice fringes, indicating that the a-TiS3 electrode after 10 cycles did not have fine crystals with nanometer size. The most part of a-TiS3 electrode after charge-discharge measurements maintained amorphous structure. Furthermore, the cell with a-TiS3 positive electrode including no carbon conductive additives and solid electrolytes operated as a rechargeable battery and exhibited a reversible capacity for 10 cycles of about 510 mAh per gram of a-TiS3 [4]; the maximum content of active material in a positive electrode layer was achieved because of high conductivity of a-TiS3. The electronic structures of sulfur in a-TiS3 before and after charge-discharge tests were analyzed by X-ray photoelectron spectroscopy (XPS) with a monochromatic AlKa source (1486.6 eV). The samples were mounted on a sample stage in a dry Ar glove box and they were transferred to an analysis chamber using an Ar filled transfer vessel without exposure to air atmosphere. S2p XPS revealed that a reversible sulfur redox in a-TiS3 mainly appeared during charge-discharge process and contributed to its good capacity retention. It is noteworthy that amophization of TiS3 active material is effective in developing all-solid-state lithium batteries with higher reversible capacity and better cyclability. AcknowledgementThe research was financially supported by the Japan Science and Technology Agency (JST), Advanced Low Carbon Technology Research and Development Program (ALCA), Specially Promoted Research for Innovation Next Generation Batteries (SPRING) Project, and by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan.

No Significant Effect of Phosphorous Doping on the Electrochemical Performance of Silicon-Carbon Composite Anodes for Li-ion Batteries

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.

High Capacity Li2FeSiO4/Carbon Composite Cathode Powder Prepared By Spray-Frozen/Freeze-Drying Method

Much attention has been payed to lithium metal silicate (Li2MSiO4, M=Fe and Mn) as a promising cathode of large-scale lithium ion battery which can be used in electric vehicles and renewable energy generation systems. The Li2MSiO4, however, has a disadvantage in electronic conduction: their electrical conductivities are below 10-14 S/cm, which are much lower than those of LiCoO2. In addition, the diffusivity of lithium ion in the Li2MSiO4 is low compared with that in LiCoO2. Two approaches have been proposed for improvement in the conduction properties of Li2MSiO4: one is addition of conductive carbon, and the other reduction of particle size. Although various processes including use of expensive graphene and carbon nano-tube have been reported to obtain high capacity Li2MSiO4/carbon composite fine powders, it is important to develop cost-effective processes for broad commercial applications of the lithium ion batteries. The authors have applied spray-frozen/freeze-drying (SF/FD) process to preparation of Li2MSiO4/carbon composite fine powders. The SF/FD is a practical process based on combination of spray-drying and freeze-drying processes, leading to ceramic fine powders with large specific surface area in high purity. In this study, Li2FeSiO4/carbon composite powder was prepared by SF/FD of solutions containing carbon sources followed by heat-treatment in flowing argon. Indian ink and glucose was added as the carbon sources. High capacity of 255 mAh/g was obtained at an initial discharge for the as-prepared Li2FeSiO4/carbon composite cathode powders even though any conductive additives were not added to the composite powders thus prepared. The Li2FeSiO4 showed high value of 173 mAh/g even after ten cycles of charge/discharge. This result indicates that most of Li2FeSiO4 particles are connected with carbon network from the starting carbon sources. The capacity at an initial discharge was increased to 323 mAh/g by adding an amount of Ketjenblack to the composite powder. The value became 238 mAh/g after ten cycles. TEM observations revealed that most of Li2FeSiO4 particles had size of 30-50 nm and the nano-Li2FeSiO4 particles were homogeneously complexed with colloidal carbons from Indian ink. In addition, it was observed that the nano-Li2FeSiO4 particles were coated with carbon layer with about 2 nm in thickness. Thus, homogeneous composites of Li2FeSiO4 and carbon nano-particles were successfully prepared by SF/FD of the solutions containing two kinds of carbon sources, leading to high cathode performance. These results clearly indicate that the practical SF/FD process can be applied for preparation of high capacity Li2FeSiO4/carbon composite cathode powder.

