Li-rich Materials Research Articles

Superior Rate Capability and Cycling Stability in Partially Cation-Disordered Co-Free Li-Rich Layered Materials Enabled by an Initial Activation Process

Superior Rate Capability and Cycling Stability in Partially Cation-Disordered Co-Free Li-Rich Layered Materials Enabled by an Initial Activation Process

Kinetic Rejuvenation of Li-Rich Layered and Disordered-Rocksalt Li-Ion Battery Cathodes upon Oxygen Redox

Li-rich cathode materials (x>1 in LixTM2-xO2, TM=transition metal) with a layered structure or a disordered-rocksalt structure have received tremendous attention as advanced battery cathodes [1,2,3]. These materials can deliver substantially higher gravimetric capacity (>250 mAh/g) and energy density (>800 Wh/kg) compared to traditional materials (e.g., LiCoO2; ~170 mAh/g, 660 Wh/kg). Moreover, they improve the Li-ion batteries' sustainability by removing or greatly reducing scarce and environmentally unfriendly elements in their structure. In these materials, the theoretical TM-redox capacity is typically limited to ~140 mAh/g because of the limited amount of redox-active TMs in their crystal structure [1,2,3]. As a result, to achieve a very high capacity (> 250 mAh/g), O-redox must additionally take place in the materials, which occurs in local Li-rich environments (e.g., OLi4TM2, OLi5TM1) around oxygen where there are non-bonding O 2p orbitals [4]. In Li-rich materials containing multiple TMs, the local electroneutrality demands the TM-sites in the OLi4TM2 or OLi5TM1-unit to be occupied by high-valent TM-cations (e.g., Ti4+, Mn4+) instead of low-valent ones (e.g., Ni2+), which often results in medium-range-order (MRO) of cations in the Li-rich layered cathodes or short-range-order (SRO) in the Li-rich disordered-rocksalt cathodes [1,5]. For instance, this tendency leads to the rise of the Li2MnO3-like MRO in the layered Li- and Mn-rich cathodes, and because the non-bonding O 2p orbitals are primarily in the Li2MnO3-like domains, O-redox also takes place within the domains [1,4]. Unfortunately, the radical oxygen ion generated upon oxygen oxidation is highly mobile, and as the oxygen is covalently bonded with TMs, this increased O-mobility often accompanies TM-migration, triggering reversible or irreversible structural changes in the Li-rich materials [1]. This structural changes result in oxygen loss or unwanted phase transformation, which leads to voltage- and capacity-decay. Therefore, minimizing the structural rearrangement while using combined TM- and O-redox has been widely considered a holy grail to developing Li-rich cathodes with high capacity and stability. For instance, Bruce et al. showed that by changing the superstructure from the honeycomb to ribbon structure, one could suppress the Mn-migration upon O-redox in the layered Na-(Li, Mn)-O cathode to reduce voltage hysteresis [6]. Moreover, Li-rich disordered-rocksalt cathodes also experience structural damages upon O-oxidation; hence, its mitigation by various methods (e.g., fluorination) has been at the center of its research [3,7].In this presentation, we demonstrate that, in contrast to the prevailing opinion, the O-redox-assisted structural change can be highly beneficial to Li-rich cathodes' performance by substantially reducing the internal Li-transport resistance [8]. We synthesized highly-Li-rich Co-free layered cathodes, which possess the Li2MnO3-type medium-range-order (MRO). These materials' initial capacities are low; yet, they undergo a 'rejuvenation' (activation) upon extended cycling with substantially reduced hysteresis and increased capacity, which correlates with the MRO disruption and associated volume expansion initiated by O-redox-facilitating TM-migration. Moreover, we show that virtually the same process occurs for a disordered-rocksalt-type Li-rich cathode (Li1.2Ni1/3Ti1/3Mo2/15O2), suggesting the universality of this process.Furthermore, we use this knowledge to inform a molten-salt treatment to pre-disturb MRO, expand crystal volume before cycling, and endow a surface gradient composition for our Li-rich Co-free layered cathodes, such that the treated materials can achieve high capacity (>230 mAh/g) from the very first cycle with excellent rate capability (154 mAh/g at 2 A/g) and outstanding capacity/voltage-retention (~4 % capacity-loss; ~140 mV voltage-loss after 200 cycles at 100 mA/g; >210 mAh/g). From these results, we explain the mechanism and universality of the rejuvenation process in various charge-ordered oxides and propose guidelines for designing advanced Li-rich cathode materials with combined transition metal- and oxygen-redox activities. References M. Thackeray et al., J. Mater. Chem. 17, 3112–3125 (2007).N. Yabuuchi et al., PNAS 112, 7650–7655 (2014).J. Lee et al., Nature 556, 185–190 (2018).Seo et al., Nature Chem. 8, 692–697 (2016).H. Ji et al., Nat. Commun. 10, 592 (2019).R. House et al., Nature 577, 502–508 (2020).Z. Lun et al., Adv. Energy. Mater. 1802959 (2019).J. Lee et al., ACS Appl. Energy Mater. 3, 7931–7943 (2020).

