Li O2 Cathode Research Articles

H3PO4 treatment to enhance the electrochemical properties of Li(Ni1/3Mn1/3Co1/3)O2 and Li(Ni0.5Mn0.3Co0.2)O2 cathodes

In this study, Li(Ni1/3Mn1/3Co1/3)O2 (NMC333) and Li(Ni0.5Mn0.3Co0.2)O2 (NMC532) have been subjected to a phosphoric acid (H3PO4) solution treatment to form a thin Li3PO4 coating on their surfaces. The Li3PO4 coating formed is found to be very potent in enhancing the specific capacity of the first discharge as well as the rate capability and capacity retention in the subsequent charge/discharge cycles for both NMC333 and NMC532. The specific capacity of the first discharge for NMC532 has been increased drastically from ∼160 mA h g−1 for pristine NMC532 to ∼250 mA h g−1 for Li3PO4-coated counterpart at 0.1C and such a large capacity enhancement is retained throughout the subsequent cycles at 1C. The final specific capacity of Li3PO4-coated NMC532 is 187 mA h g−1 after 100 cycles at 1C, whereas the corresponding value of pristine NMC532 is only 50 mA h g−1. The rate capability has also been improved significantly with Li3PO4-coated NMC532 exhibiting ∼150 mA h g−1 capacity at 6C while pristine NMC532 showing zero capacity. Similar improvements have also been achieved with NMC333. These results demonstrate that the H3PO4 treatment is a facile and general method to improve the electrochemical properties of NMCs with different compositions and can be utilized for practical applications.

The Mechanism and Characterization of Accelerated Capacity Deterioration for Lithium-Ion Battery with Li(NiMnCo) O2 Cathode

Battery capacity plummeting severely threatens the endurance mileage and security of electric vehicles. A profound understanding of the mechanisms of accelerated capacity deterioration is a prerequisite for recognizing capacity plummeting online. In this paper, battery cycle life tests are performed under various cycle conditions until capacity plummeting. Based on the mathematical model of cathode and anode's open circuit voltage, an improved non-destructive diagnostic algorithm is proposed to quantify battery aging modes including loss of lithium inventory, loss of cathode active material and loss of anode active material. By analyzing the evolution characteristics of battery aging modes along with cycling, capacity plummeting mechanisms are concluded, including lithium plating on anode and collapse of cathode active material. In the first case, lithium inventory and anode active material decay sharply after the plummeting. In the second case that is more likely to occur at high temperature and high discharging current, the three aging modes all experience dramatic growth. By analyzing the commonalities of state-of-health indicator parameters evolution under the two capacity plummeting mechanisms, we propose the characterization of accelerated capacity deterioration and explore the identification method of capacity plummeting based on the cycling data.

Lifetime Rapid Evaluation Method for Lithium-Ion Battery with Li(NiMnCo)O2 Cathode

This paper conducts battery cyclic life tests under a full state-of-charge range (0-100%) and five partitioned state-of-charge ranges (0–20%, 20%–40%, 40%–60%, 60%–80% and 80%–100%). The attenuation of state-of-health indicator parameters along with cycle times under different state-of-charge ranges is compared. For the batteries cycled under 20% state-of-charge depth, loss of lithium inventory (LLI) is the leading factor resulting in capacity degradation. Expanding cycle state-of-charge depth accelerates the loss of electrode active material, but has little effects on LLI. When suffering identical cycle times, the sum of the decrements of state-of- health indicator parameter related to LLI under the five partitioned state-of-charge ranges is equal to 0–100% state-of-charge, which proves the additivity of LLI. Considering the linear correlation between capacity and state-of-health indicator parameters, a linear regression capacity model is established. Then, based on the additivity of LLI and capacity estimation model, an innovative evaluation method of battery lifetime with less testing time consumption is proposed, which conducts cycle aging tests under the partitioned state-of-charge ranges replacing full state-of-charge range to reduce testing time. Using this method, time consumption can be reduced by 75%, and the estimation error of capacity and lifetime is 3% and 10% respectively.

