Lithium-ion Cathode Research Articles

Unraveling the effects on lithium-ion cathode performance by cation doping M-Li2CuO2 solid solution samples (M = Mn, Fe and Ni).

Cation doping is one of the most dynamic strategies to enhance the electrochemical properties of cathode materials for lithium-ion batteries. Nevertheless, the maximum partial substitution capacity depends on the solubility of each metal ion, and so the formation of impurities is a very common consequence. Thus, the correlation between electrochemical performance and the doping effect is frequently unknown. In this study, the effect of the partial substitution of copper by manganese, iron or nickel in Li2CuO2 is evaluated, as well as the effect on the electrochemical performance of the modified Li2CuO2 samples as lithium ion battery cathode materials. XRD characterization confirmed single phase formation for all samples, and the incorporation of the transition metal in the Li2CuO2 structure was evaluated by XRD profile fitting, EPR and 7Li-NMR. The results showed modifications in intra- and inter-chain interactions, associated with the variations in the Cu-O-Cu bond angle and changes in magnetic order, due to the presence of the doping transition metal. Among all samples, only manganese partial substitution reveals a drastic improvement in the electrochemical stability during the charge/discharge processes even at potentials higher than 3.9 V. It was corroborated that the higher stability is attributed to (i) the increase in the superexchange interactions between the copper sites and manganese, directly modifying lithium diffusivity and electronic conductivity, both inferred from dynamic thermogravimetric analysis for CO2 sorption and conductivity tests, respectively and (ii) the lower propensity to enable O2 evolution during several charge cycles. These results are totally attributed to manganese cation partial substitution, which has a huge impact on the utilization of copper-based materials in real applications.

Stable surface construction of the Ni-rich LiNi0.8Mn0.1Co0.1O2 cathode material for high performance lithium-ion batteries

LixNi1−yFeyO2&NiFe2O4in situ surface modified NCM cathode materials have been successfully fabricated and utilized as high performance lithium-ion cathode materials.

Unveiling and Amplifying the Benefits of Carbon-Coated Aluminum Current Collectors for Sustainable LiNi0.5Mn1.5O4 Cathodes

Implementing aqueous electrode processing for lithium-ion cathodes is one of the key steps toward the achievement of environmentally benign battery production and of utmost importance in light of t...

Origin of Enhanced Cyclability in Covalently Modified LiMn1.5Ni0.5O4 Cathodes.

High-voltage lithium-ion cathode materials exhibit exceptional energy densities; however, rapid capacity fade during cell cycling prohibits their widespread utilization. Surface modification of cathode-active materials by organic self-assembled monolayers (SAMs) has emerged as an approach to improve the longevity of high-voltage electrodes; however, the surface chemistry at the electrode/electrolyte interphase and its dependence on monolayer structure remains unclear. Herein, we investigate the interplay between monolayer structure, electrochemical performance, and surface chemistry of high-voltage LiMn1.5Ni0.5O4 (LMNO) electrodes by the application of silane-based SAMs of variable length and chemical composition. We demonstrate that the application of both hydrophobic and hydrophilic monolayers results in improved galvanostatic capacity retention relative to unmodified LMNO. The extent of this improvement is tied to the structure of the monolayer with fluorinated alkyl-silanes exhibiting the greatest overall capacity retention, above 96% after 100 charge/discharge cycles. Postmortem surface analysis reveals that the presence of the monolayer enhances the deposition of LiF at the electrode surface during cell cycling and that the total surface concentration correlates with the overall improvements in capacity retention. We propose that the enhanced deposition of highly insulating LiF increases the anodic stability of the interphase, contributing to the improved galvanostatic performance of modified electrodes. Moreover, this work demonstrates that the modification of the electrode surface by the selection of an appropriate monolayer is an effective approach to tune the properties and behavior of the electrode/electrolyte interphase formed during battery operation.

A path toward cobalt-free lithium-ion cathodes

The necessity of developing low-cobalt cathode oxides for lithium-ion batteries is increasingly apparent. The most popular strategy followed thus far in addressing this issue has been the development of LiNiO2-like, Ni-rich, layered LiMO2 (M = Ni, Mn, Co; NMC) oxides with low Mn and Co contents, e.g., NMC-811. However, safety, cycle-life, and even cost could remain critical barriers to the success of such cathode materials. Herein an alternative to LiNiO2-based, low-cobalt cathodes is suggested based on modifications to the prototypical cobalt-free, layered oxide, LiNi0.5Mn0.5O2.