Encouraging Voltage Stability upon Long Cycling of Li-Rich Mn-Based Cathode Materials by Ta-Mo Dual Doping.

The Li-rich and Mn-based material xLi2MnO3·(1-x)LiMO2 (M = Ni, Co, and Mn) is regarded as one of the new generations of cathode materials for Li-ion batteries due to its high energy density, low cost, and less toxicity. However, there still exist some drawbacks such as its high initial irreversible capacity, capacity/voltage fading, poor rate capability, and so forth, which seriously limit its large-scale commercial applications. In this paper, the Ta-Mo codoped Li1.2Ni0.13Co0.13Mn0.54O2 with high energy density is prepared via a coprecipitation method, followed by a solid-state reaction. The synthetic mechanism and technology, the effect of charge-discharge methods, the bulk doping and the surface structure design on the structure, morphology, and electrochemical performances of the Li1.2Ni0.13Co0.13Mn0.54O2 cathode are systematically investigated. The results show that Ta5+ and Mo6+ mainly occupy the Li site and transition-metal site, respectively. Both the appropriate Ta and Ta-Mo doping are conductive to increase the Mn3+ concentration and suppress the generation of Li/Ni mixing and the oxygen defects. The Ta-Mo codoped cathode sample can deliver 243.2 mA h·g-1 at 1 C under 2.0-4.8 V, retaining 80% capacity retention after 240 cycles, and decay 1.584 mV per cycle in 250 cycles. The capacity retention can be still maintained to 80% after 410 cycles over 2.0-4.4 V, and the average voltage fading rate is 0.714 mV per cycle in 500 cycles. Compared with the pristine, the capacity and voltage fading of Ta-Mo codoped materials are effectively suppressed, which are mainly ascribed to the fact that the highly valence Ta5+ and Mo6+ that entered into the crystal lattice are favorable for maintaining the charge balance, and the strong bond energies of Ta-O and Mo-O can help to maintain the crystal structure and relieve the corrosion from the electrolyte during the charging/discharging process.

Bonding the Terminal Isocyanate-Related Functional Group to the Surface Manganese Ions to Enhance Li-Rich Cathode's Cycling Stability.

Capacity fading of Li-rich cathodes in the cycling process is mainly caused by the irreversible side reactions at the interface of electrode and electrolyte by reason of the lack of a corrosion resistant surface. In this work, isocyanate-related functional groups (-N═C═O groups and polyamide-like groups) were tightly bonded on the surface of Li-rich oxides through a urea decomposition gas heat-treatment. The surface isocyanate functionalization inhibits the side reaction of PF5 hydrolysis to give LixPFyOz and HF species at the surface of Li-rich materials in the cycle process. As compared to the untreated Li-rich sample U0, the samples with the spinel-like layer and isocyanate functionalized surface exhibited an enhanced cycle stability. The capacity retention of the treated sample U3 reached as high as 92.6% after 100 cycles at the current density of 100 mA/g, larger than 66.8% for the untreated sample. Even at a higher current density of 1000 mA/g, sample U3 gives a capacity retention of 81.7% after 300 cycles. The findings of this work reveal the importance of surface isocyanate functionalization in restraining the surface side reactions and also suggest an effective method to design Li-rich cathode materials with better electrochemistry performance.