Overcharge investigation of large format lithium-ion pouch cells with Li(Ni0.6Co0.2Mn0.2)O2 cathode for electric vehicles: Thermal runaway features and safety management method

In this paper, the overcharge-induced thermal runaway features of large format commercial lithium-ion batteries with Li(Ni0.6Co0.2Mn0.2)O2 (NCM622) cathode for electric vehicles under different current rates (C-rates) have been systematically studied at ambient temperature. The overcharge process is characterized as four stages. The temperature rise and the maximum temperature of the battery surface don't increase in proportion to the applied C-rates. However, with the increase of C-rates, the crest voltage of voltage curve rises linearly. When the voltage reaches approximately 5.1 V, a new voltage plateau appears in the cases below 2C. It is not sufficient that the temperature sensor is placed only near the terminal tab for most battery packs of EVs. In addition, the accumulated heat analysis demonstrates that side reactions dominate the temperature rise and contribute to most of the accumulated heat before thermal runaway. To mitigate the impact of overcharge and avoid the thermal runaway risk, a safety management method is proposed. Furthermore, the sharp drop in voltage before thermal runaway also provides a feasible approach to forewarn the users of the impending risk. These results are important for building safer batteries and providing information for the safety monitoring function of the battery management system (BMS).

Synthesis of Li(Ni1/3Mn1/3Co1/3-xBax)O2 cathode materials for lithium-ion rechargeable battery by glycine-nitrate combustion process

This study was based on developing Li(Ni1/3Mn1/3Co1/3-xBax)O-2 (x=0.04, 0.08, 0.11, 0.22, and 0.33) materials by substituting expensive Co with Ba, for the use in the cathode of rechargeable lithium-ion batteries (LIBs). Glycine-nitrate combustion method, which is a low-cost combustion technique, was employed to synthesize spherical shaped micron size secondary particles formed by densely agglomerated primary particles. The phase analysis performed by the X-ray diffractometry revealed the formation of the required layered phase of R-3m structure with trace amounts of a secondary phase. Furthermore, these Ba-substituted novel materials showed considerably higher electrical conductivity than those of the Li(Ni1/3Co1/3Mn1/3)O-2 base material. In the cell performance studies, the Ba-substituted cathode materials synthesized in this study showed slightly lower initial discharge capacity of 162.4mAhg(-1) but with considerably improved cycle performance compared to those of the Li(Ni1/3Co1/3Mn1/3)O-2 base material (187.7mAhg(-1)). More importantly, the Li(Ni1/3Mn1/3Co1/3-xBax)O-2, x=0.04 material clearly showed its ability to eliminate and prevent structural transformation usually associated with excess Li extraction at potentials above 4.5V. Therefore, the Li(Ni1/3Mn1/3Co1/3-xBax)O-2, x=0.04 material can be proposed as a potential candidate for the high-voltage cathode application of LIB.

Lithium-Ion Battery Anodes of Stacked Nanowire Laminate for Ultrahigh Areal Capacities

Herein, a stacked Ge/Cu nanowire (NW) laminate made by stacking several Ge/Cu nanowire laminates accompanied by the conductive glue adhesives is used to achieve high capacity output per unit area (>10 mA h cm–2). The combination of Cu NWs and conductive adhesives constructs a tough and conducting network through the electrode, and the stacked Ge/Cu nanowire laminate electrodes can load an ultrahigh mass of 14.8 mg Ge per unit area and provide an areal capacity output over 16 mA h cm–2. A full-cell with an areal capacity of 11 mA h cm–2 built by stacked Ge/Cu nanowire laminate anode and Li(Ni0.5Co0.3Mn0.2)O2 cathode was prepared and used to supply electricity for electronic devices, demonstrating their potential to be a candidate anode for high areal capacity Li-ion microbatteries that can be used for high-tech and integrated microsystems with limited space.

Ti3C2(OH)2 coated Li(Ni0.6Co0.2Mn0.2)O2 cathode material with enhanced electrochemical properties for lithium ion battery

Ti3C2(OH)2 coated nickel-rich LiNi0.6Co0.2Mn0.2O2 cathode material is prepared with wet coating process. The effects of the Ti3C2(OH)2 concentration on the structure and electrochemical performance of LiNi0.6Co0.2Mn0.2O2cathode materials are investigated. The microanalyses show that Ti3C2(OH)2 is successfully coated on the surface of LiNi0.6Co0.2Mn0.2O2 cathode material. All cathode materials display the excellent hexagonal ordering and the low ratio of I(006+102)/I(101). Furthermore, the Ti3C2(OH)2 coated cathode materials presents excellent cycling capability and rate capability. Among them, the 3.0 wt.% Ti3C2(OH)2 coated LiNi0.6Co0.2Mn0.2O2 displays the highest discharge capacity of 124.5 mAh/g with the capacity retention of 86.4% after 200 cycles at 0.5 C, and the best rate performance at high current density. So Ti3C2(OH)2 coating is good promising material for LiNi0.6Co0.2Mn0.2O2 to improve the long-life and rate capability.