(Invited) Thiophosphate Based Solid Electrolytes and Cathodes Interfaces

Stable high ion-conducting solid electrolytes are enablers for all solid state batteries. Among many class of materials, Lithium thiophosphate family of solid electrolytes have been investigated for their (a) superionic ion-conductivity (>10-4 S/cm), (b) mechanical softness and higher interfacial wettablity, (c) relatively simple synthesis and processing routes and (d) lower cost and earth abundance. Despite such advantages thiophosphates are known to have a narrow electrochemical stability window with a thermodynamical stability window between 1.7-2.6V (with respect to Li+/Li). Under such scenario, interfacial stability between Lithium thiophosphate/Li-metal and cathodes are primarily dictated by kinetic control by formation of a reaction passivation layer. Interfacial charge transfer depends on the detailed composition of the passivation reaction at the interface. The talk will highlight on the electrochemical performance characterization of the solid electrolyte, Li3PS4 and lithium-ion cathode such as LiFePO4. Detailed interfacial characterization between Li3PS4 and cathode interphases probed by XPS, NMR and electrochemical impedance spectroscopy (EIS) will be presented. In addition, synthesis and characterization of high capacity polysulfidophosphate cathodes based on catenation of sulfur to thiophosphate electrolytes, Li3(PS4)Sn where n = 5,8,6,3,2 will be discussed.

(Invited) Towards the Realization of Sustainable High-Performance Lithium-Ion Batteries: Aqueous Processing of Cobalt-Free High-Energy Cathodes

The recently rising awareness for a more sustainable cell manufacturing can be expected to gain even more momentum in sight of the announcements from major car manufacturers across Europe and North America to entirely electrify their fleet within the next half-decade1,2. The implementation of aqueous electrode processing strategies for lithium-ion cathodes is a key step to realize the environmentally benign battery production. To achieve this ambitious goal, most studies focus on the development of non-toxic and abundant active materials and specifically, the implementation of nature-derived, inexpensive binders in combination with the use of water as dispersion agent and solvent provides the great possibility to spare energy-intensive drying procedures and costly dry-room conditions, and thus, will turn the whole battery fabrication more eco-efficient 3,4. What could easily be established for graphite anodes – employing water-soluble natural polymers as binder, thus, abolishing the need of toxic and rather costly N-methyl-2-pyrrolidone (NMP) as processing solvent3,5 – appears more complicated for transition metal oxide-based and imperatively cobalt-free cathode materials, which suffer from lithium leaching and transition metal dissolution when getting in contact with water, which has, so far, rendered the use of aqueous binders very challenging6,7. In our group we recently demonstrated the general feasibility for the aqueous processing of several lithium-ion cathode materials, such as high-voltage LiNi0.5Mn1.5O4, by introducing a complementary approach, of suitable processing additives to stabilize the active material surface as well as the electrode/electrolyte/current collector interface8. Moreover, we extended our investigations to various binder systems and cathode materials in order to advance the aqueous electrode preparation and move from the well-established lab-scale process towards the fabrication of commercial-scale lithium-ion batteries9. References C. J. Barnhart and S. M. Benson, Energy Environ. Sci., 6, 1083 (2013).D. Larcher and J. M. Tarascon, Nat. Chem., 7, 19–29 (2015).D. Bresser, D. Buchholz, A. Moretti, A. Varzi, and S. Passerini, Energy Environ. Sci. (2018) http://xlink.rsc.org/?DOI=C8EE00640G.A. Kwade et al., Nat. Energy, 3, 290–300 (2018) http://www.nature.com/articles/s41560-018-0130-3.S. F. Lux, F. Schappacher, A. Balducci, S. Passerini, and M. Winter, J. Electrochem. Soc., 157, A320 (2010).M. M. Thackeray, J. Am. Ceram. Soc., 82, 3347–3354 (1999).N. Loeffler et al., ChemSusChem, 9, 1112–1117 (2016).M. Kuenzel et al., ChemSusChem, 11, 562–573 (2018).A. Kazzazi et al., ACS Appl. Mater. Interfaces, 10, 17214–17222 (2018).