Optimization mechanism of Li2ZrO3-modified lithium-rich cathode material Li[Li0.2Ni0.2Mn0.6]O2 for lithium-ion batteries

To achieve lithium-ion batteries with high energy and power density, it is necessary to develop alternative high-capacity cathode materials for traditional LiCoO2 or LiFePO4, such as lithium-rich manganese-based cathode materials. However, there are still some practical problems that Li-rich materials need to be further improved, such as structure transformation issue and poor rate capability. Here, the modification of Li[Li0.2Ni0.2Mn0.6]O2 cathode material by lithium-ion conductor (Li2ZrO3) has been achieved by a sol–gel method, and the optimization mechanism is preliminarily explored. The first charge/discharge specific capacities of the modified material coated with 1 wt.% Li2ZrO3 can reach 272.1 and 196.1 mAh g− 1 at 0.5 C, which are obviously higher than those of the pristine material. The rate capability has also been improved at 2 C and 5 C. As a fast lithium-ion conductor with good chemical stability, Li2ZrO3 material can form a continuous and uniform coating layer on the surface of active particles, which can inhibit the side reaction between the electrolyte and the electrode material, effectively prevent the corrosion of cathode material by HF attack, and reduce electrode polarization at high rates, leading to the improvement of the specific capacity and the structure stability of Li-rich material.

Cycling mechanism of Li2MnO3: Li–CO2 batteries and commonality on oxygen redox in cathode materials

Summary Li2MnO3 has been considered to be a representative Li-rich compound with active debates on oxygen activities. Here, by evaluating the Mn and O states in the bulk and on the surface of Li2MnO3, we clarify that Mn(III/IV) redox dominates the reversible bulk redox in Li2MnO3, while the initial charge plateau is from surface reactions with oxygen release and carbonate decomposition. No lattice oxygen redox is involved at any electrochemical stage. The carbonate formation and decomposition indicate the catalytic property of the Li2MnO3 surface, which inspires Li-CO2/air batteries with Li2MnO3 acting as a superior electrocatalyst. The absence of lattice oxygen redox in Li2MnO3 questions the origin of the oxygen redox in Li-rich compounds, which is found to be of the same nature as that in conventional materials based on spectroscopic comparisons. These findings provide guidelines on understanding and controlling oxygen activities toward high-energy cathodes and suggest opportunities on using alkali-rich materials for catalytic reactions.

Preparation and Performance of Rod-Like Lithium-Rich Spinel Li1+x Mn2−x O 4 by the Hydrothermal Synthesis-Solid Phase Calcination Method

Spinel LiMn2O4 is of value for Li-ion batteries. However, the capacity decay due to the Jahn-teller effect still must be solved. Li-rich materials depress the Jahn-Teller effect by increasing the Li-ion content and decreasing the Mn3+ content simultaneously. In this paper, rod-like Li-rich spinel Li1+xMn2−xO4 was prepared by a hydrothermal synthesis-solid phase calcination method. The electrochemical performance test showed that the Li-rich materials had higher charge-discharge capacity and cycle performance, and the Li1.06Mn1.94O4 material had the best electrochemical performance. The specific discharge capacity reached 118 mAh/g at 0.5 °C and the capacity retentions were 95.69% and 90.72%, respectively, at 25 °C and 55 °C after 100 cycles. The discharge capacities of Li1+xMn2−xO4 were better than pure LiMn2O4 under high discharge rates.

Recent development of Li-rich manganese cathode material for Li-ion batteries

Recent development of Li-rich manganese cathode material for Li-ion batteries

Long-Term Cycle Stability Enabled by the Incorporation of Ni into Li2MnO3 Phase in the Mn-Based Li-Rich Layered Materials

Co-free Mn-based Li-rich layered materials have been attracting a lot of attention due to their high capacity via the additional oxygen redox reaction and their low cost. However, their poor capaci...

Controllable preparation of Fe-containing Li-rich cathode material Li[Li1/5Fe1/10Ni3/20Mn11/20]O2 with stable high-rate properties for Li-ion batteries

Generally, the optimization of synthesis conditions has great influence on the properties of the electrode materials for lithium-ion batteries (LIBs). Nowadays, Li-rich manganese-based cathode materials with high capacity are still suffering from low first charge/discharge capacity and poor high-rate capability. In this work, Li[Li[Formula: see text]Fe[Formula: see text]Ni[Formula: see text]Mn[Formula: see text]]O2 has been successfully synthesized by hydroxide co-precipitation method, and the effect of calcination temperature on the material characteristics and electrochemical performance has been investigated. The results show that with the increase of calcination temperature, the layered structure of Li-rich material becomes better. When the calcination temperature is 800[Formula: see text]C, the prepared material exhibits the most excellent electrochemical properties, including high first charge/discharge specific capacity of 366.6/251.9 mAh g[Formula: see text] and good high-rate capability. It is expected that the results of this study can lay a solid foundation for the subsequent research on the modification of this material.

