Ni-rich Materials Research Articles

High Nickel Positive Electrode Materials Modified By Dry Particle Fusion

High-energy-density Ni-rich cathode materials suffer from the critical challenge of poor capacity retention due to micro-cracking and interfacial reactivity with electrolyte. Addition of foreign elements to some Ni-rich materials is known to stabilize their capacity over cycling. In this work, we established that the benefit of these elements coating on Ni-rich hydroxide precursors before synthesis is universal in presence of major dopants used in Ni-rich materials in terms of improving the capacity retention of Co-free Ni-rich polycrystalline materials. Experimental characterization and theoretical modelling suggested some new perspectives on the location of these foreign elements along with their morphology control of primary particles and the working mechanism for superior performance.

(Digital Presentation) Mapping of Degradation Processes in Ni-Rich Layered Oxide Cathode Materials in State-of-the-Art Commercial Li-Ion Cells Based on Battery Usage Conditions

Ni-rich oxide cathode active materials are today key components in Li-ion batteries used for electric vehicles (EV). The high capacity of LiNixCoyMnzO2 and LiNixCoyAlzO2 (NCA) with x≥0.6 has enabled a continued increase in energy density and decrease in cost at the pack level, enabling the rapid growth of the EV market in recent years. Despite a wide use, rather fast material ageing results in the batteries being a source of considerable environmental impact [1]. Various degradation sources are highlighted in the literature, these include transition metal dissolution, surface layer reconstruction, particle cracking, etc [2]. However, when extrapolating the knowledge from a model cell to a commercial battery the relevance and the degree of degradation impact can drastically change [3]. The importance of approaching real conditions is a key to a full understanding of the ageing processes occurring in commercial cells. In the given work, we analyse commercial state-of-art 2170 cylindrical cells. The cells were aged at various temperatures and state of charge windows, targeting divergent usage scenarios. The degradation processes were accessed with a wide range of analytical techniques applied to extracted electrodes (x-ray diffraction, inductively coupled plasma atomic emission spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, cycling voltammetry, incremental capacity analysis, electrochemical impedance spectroscopy and intermittent current interruption). In the current work we show that depending on the operating conditions, influence of ageing sources varies. Additionally, ageing mapping within cell geometry is presented highlighting “hot spots” of the cell [4].

Investigating Surface Sensitivity of Ni-Rich Cathode Material Towards CO2 and H2O

Layered Ni-rich transition metal oxide materials have been considered as the most promising cathode utilized in Li-ion batteries, e.g., LiNi0.8 Mn0.1 Co0.1 O2 (NMC 811). However, one of the drawbacks of NMC 811 is its high air sensitivity, leading to a degradation layer forming on the surface, and a lower cycling performance. Since the degradation mechanism is not fully understood, in this work, we use ambient pressure photoelectron spectroscopy (APPES)1 to investigate the surface sensitivity of NMC 811 towards CO2 and H2O in situ, aiming to determine the factor triggering the degradation. Before gas exposure, NMC 811 surface was Ar+ sputtered to remove the pre-existing boron oxide coating. The changes in surface chemical composition were monitored as a function of time and gas pressure. Results show that carbonate compounds are formed on the surface when NMC 811 is exposed to CO2. The carbonate compounds start to appear already within 2 minutes in CO2 at around 10-5 mbar. More interestingly, this reaction is reversed at around 3x10-6 mbar. Changes induced by water are slower, however, the water vapour effect on NMC 811 surface is irreversible. Results indicate that lithium hydroxide is formed, where Li+/H+ exchange on the surface is a possible route.2 Kokkonen, E.; Lopes Da Silva, F.; Mikkelã, M.-H.; Johansson, N.; Huang, S.-W.; Lee, J.-M.; Andersson, M.; Bartalesi, A.; Reinecke, B. N.; Handrup, K.; Tarawneh, H.; Sankari, R.; Knudsen, J.; Schnadt, J.; Såthe, C.; Urpelainen, S., Upgrade of the SPECIES beamline at the MAX IV Laboratory. Journal of Synchrotron Radiation 2021, 28 (2), 588-601.Hartmann, L.; Pritzl, D.; Beyer, H.; Gasteiger, H. A., Evidence for Li+/H+ Exchange during Ambient Storage of Ni-Rich Cathode Active Materials. Journal of The Electrochemical Society 2021, 168 (7), 070507. Figure 1