Effects of lithium excess and Ni content on the electrochemical performance of Li1+x (Ni0.45−xMn0.4Co0.15) O2 lithium-ion cathode materials in stoichiometric state

In Li-ion batteries, application of active materials can enhance the kinetics of the charge-discharge process, reduce the costs and improve the safety of the system. In this work, the effect of nickel content and lithium excess in Li1+x (Ni0.4−xMn0.5Co0.1) O2 compounds on the electrochemical performance of the lithium-ion battery cathode have been studies. For this purpose, three compounds of NMC in the stoichiometric state were synthesized via co-precipitation as the cathode active material. XRF and EDS analyses indicate that precursors and oxide compounds are well synthesized. The final compound of synthesized cathodes was obtained by ICP analysis. XRD results also suggest that the hydroxide and oxide phases are formed appropriately. SEM results show that the particle size of the synthesized samples ranges from 1–2 μm. As the content of nickel increases (sample 3), particle sizes also increase. The battery charge-discharge test results (at rates of 0.1–5 C) show that when the nickel content is 0.45, the cycle life of the sample 3 is lower than the other two (154 mAh g−1 at discharge rate 1 C). While the discharge capacity for the sample 1 at 1 C and 5 C rates after 30 cycles is 176.9 mAh g−1 and 101.4 mAh g−1, respectively. Therefore, as a result, to increase the cathode capacity, the amount of lithium can be increased as well as the amount of nickel can be reduced in a stoichiometric state.

Quantifying Transport, Geometrical, and Morphological Parameters in Li-Ion Cathode Phases Using X-ray Microtomography.

The charge/discharge capabilities of Li-ion cathodes are influenced by the meso-scale geometry, transport properties, and morphological parameters of the constituent phases in the cathode: active material, binder, conductive additive, and pore. Electrode processing influences the structure and attendant properties of these constituents. Thus, performance of the battery can be enhanced by correlating various electrode processing techniques with the charge/discharge behavior in the lithium-ion cathodes. X-ray microtomography was used to image samples obtained from pristine Li(Ni1/3Mn1/3Co1/3)O2 (NMC) cathodes subjected to distinct processing approaches. Two sample preparation approaches were applied to the samples prior to microtomography. Casting the samples in epoxy yielded only the cathode active material domain. Encapsulating the sample with Kapton tape yielded phase contrast data that permitted segmentation of the active material and combined carbon/binder and pore regions. Geometrical and morphological details of the active material and the secondary phases were characterized and compared between the varied processing approaches. Calendered and ball-milled samples exhibited distinct differences in both geometry and morphology. Drying modes demonstrated variation in the distribution of the secondary and pore phases. Applying phase contrast capabilities, the processing-morphology relationship can be better understood to enhance overall battery performance across multiple scales.

(Invited) The Scalability of Accelerating Rate Calorimetry (ARC) with State of Charge and Capacity

Sandia National Laboratories has used Accelerating Rate Calorimetry (ARC) as a means to evaluate and compare the total energies of thermal runaway. This has been an invaluable tool for evaluating the behavior of new chemistries as they become available in commercial and prototype cells. However, this testing has typically been performed in 18650 cells of ~1-1.5 AH and on cells at 100% state of charge. This has been invaluable for the evaluation and comparison of the thermal runaway of different lithium ion battery chemistries, however it leaves open questions as how changes to energy density, cell size and state of charge impact the results from calorimetry testing. This work examines the results of accelerating rate calorimetry testing on different lithium ion cathode chemistries (LCO, NCA, NMC, LFP) different formats (18650, pouch, large format cylindrical) and states of charge to understand how ARC results are impacted by both energy density and total energy. Also studied are how thermal runaway is impacted by energy in general, looking at both the total energy release during thermal runaway as well as the peak heating rates observed. While the total energy release is expected to correlate with the stored energy of the cell, the peak heating rates will impact how cells might behave in a variety of conditions. This has implications for battery design, as data suggests that even cells at relatively low states of charge may be hazardous if sufficiently insulation allows self-heating to occur even at relatively low rates; figure 1 shows data collected on 14 AH pouch cells summarizing the observed runaway energies and peak heating rates. This shows a relatively linear response as the stored energy increases, however an exponential response is observed with respect to state of charge. While this affirms the conventional wisdom that low state of charge cells are unlikely to go into thermal runaway in most environments, we can still see significant stored energy even at relatively low states of charge. The right conditions may still make these cells hazardous, making it important to fully understand the thermal decomposition of cells under a wide variety of conditions. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. Figure 1 Comparison of total enthalpy observed during runaway of a 14 AH pouch cell to the peak heating rates at various states of charge. Figure 1