PVDF/Palygorskite Nanowire Composite Electrolyte for 4 V Rechargeable Lithium Batteries with High Energy Density.

Solid electrolytes are crucial for the development of solid state batteries. Among different types of solid electrolytes, poly(ethylene oxide) (PEO)-based polymer electrolytes have attracted extensive attention owing to their excellent flexibility and easiness for processing. However, their relatively low ionic conductivities and electrochemical instability above 4 V limit their applications in batteries with high energy density. Herein, we prepared poly(vinylidene fluoride) (PVDF) polymer electrolytes with an organic plasticizer, which possesses compatibility with 4 V cathode and high ionic conductivity (1.2 × 10-4 S/cm) at room temperature. We also revealed the importance of plasticizer content to the ionic conductivity. To address weak mechanical strength of the PVDF electrolyte with plasticizer, we introduced palygorskite ((Mg,Al)2Si4O10(OH)) nanowires as a new ceramic filler to form composite solid electrolytes (CPE), which greatly enhances both stiffness and toughness of PVDF-based polymer electrolyte. With 5 wt % of palygorskite nanowires, not only does the elastic modulus of PVDF CPE increase from 9.0 to 96 MPa but also its yield stress is enhanced by 200%. Moreover, numerical modeling uncovers that the strong nanowire-polymer interaction and cross-linking network of nanowires are responsible for such significant enhancement in mechanically robustness. The addition of 5% palygorskite nanowires also enhances transference number of Li+ from 0.21 to 0.54 due to interaction between palygorskite and ClO4- ions. We further demonstrate full cells based on Li(Ni1/3Mn1/3Co1/3)O2 (NMC111) cathode, PVDF/palygorskite CPE, and lithium anode, which can be cycled over 200 times at 0.3 C, with 97% capacity retention. Moreover, the PVDF matrix is much less flammable than PEO electrolytes. Our work illustrates that the PVDF/palygorskite CPE is a promising electrolyte for solid state batteries.

Dual Roles of Li3 N as an Electrode Additive for Li-Excess Layered Cathode Materials: A Li-Ion Sacrificial Salt and Electrode-Stabilizing Agent.

Li2 CO3 -passivated Li3 N with high stability is prepared by aging Li3 N powder in dry air, and is then used as an electrode additive for a Li(Li0.18 Ni0.15 Co0.15 Mn0.52 )O2 (LLMO) cathode material. The material shows a large irreversible capacity of 800 mA h g-1 during the first charge, with the formation of a Li2 N intermediate product. Acting as a Li+ sacrificial salt for a LLMO(+)/graphite(-) Li-ion battery, 2 wt % Li3 N results in a 10 % increase in discharge capacity. The Li2 N intermediate product reacts with the electrolyte, forming a uniform and regular surface film on the cathode. Moreover, chemical bonding between LLMO and N improves the electrode stability, resulting in excellent electrochemical performance.

Aging mechanisms under different state-of-charge ranges and the multi-indicators system of state-of-health for lithium-ion battery with Li(NiMnCo)O2 cathode

Understanding the degradation of battery cycled under different state-of-charge ranges is important for the optimal control of operation state-of-charge range. Cycle life tests on 8 A h pouch batteries with Li(NiMnCo)O2 cathode are conducted under 0–20%, 20%–40%, 40%–60%, 60%–80%, 80%–100% and 0–100% state-of-charge ranges with current and temperature at 6C and 25 °C. Results show that among the five ranges with 20% depth-of-discharge, cycling under 0–20% causes more impedance increase and less capacity loss, cycling under 80%–100% cause more capacity loss. The degradation behaviors of batteries under the remaining three ranges are similar. Battery degradation under 20% depth-of-discharge is significantly slower than 100% depth-of-discharge. Battery aging mechanisms are investigated using incremental capacity analysis method. It is indicated that loss of active material in positive electrode and loss of lithium inventory are comparable during battery aging process under 100% depth-of-discharge. However, for the battery under 20% depth-of-discharge, the dominant factor causing aging is loss of lithium inventory. Moreover, six characteristic parameters corresponding to loss of lithium inventory and loss of electrode material respectively are extracted from incremental capacity curve to establish the multi-indicators system describing battery state-of-health, which enhances the convenience of incremental capacity analysis to identify battery aging mechanisms on-board.