Novel Binary Binder PAA-SBR Towards Silicon Anodes in Li-Ion Batteries

Silicon remains a promising anode material for next generation lithium-ion batteries, despite the well-documented issues associated with it, due to its abundance and high capacity (3579mAh/g: almost 10 times higher than the capacity of graphite). The problems still facing Si-based battery commercialization are volume expansion, which results in rapid capacity fade, and continued Li loss through SEI formation from electrolyte decomposition. To address this problem, effective binders are considered to be one solution, and could help to maintain good contact between the active material and current collector but also to generate effective, stable networks between silicon particles and conductive carbon additives. This work will introduce a new binder system: Polyacrylic Acid-Styrene Butadiene Rubber (PAA-SBR). PAA is an aqueous-based polymer and possesses a high concentration of carboxyl group, which effectively bonds with the surface of silicon but also can H-bond with other polar species contributing to a good cohesive composite. SBR (Styrene Butadiene Rubber) is well known for its good flexibility, which can improve the tensile property of the electrode towards volume expansion. Therefore, it is hypothesized that the binary binder PAA-SBR can help Si anode achieve an improved, more stable performance because it can preserve good adhesion and flexibility simultaneously under the stress of the Si expansion. A preliminary study was conducted on Si vs.Li/Li+ half cells with different binder systems: PAA, PAA-SBR (2:1 mass ratio) and PAA-SBR (5:1 mass ratio), where PAA-only is used as the control binder. Cells are tested under the maximum lithiation capacity of 1200mAh/g at a C rate of C/5. Electrochemical cycling data indicates that for first 100 charge-discharge cycles, the PAA-SBR (2:1) showed a similar level of performance compared with PAA in terms of specific capacity (~1194mAh/g) and columbic efficiency (~99.5%), while the PAA-SBR (5:1) displayed capacity fade after 80 cycles, as shown in Fig.1. We anticipate that an optimized PAA-SBR ratio will generate superior composite durability during longer-term electrochemical testing. To further approve the hypothesis, a comprehensive study based on PAA-SBR (2:1) will be followed including polymer stability in electrolyte solvents, tensile properties, adhesion and impedance testing. Figure 1

Degradation Phenomena in Silicon-Carbon Composite Anodes from Industrial Battery Grade Silicon

Silicon is a remarkable material - even in lithium ion battery technology it seems to find its utilisation. Silicon has the potential for storing ten times more lithium than graphite, the material commonly used in lithium ion anodes [1]. But, as always, great performance in one parameter comes with great costs in other parameters. Due to the extreme volume changes involved during lithiation and delithiation of silicon, cyclability becomes a huge challenge. The silicon-based anodes typically encounter massive cracking and degradation during electrochemical cycling, accompanied with a steady growth of SEI and reduction in conductivities, blocking of channels for electrolyte transport and irreversible consumption of Li-ions and electrolyte solvents. Typical mitigation methods involves using nanostructured silicon [2], building of hierarchical structured silicon composites [3], optimisation of binders [4] and adding appropriate SEI forming additives [5]. Silicon as anode material has now grown to a mature field, and many degradation phenomena has been explored in detail, in particular on nanostructured silicon using powerful in-situ TEM studies [6]. The full theoretical capacity of silicon is not required for lithium ion batteries in the near term future since the cathode materials available today becomes too limiting for the overall capacity. Thus, composite anodes containing silicon and a conventional anode material such as graphite will likely be sufficient to meet the short-term targets for anode materials. However, degradation phenomena specific to composite silicon-carbon electrodes has not been studied in same detail as for pure nano-silicon structures. In addition, in situ TEM often suffer from the fact that only a single cycle, or a limited amount of cycles, has been observed. In our work we have performed post-mortem FIB-SEM and TEM studies to investigate degradation occurring over multiple cycles examining the effect and interplay between the graphite and the silicon in composite anodes and in this presentation we will explore different degradation phenomena observed in silicon-carbon composite anodes including: Electrode thickeningSilicon migrationElectrochemical sinteringDendritic surface formationInhomogeneous lithiationStrong dependence on lithiation level and electrode thickness The composite silicon-carbon anodes are based on industrial battery grade silicon produced at Elkem, one of the world’s leading companies for environment-friendly production of metals and materials. The anodes typically consist of nano-sized silicon crystallites induced by a milling pre-treatment, embedded in graphite and conductive carbon additives. The electrochemical performance was tested in half cells where typically the working electrode was made by mixing a silicon-carbon composite powder with an organic binder in an aqueous slurry and coated on a Cu-foil. Lithium metal was used as the counter electrode. Structural properties and degradation mechanisms were examined by electron microscopy (SEM, FIB-SEM, TEM) and XRD.