Hidden structural and chemical order controls lithium transport in cation-disordered oxides for rechargeable batteries

Structure plays a vital role in determining materials properties. In lithium ion cathode materials, the crystal structure defines the dimensionality and connectivity of interstitial sites, thus determining lithium ion diffusion kinetics. In most conventional cathode materials that are well-ordered, the average structure as seen in diffraction dictates the lithium ion diffusion pathways. Here, we show that this is not the case in a class of recently discovered high-capacity lithium-excess rocksalts. An average structure picture is no longer satisfactory to understand the performance of such disordered materials. Cation short-range order, hidden in diffraction, is not only ubiquitous in these long-range disordered materials, but fully controls the local and macroscopic environments for lithium ion transport. Our discovery identifies a crucial property that has previously been overlooked and provides guidelines for designing and engineering cation-disordered cathode materials.

Hidden Structural Order Controls Li-Ion Transport in Cation-Disordered Oxides

The development of cost-effective lithium-ion batteries depends on the discovery of high-energy-density cathode materials composed of nonprecious elements. Traditionally, lithium-ion cathodes are based on two categories, i.e., layered oxides and polyanionic compounds. However, most polyanionic compounds have low specific capacity due to their heavy polyanions. Layered oxides, though more favorable for energy density purposes, often contains the element cobalt, the supply of which is scarce and not sustainable. The discovery of cation-disordered rocksalts and their percolation rules unlocked an unprecedented chemical space for the exploration of high-capacity lithium-ion cathodes which do not contain Co and have high capacity[1]. The facile Li diffusion in these materials is enabled through a network of Li-rich environments (so-called 0-TM channels) created by excess Li. Following this insight, many new high-energy-density cathode materials that involve mostly earth-abundant elements have been developed, such as Li1.2Mn0.4Ti0.4O2[2], Li1.2Ni1/3Ti1/3Mo2/15O2[3], as well as their fluorinated variants[4, 5]. A prevailing assumption when studying disordered rocksalt cathodes is that all the cation species are randomly distributed. However, we will demonstrate that even minor deviations from randomness, not detectable by typical X-ray diffraction (XRD), can have profound influence on performance. We employ a combination of thorough experimental characterization and multi-scale computer simulations to reveal that cation short-range order is ubiquitous in these long-range disordered materials. More importantly, the short-range order controls Li transport by altering the distribution of local environments and the connectivity between them. By considering a variety of different chemistries, we explain the microscopic origin of short-range order and identify general guidelines for local-structure manipulation for the benefit of Li transport. This breakthrough in the fundamental understanding of structure-property relationship in disordered Li-ion cathodes sets an exciting new direction for future optimization. [1] J. Lee, et al, Science 343 (2014) 519-522. [2] N. Yabuuchi, et al, Nature communications 7 (2016) 13814. [3] J. Lee, et al, Energy & Environmental Science 8 (2015) 3255-3265. [4] R. Chen, et al, Advanced Energy Materials 5 (2015). [5] J. Lee, et al, Nature communications 8 (2017) 981.