Dry Particle Fusion Assisted Ceramic Coatings for High Nickel Cathode for Scalable 18650 Lithium-Ion Batteries

Over the last several decades, energy storage has become one of the central tools for facilitating energy transformation from (electro)chemical reactions to electricity. Rechargeable lithium-ion batteries (LIBs) are among the most popular and promising mature technologies for portable electronics, grids, and transportation. The cathode, a working horse, mainly determines the overall capacity among the various components. Off-late layered Li-rich or Ni-rich material plays a vital role, especially Ni-rich LiNixMnyCo1-x-yO2; x ≥ 0.8 (NMC) get significant attention. However, it is unfortunate that such Ni-rich cathode materials encountered severe capacity degradation and poor thermal instability concerning the Ni-concentration. Several strategies have already been proposed to mitigate those issues, including electrolyte additive, cation doping, and coating or surface modification. Among them, the modification of the cathode surface, like core-shell construction, is a practical approach. Herein, a core-shell architecture was achieved by employing the cost-effective dry particle fusion method over Ni-rich (LiNi0.8Mn0.1Co0.1O2 (NMC811), where the nano aluminum oxide was used as a shell material with an average thickness of 150-200 nm. Such NMC@alumina core-shell exhibits excellent cycling stability compared with pristine NMC811. The chemical lithium diffusion coefficient was calculated using galvanostatic (GITT) and the potentio-dynamics process. Additionally, the control of parasitic reaction between the delithiated cathode and electrolyte was analyzed using the in-situ Differential Electrochemical Mass Spectrometry (DEMs) technique, where the onset potential and the amount of gas generated are compared with pristine material.

(Digital Presentation) Activating the Ion Transmission at the Cathode-Electrolyte Interface in All-Solid-State Batteries