(Battery Division Technology Award) Insight of Structures and Properties of Cathode Materials for Li-ion Battery

Insight into relationship between Crystal/Interface structure and properties of capacity, stability and rate capability are important for developing advanced Li-ion batteries. Using theoretical calculations combined with experimental in-situ tests, we did extensive studies on the kinetic of Li-ion diffusion for two representative cathode materials: layered Li(NixMnyCoz)O2 (NMC) (x + y + z = 1) and LiFePO4. We not only focus on the bulk kinetics, but also the kinetics across electrode/electrolyte solid-liquid interface and in the electrolytes. For example, we first proposed that "Janus" solid-liquid interface would facilitate the Li-ion transport in battery and introducing some disordering in non-active cathode materials would activate them for Li-ion storage.（Ref. 1） For high energy and power density applications (e.g., EVs), the safety becomes especially important. Using ab initio calculations combined with experiments, we clarified how the thermal stability of NMC materials can be tuned by the most unstable oxygen, which is determined by the local coordination structure unit (LCSU) of oxygen (TM(Ni, Mn, Co)3-O-Li3-x’): each O atom bonds with three of transition metal (TM) from the TM-layer and three to zero of Li from fully discharged to charged states from the Li-layer. Under this model, how the lithium content, valence states of Ni, contents of Ni, Mn, and Co, and Ni/Li disorder to tune the thermal stability of NMC materials by affecting the sites, content, and the release temperature of the most unstable oxygen is proposed. In NMC, insight of Ni/Li disorder has be investigated by theory and experimental e.g. neutron powder diffraction experiments and magnetization measurements. The spins of TM ions construct a two-dimensional triangular networks, which can be considered as a simple case of geometrical frustration. Remarkably, the frustration parameters of these compounds are estimated to be larger than 30, indicating the existence of strongly frustrated magnetic interactions between spins of TM ions, which give rise to lattice instability, the formation of Li/Ni exchange in NMC will help to partially relieve the degeneracy of the frustrated magnetic lattice by forming a stable antiferromagnetic state in hexagonal sublattice with nonmagnetic ions located in centers of the hexagons. Moreover, Li/Ni exchange will introduce 180° superexchange interaction, which further relieves the magnetic frustration through bringing in new exchange paths. Thus, the variation of Li/Ni exchange ratio vs. TM mole fraction in NMC with different compositions can be well understood and predicted in terms of magnetic frustration and superexchange interactions. (Ref. 2) Ref. (a)F. Pan el al., “Kinetics Tuning of Li-ion Diffusion in Layered Li(NixMnyCoz)O2”, J. Am. Chem. Soc., 2015, 137, 8364; (b) "Optimized Temperature Effect of Li-Ion Diffusion with Layer Distance in Li(NixMnyCoz)O2 Cathode Materials for High Performance Li-Ion Battery", Adv. Energy Mater., 2015, 1501309(1-9).(c) "Janus Solid–Liquid Interface Enabling Ultrahigh Charging and Discharging Rate for Advanced Lithium-Ion Batteries", Nano Lett,2015, 15 (9), pp 6102 (d)“Single-particle performances and properties of LiFePO4 nanocrystals for Li-ion batteries” Energy Mater., (Front page ) 2016, 1601894 (e) Nano Lett, 2017, 17, 6018 (f) Nano Energy 2017 37, 90 (g) Nano Lett., 2017, 17 (8), 4934(a) F. Pan el al., “Tuning of Thermal Stability in Layered Li(NixMnyCoz)O2”, J. Am. Chem. Soc., 2016, 138 (40), 13326, (b)“Aligned Li+ Tunnels in Core−Shell Li(NixMnyCoz)O2@LiFePO4 Enhances Its High Voltage Cycling Stability as Li-ion Battery Cathode” Nano Letters 2016, 16 (10), pp 6357; (c) Nano Letters, 2015, 15, 5590; （d）The Role of Super-Exchange Interaction on Tuning of Ni/Li Disordering in Layered Li (NixMnyCoz) O2, J. Phys. Chem. Lett., 2017, 8 (22), 5537; (e) Insight into the origin of Lithium/Nickel ions exchange in layered Li(NixMnyCoz)O2 cathode materials, Nano Energy 49 2018,49,77