(Plenary) NMR and PDF Studies of Local Structure and Dynamics: Applications to Lithium and Sodium Ion Batteries

This talk will focus on method developments to understand structure and dynamics in Li, Na and Mg batteries using a series of local structural probes. Recent studies to improve our understanding of hard carbons for Na-ion batteries will be discussed using both NMR and pair distribution function (PDF) analysis. Here we use both methods to correlate structure with the capacity observed in both the sloping and flat, low voltage component of the electrochemical curve. NMR studies to study dynamics in lithium-ion cathode and anode materials will be discussed. For example, a series of high rate Nb-oxide electrodes and the structures that allow high Li transport and extremely high rates even when micrometer-sized will be described. These structures adopt crystallographic shear and bronze-like structures, and retain open diffusional channels for Li over a wide range of lithium compositions. In part, this is due to structural motifs present in, for example, the shear structures that prevent rotation of the perovskite corner edge sharing octahedra that clamp the Li in place in ReO3-type structures. Their lithium-ion diffusion coefficients (D Li) were measured with pulsed field gradient NMR spectroscopy and have room temperature values that are several orders-of-magnitude faster than typical electrode materials.

Spectroscopic characterization of LiFePO4 as cathode material for Li-ion battery prepared in the pulse thermo-acoustic reactor

Lithium iron phosphate (LiFePO4) is a cathode material for the rechargeable-lithium batteries. In this paper is presented a novel method of fabrication carbon-coated LiFePO4 in a pilot reactor built according to the principles of the thermo-acoustic burner of Helmholtz-type. Crystalline powder with a high percentage of LiFePO4 was synthesized by incomplete combustion, i.e. in the reductive atmosphere, and calcined at 700?C for 6 h. The obtained samples were characterized by X-ray diffraction, IR and Raman spectroscopy. The aim of this study was to demonstrate the production of the high-quality lithium-ion cathode material by the incomplete combustion. The synthesis of LiFePO4 is completed during calcination and an ordered structure is attained. Fast synthesis in the reactor (less than 2 s) is achieved due to the reduction in the size of reactant's particles and a huge number of collisions owing to their strong turbulent flow associated with explosive combustion.

Effect of electrolyte composition on rock salt surface degradation in NMC cathodes during high-voltage potentiostatic holds

Surface degradation of lithium-ion cathodes at high voltages represents a significant barrier to increasing the useable energy of conventional cathodes. Though much work has been focused on mitigating the detrimental effects of such phenomena, the complex and correlated mechanisms involved have made progress difficult. Herein, the effect of electrolyte identity on surface degradation is examined. LiNi0.5Mn0.3Co0.2O2 (NMC532)/Li4Ti5O12 (LTO) full cells were constructed using three different electrolytes: a baseline organic carbonate electrolyte, a baseline organic carbonate electrolyte with an oxidizable additive, and a fluorinated carbonate electrolyte. Each system was subjected to a 60 h potentiostatic hold at 3.05 V (4.6 V vs. Li+/Li) and subsequently deconstructed for characterization via transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). Molecular simulations were carried out on each distinct component of the three electrolytes in contact with crystal surfaces of an NMC532 particle. Results indicate an affinity for the additive-containing electrolyte to extract atomic oxygen from the cathode surface, whereas the fluorinated electrolyte components have negligible interactions. Hydrogen abstraction from the baseline electrolyte is facilitated by the NMC532 surface. TEM analysis of cathode surfaces, after the potentiostatic holds, revealed that the NMC532 particles cycled with the additive-containing electrolyte underwent significant surface degradation, including changes to local crystal structure in a region penetrating 20–40 nm from the surface; consistent with oxygen and lithium loss from the cathode material. However, the NMC532 in contact with the fluorinated electrolyte showed a disordered layer of just a few nm in thickness, similar to the depth of crystal disorder observed in pristine NMC532 primary particles. EELS data of the oxygen K-edge also indicated transition metal (TM) reduction, consistent with oxygen loss and changes in crystal structure extending into the cathode surface for each of the electrolytes surveyed. These surface reactions, including oxygen loss, are shown to correlate well with elevated oxidation currents and surface reconstructions of cathode particles.

Short-Range Order and Unusual Modes of Nickel Redox in a Fluorine-Substituted Disordered Rocksalt Oxide Lithium-Ion Cathode

Fluorine substitution for oxygen in cation-disordered lithium-excess transition metal oxides (Li1+xTM1–xO2) used as lithium-ion cathodes was recently demonstrated to improve the reversibility of the processes taking place on charge and discharge by reducing the amount of oxygen loss on charge and preventing major structural rearrangements at high voltage. Yet, little is understood about how fluorine incorporates the oxide structure and impacts its electrochemical properties. Here, we use a combination of experimental (solid-state nuclear magnetic resonance (NMR) spectroscopy) and theoretical techniques (density functional theory (DFT) calculations and Monte Carlo simulations) to investigate the evolution of the local structure around fluorine and lithium and the oxidation state of redox-active nickel during charge and discharge of the Li1.15Ni0.45Ti0.3Mo0.1O1.85F0.15 (LNF15) cathode. We show that fluorine doping introduces short-range order in as-synthesized LNF15 by incorporating in lithium-rich sites wi...