All-solid-state batteries (ASSBs) have garnered increasing attention due to the enhanced safety, featuring nonflammable solid electrolytes as well as the potential to achieve high energy density. 1 The advancement of the ASSBs is expected to provide, arguably, the most straightforward path towards practical, high-energy, and rechargeable batteries based on metallic anodes.1 However, the sluggish ion transmission at the cathode-electrolyte (solid/solid) interface would result in the high resistant at the contact and limit the practical implementation of these all solid-state materials in real world batteries.2 Several methods were suggested to enhance the kinetic condition of the ion migration between the cathode and the solid electrolyte (SE).3 A composite strategy that mixes active materials and SEs for the cathode is a general way to decrease the ion transmission barrier at the cathode-electrolyte interface.3 The active material concentration in the cathode is reduced as much as the SE portion increases by which the energy density of the ASSB is restricted. In addition, the mixing approach generally accompanies lattice mismatches between the cathode active materials and the SE, thus providing only limited improvements, which is imputed by random contacts between the cathode active materials and the SE during the mixing process. Implementing high-pressure for the electrode and electrolyte of ASSB in the assembling process has been verified is a but effective way to boost the ion transmission ability between the cathode active materials and the SE by decreasing the grain boundary impedance. Whereas the short-circuit of the battery would be induced by the mechanical deformation of the electrolyte under high pressure. 4 Herein, we demonstrate a novel way to address the ion transmission problem at the cathode-electrolyte interface in ASSBs. Starting from the cathode configuration, the finite element method (FEM) was employed to evaluate the current concentration and the distribution of the space charge layer at the cathode-electrolyte interface. Hierarchical three-dimensional (HTD) structures are found to have a higher Li+ transfer number (tLi+), fewer free anions, and the weaker space-charge layer at the cathode-electrolyte interface in the resulting FEM simulation. To take advantage of the HTD structure, stereolithography is adopted as a manufacturing technique and single-crystalline Ni-rich (SCN) materials are selected as the active materials. Next, the manufactured HTD cathode is sintered at 600 °C in an N2 atmosphere for the carbonization of the resin, which induces sufficient electronic conductivity for the cathode. Then, the gel-like Li1.4Al0.4Ti1.6(PO4)3 (LATP) precursor is synthesized and filled into the voids of the HTD structure cathode sufficiently. And the filled HTD structure cathodes are sintered at 900 °C to achieve the crystallization of the LATP gel. Scanning transmission electron microscopy (STEM) is used to unveil the morphology of the cathode-electrolyte interface between the sintered HTD cathode and the in-situ generated electrolyte (LATP). A transient phase has been found generated at the interface and matched with both lattices of the SCN and the SE, accelerating the transmission of the Li-ions, which is further verified by density functional theory calculations. In addition, Electron Energy Loss Spectroscopy demonstrates the preserved interface between HTD cathode and SEs. Atomic force microscopy is employed to measure the potential image of the cross-sectional interface by the peak force tapping mode. The average potential of modified samples is lower than the sample that mix SCN and SEs simply in the 2D planar structure, which confirms a weakened space charge layer by the enhanced contact capability as well as the ion transmission ability. To see if the demonstrated method is universally applicable, LiNi0.8Co0.1Mn0.1O2 (NCM811) is selected as the cathode active material and manufactured in the same way as the SCN. The HTD cathode based on NCM811 exhibits higher electrochemical performance compared with the reference sample based on the 2D planar mixing-type cathode. We believe such a demonstrated universal strategy provides a new guideline to engineer the cathode/electrolyte interface by revolutionizing electrode structures that can be applicable to all-solid-state batteries.Figure 1. Schematic of comparing of traditional 2D planar cathode and HTD cathode in ASSB Tikekar, M. D., et al., Nature Energy (2016) 1 (9), 16114 Banerjee, A., et al., Chem Rev (2020) 120 (14), 6878 Chen, R., et al., Chem Rev (2020) 120 (14), 6820 Cheng, X., et al., Advanced Energy Materials (2018) 8 (7) Figure 1

(Invited) Thermal Properties of NMC Cathode Materials

NMC (LiNixMnyCozO2; x+y+z»1) materials deliver high capacity and excellent performance when used as cathodes in lithium-ion batteries. Increasing demand for higher energy density and concerns about the cost and ethics of using cobalt have prompted battery manufacturers to use Ni-rich formulations such as LiNi0.6Mn0.2Co0.2O2 (NMC622) and LiNi0.8Mn0.1Co0.1O2 (NMC811). The thermal stability of (partially) delithiated NMCs is known to decrease with increasing Ni content, however, so that scenarios of fires and other safety events become more distinct possibilities. To investigate the thermal properties of Ni-rich NMCs, we prepared partially and fully delithiated Ni-rich NMCs corresponding to various states-of-charge by chemical methods. We then studied the bulk and surface properties of these materials as they were heated or after they were heated, using a variety of ex situ and in situ synchrotron methods to understand the chemical changes that occur. Of particular concern are reactions that result in release of oxygen. Heated materials progress through a series of bulk structural changes from layered to spinel to rock salt as temperatures rise. Transition temperatures depend on both lithium and nickel content, with bulk changes evident at temperatures as low as 150°C. Surface-sensitive techniques such as soft X-ray absorption spectroscopy (sXAS) indicate that subtle changes that lead to oxygen release can happen well below these temperatures. The thermal behavior of the Ni-rich materials is very complex, and involves lattice transformation, transition metal migration and valence change and lithium redistribution. Moreover, these changes are dependent upon primary particle size, with smaller particles reacting at lower temperatures than larger ones. These observations suggest that materials can be engineered (through primary particle size manipulation, for example) to improve thermal robustness, and therefore, safety and reliability of lithium-ion batteries.

Mitigating the Surface Reconstruction of Ni-Rich Cathode via P2-Type Mn-Rich Oxide Coating for Durable Lithium Ion Batteries.