Highly Enhanced Cycleability from High Crystalline Biaxially Aligned CNT Web for Li-Air Cathode Applications

In recent years, Li-O2 batteries have attracted a great deal of attention due to the high theoretical capacity for applications as electronic vehicles. Carbon nanotubes are widely used as cathode materials for Li-O2 batteries because of their high conductivity, high surface area and low density. However, due to their hydrophobic surface properties and the high van der Waals interaction between their walls, they tend to aggregate on their own, failing full use of the CNT surface. Therefore, it is necessary to engineer the nanoscale space between the CNTs such that each CNT aligns with each other and the nanoscale spacing lies between them. In this way, it is possible for the ionic liquid electrolyte and oxygen to access individual CNTs and enable uniform Li2O2 formation. In this research, we developed a one-step process for biaxially oriented, highly crystalline CNT fabrics using a combination of floating catalyst chemical deposition (FCCVD) and one-step direct spinning technology. A highly crystalline DWCNT with a diameter of 6 nm was synthesized by FCCVD using ferrocene, thiophene, and methane, as precursors, and as-spun CNTs were woven into fabric by 2-directional spinning process. The intensity ratio between D and G bands (ID/IG) of 0.06 showed high crystallinity of CNT surface. The microscopic architectures of randomly oriented CNT fabric and biaxially oriented CNT fabric were investigated using a high-resolution scanning electron microscope (See Figure 1.(a) and (b)). The biaxial orientation was reconfirmed using a polarized Raman spectroscopy. In order to investigate the effect of the microscopic structure on the performance of the Li-O2 battery, we have assembled Li-O2 cells using a random CNT fabric and a biaxially aligned CNT fabric as a cathode. In the random CNT cathode, the charging overpotential gradually increases, leading to rapid decay of capacity upon cycling (Fig. 1(c)). The increase in overpotential is typically associated with the accumulation of insulating byproducts due to parasitic reactions involving the electrolyte or the carbon electrode. However, in the biaxially aligned CNT electrode, a much improved cycle stability and small charging overpotentials are demonstrated (Fig. 1.(d)). This dramatically improved cycling performance might result from the increase in the surface area corresponding to mesopores, providing more effective sites capable of carrying discharge products such as Li2O2. In addition, Li-O2 cathode using biaxially aligned CNT fabric can offer open framework in which O2 and electrolytes can access to the individual CNTs, facilitating reversible Li2O2 formation and removal, and consequently exhibiting enhanced cyclability. Figure 1

Singlet Oxygen in Non-Aqueous Battery Chemistries

The redox chemistry of O2 moieties has come into the focus of much of the forefront battery research such as metal-O2 batteries and Li-rich layered oxides (1, 2). O2 evolution is in either case a critical yet not fully understood phenomenon (1, 3). For example, operation of the rechargeable metal-O2 batteries depends crucially on the reversible formation/decomposition of metal (su)peroxides at the cathode on discharge/charge. The greatest challenge facing progress arises from severe parasitic reactions that decompose the electrolyte as well as the porous electrode. These processes have serious consequences. So far these parasitic reactions have been ascribed to the reactivity of superoxide and peroxide. Yet, their reactivity cannot consistently explain the observed irreversible processes. Unsurprisingly, strategies to mitigate the irreversibilities proved only partially successful. Therefore, only better knowledge of parasitic reactions may allow them to be inhibited. Here we discuss our recent insights into irreversible parasitic reactions caused by the highly reactive singlet oxygen (1O2) during cycling of non-aqueous batteries that have so far been overlooked. They account for the majority of the parasitic products on discharge and nearly all on charge in Li-O2 and Na-O2 cells (4-6). Moreover, singlet oxygen forms upon oxidizing Li2CO3 above 3.8 V vs Li/Li+ (7). Li2CO3 is a universal passivating agent in Li-ion battery cathodes and decisive in interfacial reactivity. It is also a common side product in Li-O2 cathodes, as well as the targeted discharge product in Li-O2/CO2 batteries. We will further discuss work on open question with respect to 1O2 non-aqueous battery chemistries such as catalysts, electrolytes, mediators, quenchers and other additives as well as the formation mechanism and the implications for metal-O2 cells and intercalation chemistries. Awareness of the highly reactive singlet oxygen gives a rationale for future research towards achieving highly reversible cell operation in a broad range of cell chemistries. References(1) Bruce, P. G.; Freunberger, S. A.; Hardwick, L. J.; Tarascon, J.-M. Nature Mater. 2012, 11, 19. (2) McCalla, E. et al.. Science 2015, 350, 1516. (3) Luo, K; et al. JACS 2016, 138, 11211 (4) Mahne, N., et al. Nature Energy 2017 , 17036. (5) L. Schafzahl, et al, Angew. Chem. Int. Ed., 2017, 56, 15728. (6) N. Mahne, O. Fontaine, M. Thotiyl, M. Wilkening & S. A. Freunberger, Chem. Sci., 2017, 8, 6716. (7) N. Mahne, S.E. Renfrew, B.D. McCloskey & S.A. Freunberger, Angew. Chem. Int. Ed., doi: 10.1002/anie.201802277.