Frontiers of Chemical Space

In a recent paper in Energy & Environmental Science, Gerbrand Ceder and colleagues outline a general strategy to design for high transition metal capacity in disordered rocksalt lithium ion cathodes, without reliance on cobalt. Guided by deep consideration of the fundamental limitations of well-studied cathode materials, as well as recent discoveries of Li-percolation in disordered rocksalts and fluorine substitution for oxygen, the authors propose, synthesize, and demonstrate a new high-energy-density cathode material based on both manganese (Mn2+/4+) and vanadium (V4+/5+) redox couples.

Towards the Realization of Aqueous Electrode Processing for Sustainable High-Energy Lithium-Ion Cathodes

The rapidly growing use of lithium-ion batteries in a multitude of applications, ranging from handheld portable devices over electric bikes and scooters to (hybrid) electric cars and stationary energy storage, has awakened an increasing awareness for a more sustainable cell manufacturing. In fact, improving the environmental benignity of lithium-ion batteries is of utmost importance for their large-scale employment.1,2 To achieve this goal, all stages of cell fabrication must be taken into consideration. This includes not only the incorporation of non-toxic and readily available active materials, but also the development of environmentally-friendly and cheap binding agents, which can ideally be processed in water, thus sparing energy-intensive drying procedures and dry-room conditions and, as a result, turning the whole battery fabrication more eco-efficient. For graphite anodes, for instance, the utilization of water-soluble cellulose-based binders did not only render the use of toxic N-methyl-2-pyrrolidone as solvent unnecessary, but moreover led to substantial improvement in terms of cycling stability and first cycle coulombic efficiency.3,4 For the cathode side, however, the pronounced sensitivity of lithium transition metal oxides (e.g., LiNi0.5Mn1.5O4 (LNMO), Li[Ni1/3Mn1/3Co1/3]O2 (NMC), or Li2MnO3*NMC) towards water in combination with the resulting severe pitting corrosion of the aluminum current collector has so far prevented the implementation of aqueous binders and processing techniques.5–7 In this regard, our recent results, following a complementary approach to enable the aqueous processing of high-voltage LNMO by introducing suitable processing additives in order to stabilize the active material/water as well as the electrode/electrolyte/current collector interface, demonstrate the great potential to realize more sustainable lithium-ion cathodes. The synergistic interaction of an in situ surface coating of the active material particles paired with the crosslinking of the cellulose-based binder yields water-processed electrodes without pitting corrosion, enhanced cycling stability, improved rate performance, and overall higher specific capacities.8 Herein, we will address the remaining challenges encountered after establishing the aqueous lab-scale processing of these high-voltage lithium-ion cathodes to eventually achieve commercially viable cathode tapes, readily available for large-scale, high-energy lithium-ion batteries. These addressed challenges include improvements concerning the electrode to current collector adhesion, the binder distribution and electrode components cohesion, as well as the realization of highly stable cycling without a steady initial capacity increase and coulombic efficiencies, exceeding those for LNMO-based electrodes comprising the state-of-the-art poly(vinylidene difluoride) (PVdF) binder. References D. Larcher and J. M. Tarascon, Nat. Chem., 7, 19–29 (2015).C. J. Barnhart and S. M. Benson, Energy Environ. Sci., 6, 1083 (2013).H. Buqa, M. Holzapfel, F. Krumeich, C. Veit, and P. Novák, J. Power Sources, 161, 617–622 (2006).S. F. Lux, F. Schappacher, A. Balducci, S. Passerini, and M. Winter, J. Electrochem. Soc., 157, A320 (2010).X. Zhang et al., J. Power Sources, 196, 5102–5108 (2011).M. M. Thackeray, J. Am. Ceram. Soc., 82, 3347–3354 (1999).N. Loeffler et al., ChemSusChem, 9, 1112–1117 (2016).M. Kuenzel et al., ChemSusChem, 11, 562–573 (2018).