Ni-rich materials have received widespread attention as one of the mainstream cathodes in high-energy-density lithium-ion batteries for electric vehicles. However, Ni-rich cathodes suffer from severe surface reconstruction in a high delithiation state, constraining their rate capabilities and life span. Herein, a novel P2-type NaxNi0.33Mn0.67O2 (NNMO) is rationally selected as the surficial modification layer for LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode, which undergoes a spontaneous Na+-Li+ exchange reaction to form an O2-type LixNi0.33Mn0.67O2 (LNMO) layer revealed by combining X-ray diffraction and solid-state nuclear magnetic resonance techniques. Owing to the specific oxygen stacking sequence, O2-type LNMO significantly prevents the initial layered structure of NCM811 from transforming to the spinel or rock-salt phases during cycling, thus effectively maintaining the integral surficial structure and the Li+ diffusion channels of NCM811. Eventually, the NNMO@NCM811 electrode yields enhanced thermal stability, outstanding rate performance, and long cycling stability with 80% capacity retention after 294 cycles at 200 mA g-1, and its life span is further extended to 531 cycles while enhancing the mechanical stability of the bulk material.

Sr-Based Sub/Surface Integrated Layer and Bulk Doping to Enhance High-Voltage Cycling of a Ni-Rich Cathode Material

LiNi0.8Co0.1Mn0.1O2 (NCM) can achieve a high capacity of more than 200 mAh g–1 at charging voltages above 4.5 V, but it suffers from severe capacity fading at a high voltage during cycling associated with the lattice oxygen evolution-induced phase and surface structure modifications. Therefore, the big challenge for improving electrochemical performance is suppressing the lattice oxygen loss at a high voltage. Here, a facile strategy to inhibit the lattice oxygen loss of a Ni-rich material at a high charging voltage by a simple Sr treatment method is reported. The Sr treatment leads to the formation of a Sr-based sub/surface integrated layer and induces the atomic rearrangement on the subsurface to form Sr-based perovskite-like LixSr1–xTMO3 (TM = Ni, Co and Mn) during the heat treatment process. The perovskite-like structure can adsorb the oxidized Oα– to oxygen vacancies, transplant the pumped charges from the oxidized Oα–, and reduce them back to O2– to inhibit the movement of oxidized oxygen anions at the charged NCM surface. Furthermore, the formed Sr1–xHPO4 outer layer can prevent NCM from corroding by HF in organic electrolytes. Meanwhile, bulk doping stabilizes the metal–oxygen bond by suppressing the Ni migration at a high charging voltage. The modified NCM thus exhibited a significantly enhanced high-voltage cycle stability with 82.3 and 80.1% of capacity retentions at 1C achieved after 250 cycles at 25 °C and 100 cycles at 60 °C, respectively. This work opened a new avenue to suppress the lattice oxygen loss via surface structure regulations in high-energy-density rechargeable batteries during high-voltage cycling.

Effects of Co/Mn Content Variation on Structural and Electrochemical Properties of Single-Crystal Ni-Rich Layered Oxide Materials for Lithium Ion Batteries.

The development of single-crystal nickel-rich layered LiNixCoyMn1-x-yO2 materials (S-NCMs) represents the most significant progress for the electrification applications of nickel-rich ternary materials. There has been prior research on the important role of transition metal elements in agglomerated materials, supplemented by surface and internal lattice optimization to drive the performance improvements. However, studies on S-NCMs, especially on the role of transition metals (TM, i.e., Co and Mn), have not been reported. In this study, we synthesized four kinds of S-NCMs with different Co/Mn contents and studied their structural, electrochemical, kinetic, and thermodynamic properties with different Co/Mn contents. The results were as follows: (1) Electrochemically, Co was more effective than Mn at 25 °C at enhancing the intercalation/deintercalation kinetics, which resulted in an increased discharge capacity, an improved rate capability, and a reduced energy loss. (2) Thermodynamically, Mn was more effective at maintaining a higher thermal stability than Co, especially at a low cutoff voltage, but at a high cutoff voltage, the difference between the action of Co and Mn decreased. The main finding of this work was the enhanced structural stability provided by Co, which could be attributed to the following: (i) the absence of the H2/H3 phase transformation when Co exceeded 15%, which inhibited the irreversible phase transformation and reduced the volume strain, and (ii) the lower degrees of decrease in the cell parameters a and c with higher contents of Co, which contributed to a low cracking degree along the (003) crystal plane. The current work provides an important reference for the single-crystallization strategy of nickel-rich materials.