(Invited) Rational Design of Battery Cathode Materials

We will discuss about applying ‘materials by design’ and validation experimental research on high capacity cathode materials for Li and Na ion batteries (LIB and NIB). Using the first-principles density functional theory (DFT) method, we have designed electrode materials for battery cathodes, and subsequently performed experimental studies to validate the material designs. Through an integrated material design - experiment research, we have developed highly efficient cathode materials for NIB. [1] Furthermore, using the DFT based stability analysis of Li(Ni,Mn,Co)O2 (NMC) cathode materials, the underlying mechanisms of stability change in Ni-rich NMC cathodes are elucidated over the range of 30 – 100 % Ni concentration in metal composition. [2-6] Surface analysis of Ni-rich NMC has also provided insights on the degradation mechanisms (both chemical and mechanical) facilitating to develop a design strategy to improve the stability of Ni-rich NMC over 80% Ni contents. [7] This work was also supported by the International Energy Joint R & D Program (No. 20168510011350) of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Ministry of Knowledge Economy, Korean government. [1] D. Kim, M. Cho, K. Cho, “Rational Design of Na(Li1/3Mn2/3)O-2 Operated by Anionic Redox Reactions for Advanced Sodium-Ion Batteries,” Adv Mater 29(33), 1701788 (2017). [2] Chaoping Liang, F, Kong, R. Longo, Santosh KC, Jeom-Soo Kim, SangHoon Jeon, SuAn Choi, K. Cho, “Unraveling the Origin of Instability in Ni-Rich LiNi1−2xCoxMnxO2 (NCM) Cathode Materials,” The Journal of Physical Chemistry C 120(12), 6383–6393 (Mar. 31, 2016) [3] R. C. Longo, F. Kong, C. Liang, D. -H. Yeon, J. Yoon, J. -H. Park, S. -G. Doo and K. Cho, “Transition Metal Ordering Optimization for High-Reversible Capacity Positive Electrode Materials in the Li-Ni-Co-Mn Pseudoquaternary System,” Journal of Physical Chemistry C 120(16), 8540-8549 (Apr. 28, 2016). [4] F. Kong, C. Liang, L. C. Roberto, D.-H. Yeon, Y. Zheng, J.-H. Park, S.-G. Doo and K. Cho, “Conflicting Roles of Anion Doping on the Electrochemical Performances of Li-ion Battery Cathode Materials”, Chem. Mater. 28(19), 6942–6952 (Oct. 11, 2016) [5] Chaoping Liang, Roberto C. Longo, Fantai Kong, Chenxi Zhang, Yifan Nie, Yongping Zheng, Jeom-Soo Kim, SangHoon Jeon, SuAn Choi, and K. Cho, “Obstacles toward unity efficiency of LiNi1-2xCoxMnxO2 (x=0~1/3) (NCM) cathode materials: Insights from ab initio calculations” Journal of Power Source 340, 217-228 (2017). [6] C. Liang, F. Kong, R. Longo, C. Zhang, Y. Nie, Y. Zheng, K. Cho, “Site-dependent multicomponent doping strategy for Ni-rich LiNi1-2yCoyMnyO2 (y=1/12) cathode materials for Li-ion batteries,” J. Mater. Chem. A 5(48), 25303-25313 (Dec. 2017). [7] C. Liang, R. Longo, F. Kong, C. Zhang, Y. Nie, Y. Zheng, K. Cho, “Ab initio Study on Surface Segregation and Anisotropy of Ni-rich LiNi1-2yCoyMnyO2 (NCM) (y ≤ 0.1) Cathodes,” ACS Appl. Mater. Inter. (2018).