Influence of the Structure of Parent Materials in Blended Li2CuO2-Limx Cathodes, Limx = LiFePO4, LiCoO2 and LiMn2O4

In recent years, it has been demonstrated that the use of blended cathodes is a convenient method for improving the performance of Lithium ion batteries by exploiting the advantageous properties of the parent materials. Blended cathodes allow the tailoring of cathodes with specific characteristics, often beyond the capabilities of any of the parent materials. While there are many high specific capacity lithium ion cathode materials, most of them lack long term stability for commercial use, for instance, Li2CuO2 is a promising material with a theoretical capacity of 490 mAh g-1; however, it exhibits a large capacity fade [1]. High capacities are only obtained during the first cycle, subsequent cycles presenting large capacity fade mainly due to structural transformations of the orthorhombic Li2CuO2 to densely packed layered structure during charging [1]. The present work aims to utilize commercial active materials to stabilize the Li2CuO2 phase and inhibit its degradation via blending. The materials chosen for this study are LiFePO4, LiCoO2 and LiMn2O4 considering their high stability, different structure and different average operation voltages (olivine/3.4 V, layered/3.8 V, spinel/4.1 V respectively) [2]. The blending process carried out in this study is via ball mill, because preliminary results have shown that physical mixing via stirring does not yield important synergic effects between the blended materials. Cycling Li2CuO2 at 0.1 C yields an initial capacity of 165 mAh g-1, with a capacity fade of 55 mAh g-1 after only ten cycles, while Li2CuO2/LiFePO4 cathode blends exhibit only a 22 mAh g-1 capacity fade, despite an initial capacity of 120 mAh g-1. Furthermore Li2CuO2/LiCoO2 cathode blends only present a capacity fade of 6 mAh g-1 after ten cycles, with an initial capacity of 112 mAh g-1. Lastly, preliminary results of the Li2CuO2/LiMn2O4 blends have also shown a slight improvement with respect to cyclability. It is evident that the different structure and average voltage of the secondary active material has a large impact on the capacity fade of the blended cathode, it is of great interest to identify the key parameters which optimize the performance of the blended cathode through further analysis by spectroscopic methods. The authors thank CONACyT project No. 1456 and SECITI project seciti/080/2017 for the financial support.

New Electrolyte Composition for High-Voltage Lithium-Ion Cathodes – Enhancing the Cycling Stability in Half- and Full-Cells

The steadily rising utilization of lithium-ion batteries for large-scale applications, in particular, electric vehicles requires the development of cell chemistries that offer increased energy and power densities.1,2 Essentially, there are two options to enhance the energy density: Increasing the capacity of the employed active materials and/or elevating the full-cell voltage by switching to high-voltage cathode materials. The latter, however, face the great challenge to identify a suitable electrolyte composition, as commonly used organic carbonate-based electrolyte are not sufficiently stable towards oxidation. To avoid the resulting detrimental side reactions, the use of electrolyte additives is easily implementable into common cell manufacturing technologies and, thus, very cost-efficient.3,4 For such reason, a plethora of electrolyte additives has been reported in recent years, but frequently these additives have been proven only to enhance the performance for selected cathode materials, while particularly the evaluation with graphite-based anodes has been commonly overlooked. Herein, we report on a new electrolyte composition, incorporating functional electrolyte additives for high-voltage cathode materials like LiNi0.5Mn1.5O4 or 5V-olivines, which moreover reveal a beneficial impact also for graphite-based anodes and, consequently, also in lithium-ion full-cells. As a result, lithium-ion half- and full-cells with a cell voltage of >4.5 V show a greatly enhanced cycling stability, increased capacities, and improved efficiencies. References B. Scrosati, J. Hassoun, and Y.-K. Sun, Energy Environ. Sci., 4, 3287 (2011).D. Bresser et al., J. Power Sources, accepted manuscript (2018).S. S. Zhang, J. Power Sources, 162, 1379–1394 (2006).J. Kalhoff, G. G. Eshetu, D. Bresser, and S. Passerini, ChemSusChem, 8, 2154–2175 (2015).