A low-temperature coating method with H3BO3 for enhanced electrochemical performance of Ni-rich LiNi0.82Co0.12Mn0.06O2 cathode

Layered LiNixCoyMn1−x−yO2 (NCM) materials have shown great potential in the field of electric vehicles. However, the increasing nickel content in Ni-rich ternary materials causes a dramatic degradation in their capacity retention. Meanwhile, the poor structure stability, as well as the high amount of residue lithium, give rise to the concerns of safety issues. Here, we put forward a simple method to convert residue lithium to coating compounds by directly mixing the LiNi0.82Co0.12Mn0.06O2 powders with boron acid and then getting the mixture heated at a low temperature. Transmission electron microscopy (TEM) and X-ray photoelectron spectrum (XPS) prove that the boron-contained compounds are successfully introduced to the surface of the matrix. The electrochemical performance of the boron-coated sample presents great improvement with a capacity loss of less than 2% and a distinctly suppressed electrochemical resistance increase after cycling at 1C for 100 times. This study demonstrates that the boron-contained coatings give effective protection to Ni-rich cathode materials and the low-temperature heating process seems to be an ideal treatment to endow the boron-coated materials with better electrochemical performance.

Storage degradation mechanism of layered Ni-rich oxide cathode material LiNi0.8Co0.1Mn0.1O2

With advantages such as high specific capacity and low cost, Ni-rich layered oxides are considered to be ideal cathode materials for power batteries. However, due to the high sensitivity of materials to air, structural degradation occurs during transportation and storage, resulting in the formation of an impurity layer. The degradation of the structure will weaken the comprehensive properties of Ni-rich cathode materials. The impurity layer will bring difficulties to the subsequent electrode manufacturing process, which seriously limits the practical application of Ni-rich materials. Therefore, it is particularly important to explore the storage decline mechanism of Ni-rich materials. Herein, the decay mechanism of structure and electrochemical properties of LiNi0.8Co0.1Mn0.1O2 materials after storage at room temperature and high humidity and high-temperature and humidity were studied. It is found that the instability of Ni3+ leads to the appearance of NiO rock salt phase on the surface of the material, accompanied by the formation of reactive oxygen species. Lithium and reactive oxygen species in the material react with H2O and CO2 in the air to form surface residual lithium compounds. The formation of the inert NiO layer and residual lithium compounds hinders the diffusion kinetics of Li+, resulting in serious capacity loss. During the high-temperature storage process, the material forms thicker residual lithium compounds, which aggravates the decay process. After 28 days of high-temperature storage, a residual lithium compound layer of about 7 nm thickness was formed, which seriously hindered the transmission of Li+. This study is helpful to deeply understand the storage failure behavior of Ni-rich cathode materials and promote the large-scale industrial production and application of Ni-rich cathode materials.

B2O3/LiBO2 dual-modification layer stabilized Ni-rich cathode for lithium-ion battery