(Battery Division Student Research Award sponsored by Mercedes-Benz Research & Development) Advanced Electrochemical Energy Storage Systems: Material Development, Alternative Electrode Processes & Planar Devices

Future advancements in energy storage systems (lithium-ion batteries/LIBs and beyond) rely on the development of novel materials, innovative electrode/device architectures and scalable processing techniques or a combination thereof. In this talk, I will discuss my work on each of these three aspects including in situ characterization of planar devices as well as the development of nanomaterials and additive-free electrode architectures via alternative manufacturing processes such as dry/cold pressing and extrusion printing, respectively. Operando studies can elucidate the reaction behavior of battery electrodes during operation; however, specialized electrochemical cells are required to study these materials in their natural environment (in situ). In this study, a planar microscale battery with an open cell configuration was designed to investigate the structural evolution and concomitant solid electrolyte interphase formation of model electrode-electrolyte systems, such as Na-MoS2.1 By coupling an atomic force microscope with the planar electrochemical cell platform, real-time topographical observations of MoS2 electrodes during sodiation are readily achieved, which leads to crucial information regarding battery operation at the nanoscale. The use of advanced in situ/operando techniques with this newly developed planar battery configuration can elucidate the electrochemical behavior of numerous electrode-electrolyte systems, particularly for alkali-metal-ion batteries, during cycling. The drive towards lighter electric vehicles with longer ranges requires the development of higher energy density systems beyond conventional LIBs, such as lithium-oxygen (Li-O2) batteries. To increase battery performance for practical applications, high mass loading electrodes are advantageous as long as optimal battery reactions are maintained throughout the entirety of the “thick” electrode. Here, I present a facile, alternative electrode processing method known as dry/cold pressing, where a highly porous and compressible carbon nanomaterial (holey graphene or hG) enables the formation of mechanically robust, high mass loading electrodes for Li-O2 batteries.2-3 Dry pressing hG, the compressible matrix, with incompressible materials also enables the preparation of unique mixed and stacked/sandwich electrode architectures under binder- and solvent-free conditions.3 The enhancements in electrochemical performance demonstrate the promise of dry pressed electrode architectures and the reported additive-free processing method for advanced electrochemical energy storage systems. Additive manufacturing (AM) techniques also show promise towards the fabrication of complex 3D designs for advanced electrochemical devices. In particular, the development of inexpensive, sustainable (aqueous), and easily processable material ink systems and the use of a facile and low-cost fabrication process, such as extrusion-based 3D printing, are advantageous for scalable battery manufacturing. In this work, hierarchically porous electrode architectures are readily extruded using additive-free, aqueous graphene oxide-based (GO) ink compositions and demonstrated as the first 3D printed Li-O2 cathodes.4 The development of a nanoporous GO material enabled trimodal porosity (nano-micro-macropores) within the 3D printed mesh architecture, which provides facile mass/ionic transport pathways and enhances active-site utilization during battery operation. The results demonstrate the potential of AM techniques towards the scalable fabrication and improvement of advanced energy storage devices through structurally conscious designs as well as tailored material compositions.

Influence of precursor phase on the structure and electrochemical properties of Li(Ni0.6Mn0.2Co0.2)O2 cathode materials

LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode materials are prepared via sintering the mixtures of (Ni0.6Mn0.2Co0.2)(OH)2 precursor and LiOH. The effects of the β-(Ni0.6Mn0.2Co0.2)(OH)2 content in hydroxide precursor on the structure and electrochemical performance of NCM622 cathode materials are investigated. Among three kinds of cathodes, the cathode material sintered from β-(Ni0.6Mn0.2Co0.2)(OH)2 phase precursor exhibits the excellent layered structure with the highest c/a value. Furthermore, it displays the excellent hexagonal ordering with the lowest ratio of I(006+102)/I(101). With increasing the β-(Ni0.6Mn0.2Co0.2)(OH)2 phase content in precursors, the discharge capacity of NCM622 samples first increases, and then decreases. The cathode material sintered from the mixed phase of α-(Ni0.6Mn0.2Co0.2)(OH)2 and β-(Ni0.6Mn0.2Co0.2)(OH)2 shows the highest discharge capacity of 192.1mAh/g and best rate performance, and then is the best recommendation for a high-power cathode. While the cathode material sintered from single β-(Ni0.6Mn0.2Co0.2)(OH)2 phase shows the best cycle stability and the capacity retention of 91.7% after 100 cycles, and then is the best recommendation for a long-life cathode.