Ni-rich layered oxide material with high theoretical capacity and low cost is one of the most promising cathode candidates for high-energy-density lithium-ion battery. However, increase of Ni content triggers structural instability and fast capacity degradation, which severely impedes the practical application of Ni-rich materials. Here, a surface dual-modification layer of B2O3 & LiBO2 is introduced to Ni-rich material LiNi0.89Co0.08Mn0.03O2 (NCM89), which successfully stabilizes the layered structure of NCM89 during cycling as well as removes residual lithium in NCM89. The in-situ X-ray diffraction and cross-sectional scanning electron microscopy results demonstrate effectively improved structural reversibility and stability of the cathode. Moreover, the dissolution of transition metals and decomposition of electrolyte at the cathode/electrolyte interface are successfully suppressed, resulting in beneficial cathode electrolyte interphase (CEI) layer. As a result, the boron modified cathode exhibits s a high capacity of 180.4mAh g−1 along with an excellent capacity retention of 90% after 100 cycles at 1C in 2.75–4.35 V at 25 °C, while the pristine NCM89 cathode only retains 59% of its initial capacity after 100 cycles. Furthermore, the capacity retention of full cell after 350 cycles is improved from 52.5% to 90%.

Surface Coupling between Mechanical and Electric Fields Empowering Ni-Rich Cathodes with Superior Cyclabilities for Lithium-Ion Batteries.

Ni‐rich cathodes with high energy densities are considered as promising candidates for advanced lithium‐ion batteries, whereas their commercial application is in dilemma due to dramatic capacity decay and poor structure stability stemmed from interfacial instability, structural degradation, and stress–strain accumulation, as well as intergranular cracks. Herein, a piezoelectric LiTaO3 (LTO) layer is facilely deposited onto Li[Ni x CoyMn1− x − y ]O2 (x = 0.6, 0.8) cathodes to induce surface polarized electric fields via the intrinsic stress–strain of Ni‐rich active materials, thus modulating interfacial Li+ kinetics upon cycling. Various characterizations indicate that the electrochemical performances of LTO‐modified cathodes are obviously enhanced even under large current density and elevated temperature. Intensive explorations from in situ X‐ray diffraction technique, finite element analysis, and first‐principle calculation manifest that the improvement mechanism of LTO decoration can be attributed to the enhanced structural stability of bulk material, suppressed stress accumulation, and regulated ion transportation. These findings provide deep insight into surface coupling strategy between mechanical and electric fields to regulate the interfacial Li+ kinetics behavior and enhance structure stability for Ni‐rich cathodes, which will also arouse great interest from scientists and engineers in multifunctional surface engineering for electrochemical systems.

Mg,Ti-base surface integrated layer and bulk doping to suppress lattice oxygen evolution of Ni-rich cathode material at a high cut-off voltage

The Nickel-rich layered cathode materials charged to 4.5 V can obtain a specific capacity of more than 200 mAh g−1. However, the nickel-rich layered cathode materials suffer from the severe capacity fade during high-voltage cycling, which is related to the phase transformation and the surface sides reactions caused by the lattice oxygen evolution. Here, the simultaneous construction of a Mg, Ti-based surface integrated layer and bulk doping through Mg, Ti surface treatment could suppress the lattice oxygen evolution of Ni-rich material at deep charging. More importantly, Mg and Ti are co-doped into the particles surface to form an Mg2TiO4 and Mg0.5–xTi2–y(PO4)3 outer layer with Mg and Ti vacancies. In the constructed surface integrated layer, the reverse electric field in the Mg2TiO4 effectively suppressed the outward migration of the lattice oxygen anions, while Mg0.5–xTi2–y(PO4)3 outer layer with high electronic conductivity and good lithium ion conductor could effectively maintained the stability of the reaction interface during high-voltage cycling. Meanwhile, bulk Mg and Ti co-doping can mitigate the migration of Ni ions in the bulk to keep the stability of transition metal–oxygen (M−O) bond at deep charging. As a result, the NCM@MTP cathode shows excellent long cycle stability at high-voltage charging, which keep high capacity retention of 89.3% and 84.3% at 1C after 200 and 100 cycles under room and elevated temperature of 25 and 55 °C, respectively. This work provides new insights for manipulating the surface chemistry of electrode materials to suppress the lattice oxygen evolution at high charging voltage.

A Cobalt Enrichment Strategy for Suppressing the 4.2 V Adverse Phase Transition in Ni-Rich Layered Materials

In this study, a Co-rich Ni-rich layered material with a core–shell structure is designed, in which LiNi0.82Co0.12Mn0.06O2 (NCM-Ni82) is used as the core wrapped in the shell by doping Al into LiNi0.735Co0.15Mn0.1Al0.015O2 to form the hybrid particle LiNi0.795Co0.13Mn0.07Al0.005O2 (NCM-HA). NCM-HA is divided modularly into the core part NCM-Ni82 and the single hybrid part without doped Al (NCM-HS), and then all modules were compared with the pristine LiNi0.8Co0.1Mn0.1O2 via various characterization methods to reveal the superiority of the design. The core–shell structure, which prevents the diffusion of microcracks caused by the lattice shrinkage of a high content of cobalt, is used to improve the morphological strength of the material so that the cathode material is capable of fully playing the excellent stable cycling performance brought by the remarkable cationic order degree of Co-rich treatment. The excellent cathode material NCM-HA still has a capacity retention rate of 83.35% after 200 cycles, while the pristine material has a rate of 55.42%. Moreover, NCM-HA successfully inhibits the unsteady phase transition of layered materials at 4.2 V and reduces the degree of polarization during the cycling process. This study provides a new strategy for the modification of Cobalt-enriched Ni-rich layered materials.

Concealed Cathode Degradation in Lithium-Ion Cells with a Ni-Rich Oxide

Difficulties with sourcing cobalt and the interest in increasing cell energy have motivated the development of Ni-rich oxide materials for lithium-ion battery cathodes. Despite the intense research on the topic, there is limited information available on the long-term performance of novel cathode formulations. Here, we evaluate the stability of LiNi0.9Mn0.05Co0.05O2 in full-cells tested for over five months, assessing how cycling, voltage and electrolyte additives impact cathode aging. We use differential voltage analysis to extract insights about the cathode from the full-cell data and identify the isolation of cathode particles in the delithiated (charged) state as a relevant mode of aging. Importantly, this particular mechanism of cathode aging does not cause immediate cell capacity fade, causing the simple analysis of cell capacity retention to overestimate the cathode stability under the investigated conditions. Our observations serve as cautionary tale indicating that careful analysis of data from extended testing may be required for assessing the performance of Ni-rich cathodes and for evaluating how these materials are affected by electrolyte additives.

New stepwise potentiostatic charge protocol for preventing dendrite formations in Li metal batteries

Here, we report a new charge protocol for dendrite-free Li-metal battery based on the understanding the effects of over-potential on Li dendritic growth. We demonstrate that when a large over-potential is applied, the deposited Li metal shows a needle-like morphology even though a current density of a cell does not reach the limiting current density. This clearly indicates over-potential leads to the early formation of space charge region near a negative electrode, and thereby the Li dendritic growth can be easily triggered. As a result, control of the over-potential is very important for dendrite-free Li metal batteries. Through this understanding, we propose a new stepwise potentiostatic charge protocol that can keep the over-potential below a certain critical value. By applying new charge protocol, we clearly demonstrate that Ni-rich layered materials can be fully utilized without triggering the Li dendritic growth. The understanding and finding provide a novel guideline and stimulate further research to develop ways to safely operate high energy density Li metal battery.

Effect of Sodium in LiNi0,5Mn0,3Co0,2O2 as a Lithium Ion Battery Cathode Material by Solid State Reaction Method