Effect of Water and HF on the Distribution of Discharge Products at Li–O2 Battery Cathode

Li–air battery has attracted much attention because of its very high theoretical energy density, but its actual performance is still very low. Most important reasons are the slow kinetics and low reversibility of electrodeposition/dissolution of Li–O2 species at the cathode. Thus, much effort has been devoted to understand the mechanisms of these processes but low reproducibility makes the full understanding of the mechanism difficult. Here we demonstrate that low reproducibility is caused by impurities in solution by showing how HF and H2O, major impurities, affect the potential dependent product distribution during discharge at Li–O2 cathode. HF causes significant mass increase as a result of the deposition of fluorine-containing species and H2O converts Li2O2 to proton containing side products such as H2O2, LiHO2, and LiOH and induces the solvent, DMSO, decomposition. These results demonstrate the importance of the impurity control in the operation of Li–air battery.

Assessing the potential of a hybrid battery system to reduce battery aging in an electric vehicle by studying the cycle life of a graphite∣NCA high energy and a LTO∣metal oxide high power battery cell considering realistic test profiles

The utilization of a hybrid battery system (combination of different battery packs via dc/dc converter) in an electric vehicle application is discussed. It is investigated whether battery aging in an electric vehicle can be reduced by using a hybrid battery system. Cycle aging measurements of lithium-ion battery cells were performed at 23 °C against the background of the latter application. Recommendations for hybrid battery system electric vehicle operation are given. For Panasonic NCR 18650 BD cylindrical high energy cells (graphite anode, Li(NiCoAl) O2 cathode), three cycle aging campaigns were conducted systematically, evaluating the impact of charging as well as discharging loads with different time scales and microcycling per driving distance. A significant impact of recuperation pulse duration on aging per driving distance could be observed, whereas varied discharge load characteristics did not vary the aging characteristics. On the basis of differential open circuit voltage analysis, possible degradation mechanisms are discussed. The main driver of capacity loss and resistance increase in cycle aging campaigns with real world driving cycles appears to be the loss of cyclable lithium. Within the operating conditions investigated here, anode aging is intensified with increasing recuperation pulse duration. Another cycle aging campaign with symmetric current rate of 10C for a prismatic high power battery cell (Li4Ti5O12 anode, metal oxide cathode) yielded excellent cycle performance of this cell.

Toward True Lithium-Air Batteries

Lithium-oxygen batteries with high energy densities are limited by pure oxygen feeding and side reactions that hinder their practical applications. In a recent Nature paper, Asadi et al. proposed powerful designs in a lithium-oxygen battery that offers an excellent cycle life in air-like atmosphere, a step closer to true lithium-air batteries.

Synthesis and Characterization of Li(Li0.05Ni0.6Fe0.1Mn0.25)O2 Cathode Material for Lithim Ion Batteries

A new type of lithium enriched cathode material Li (Li0.05Ni0.6Fe0.1Mn0.25)O2 was synthesized by sol-gel method with citric acid as a chelating agent. The structural and morphological studies were systematically investigated through X-ray diffraction, SEM with EDS, FT-IR and Raman analyses. The crystallite size of the Li (Li0.05Ni0.6Fe0.1Mn0.25)O2 cathode material was found to be 45 nm thereby leads to the feasible movement of lithium ion all through the material. FT-IR spectroscopy was used to confirm the metal-oxygen interaction in the prepared cathode material. The electrical properties of the Li (Li0.05Ni0.6Fe0.1Mn0.25)O2 cathode material were studied by impedance and dielectric spectral analyzes. Li (Li0.05Ni0.6Fe0.1Mn0.25)O2 showed a maximum ionic conductivity of 10-6 S/cm at ambient temperature.