Abstract. Lithium-ion batteries (LIBs) have become widely used powder sources for portable electronics and electric vehicles. The discovery of lithium nickel manganese cobalt oxide (LiNi0.5Mn0.3Co0.2O2, NMC532), tremendous efforts have been paid to the development of Ni-rich layer-structured NMC532 materials due to its high capacity when charged to potentials higher than 4.3 V vs Li+/Li. In this work we report effect of Sodidium in NMC532 layer, the characterization was done by using X-Ray Diffractometer (XRD) to investigate the crystal structure, Electrochemical impedance spectroscopy (EIS) was used to illustrate the resistance change during cycling. The particles morphology and surface chemistry characterizations of both cathode and anode electrodes were performed on Scanning Electron Microscope (SEM). The XRD pattern of the sample shows diffraction peaks at 2θ = 18.663 o, 36.773 o, 44.459 o, 48.611 o, 58.604 o, 64.322 o, 65.069 o, 68.339 o and 77.798 o. Na does not affect the NMC532 lattice parameters, which means that Na which is expected to substitute for Li does not occur. The NMC532 conductivity with the addition of Na=0.03 showed a slightly lower value than the NMC532 conductivity with the addition of Na=0.01. Meanwhile, the highest conductivity was seen at NMC532 with the addition of Na=0.05. The addition of Na to NMC532 did not increase the conductivity linearly. SEM images of NMC532 and NMC532 with the addition of Na=0.01; Na = 0.03 and Na = 0.05 can be seen that the Na flakes wrap around the NMC532 granules. The Na flakes surrounding the NMC532 grains at Na = 0.01 were more abundant than the Na flakes surrounding the NMC532 at Na = 0.03.

The origin of the aggressive degradation of Ni-rich transition metal oxide cathodes for high-energy density lithium-ion batteries

Ni-rich transition metal oxide cathodes (Ni-rich NMC), which can be represented as the formular of LiNixCoyMn1-x-y (x ​≧ ​0.5, y ​< ​0.5), have emerged as the promising electrode material for high-energy density lithium-ion batteries. This battery type can achieve high capacities due to the high amount of Ni as it can provide a large number of electrons by two-stage redox reaction between Ni2+/Ni3+ and Ni3+/Ni4+. However, the increase of the Ni content in the NMC cathodes often results in a capacity fading and poor cycle life of the batteries because of the cathode degradation. Herein, the origin of the active involvements of the Ni element in the degradation process has been studied. The degradation of the Ni-rich NMC is likely to be triggered by NiO on the surface with the cathode-electrolyte interphase (CEI) formation, followed by the disorder in the layered structure both at surface and bulk after the initial cycle. The difference in the Ni content of the active material leads to the discrepancy of the surface environment. To gain deep insights into the aggressive deterioration of the Ni-rich NMC material, a density functional theory (DFT) simulation has been adopted for the cathodes with different Ni concentrations (Ni: 10%, 33%, 50%, 80%, and 100%). Also, the electronic structure of LiNi0.5Co0.2Mn0.3O2, and LiNi1/3Co1/3Mn1/3O2 are examined at 50% Li+ (de)intercalation. The findings deduced from the DFT study suggest that the Ni(d)-O(p) character with high oxidation Ni (Ni3+ and/or Ni4+) is the key to understand the (electro)chemical process involved with the degradation mechanism of the cathode.

Enhanced structure and electrochemical stability of single crystal nickel-rich cathode material by La2Li0.5Co0.5O4 surface coating

The emergence of single crystal nickel-rich cathode materials preparation offsets the poor cycle performance of traditional ternary cathode materials, with an efficient enhancement of the energy density. Despite all this, the stability of single crystal Ni-rich materials is still hard to fully meet the commercial requirements. We select La and Co elements for co-coating single crystal cathode materials by an efficient method, La2Li0.5Co0.5O4 coating layer with a thickness of about 5 nm is successfully formed on the single crystal nickel-rich samples. The coating layer effectively protect nickel-rich materials from the corrosion of electrolyte and retain a high Li-ion conductivity during charge/discharge processes. Besides, the part of residual lithium reacts with La and Co, forming La2Li0.5Co0.5O4 coating layer, and decorates the materials surface. Eventually, the single crystal NCM811 with 2 wt% La2Li0.5Co0.5O4 coating affords a terrific cyclic stability after 200 cycles. The capacity retention is 81.15% at 1 C with voltage range of 2.8–4.3 V, obtaining an 18% performance improvement compare with that of pristine material. Moreover, the rate performance and first charge/discharge efficiency are improved to a certain extent. The co-coating process with La and Co is a competitive approach to modify the performance of single crystal nickel-rich cathode materials and contribute to the commercial application of the NCM811 materials.