Suppress voltage decay of lithium-rich materials by coating layers with different crystalline states

Li-rich oxides are considered as the most commercial potential cathode materials due to the high theoretical specific discharge capacity. Here, ZrO2 in different crystalline states are applied as the coating layers to enhance the electrochemical performance of hollow Li[Li0.2Mn0.54Ni0.13Co0.13]O2 materials. Meanwhile, a series of characterizations (XRD, SEM, TEM, EDX etc.) are conducted to compare the effects of ZrO2 coating layer with different crystalline states on the host material. The results elucidate that the Li-rich Mn-based material with the polycrystal ZrO2 coating layer has a slight advantage in rate performance, while the host material with the single crystal ZrO2-coating layer has a better cycling performance and effectively suppresses voltage decay with the effect of excellently inhibiting layered to spinel-like phase transition and metal dissolution during charging and discharging process.

Insight of reaction mechanism and anionic redox behavior for Li-rich and Mn-based oxide materials from local structure

Li-rich and Mn-based oxides (LRMO) have been an obvious choice of high specific energy batteries owing to their unique anion redox behavior based on the main component Li 2 MnO 3 . However, there are still electrochemical behaviors that cannot perfectly match the theoretical structure. So far, most theoretical research on LRMO has been carried out around the ideal Li 2 MnO 3 structure. Nevertheless, there are a great number of non-ideal local configurations in the pristine materials under the case of practical situations. Herein, the ubiquitous complex local structures (defect-like) in the interior of Li 2 MnO 3 particle, some of which have not been observed in the past, are directly presented through the atomic-level observation. We summarized these structures and proposed for the first time the great influence of these local structures on the electrochemical and the oxygen redox behavior of LRMO by combining observation, DFT calculation, XAS, XPS and electrochemical experiments. These micro-structures have been roughly divided into four categories by the advanced AC-STEM, including the so-called stacking faults caused by the slip of the adjacent TM layer, the local multi-Li or multi-Mn arrangement due to the combination of different stacking type along a–b plane, the expansion of the interlayer spacing, and even the distribution of polycrystalline domains, of which the second and third configurations were observed for the first time. These types of local structures dominate the electrochemical reaction of electrodes in some aspects by improving the activity of oxygen non-bonding 2p states, along with the improvement of (de)intercalation ability for Li ions in the bulk through reducing the energy barrier, and they are even one of the sources of voltage hysteresis by affecting the energy level distribution of oxygen unoccupied 2p states after delithiation. This research has perfected a more comprehensive and practical understanding of LRMO under the case of practical situations, laying a key foundation for the further modification and application of LRMO cathode materials. • The new revelation of complex local structures in the practical Li-rich and Mn-based oxides. • The decisive influence of these local structures on the electrochemical behavior of anion redox and materials. • Perfection of the theoretical system by combining DFT calculation with atomic-level observation and XAS. • A new perspective for the future modification of Li-rich and Mn-based cathode materials.

Correction: Enhanced structural stability and overall conductivity of Li-rich layered oxide materials achieved by a dual electron/lithium-conducting coating strategy for high-performance lithium-ion batteries

Correction for ‘Enhanced structural stability and overall conductivity of Li-rich layered oxide materials achieved by a dual electron/lithium-conducting coating strategy for high-performance lithium-ion batteries’ by Dan Gao et al., J. Mater. Chem. A, 2019, 7, 23964–23972, DOI: 10.1039/C9TA04551A.

Influence of Cu doping and high-pressure torsion on electrochemical performance of lithium-rich cathode material

Lithium-rich manganese based layered oxide yLi2MnO3∙(1-y)LiMO2 (M=Ni, Co and Mn) is one of the candidate materials for high-capacity cathodes in next-generation lithium-ion batteries. Ion doping with cation and introducing oxygen vacancy are regarded as two methods to change the electrochemical performance of Li-rich cathode materials. In this work, Li1.2Mn0.54Co0.13Ni0.13O2 was synthesized via one-step co-precipitation process, ion doping with low cost element Cu as well as high-pressure torsion were carried out to modify the Li-rich material. Results show that doping with Cu can slightly improve the specific discharge capacity as well as the coulombic efficiency which may be attributed to the lower cation mixing degree.

Intelligent phase-transition MnO2 single-crystal shell enabling a high-capacity Li-rich layered cathode in Li-ion batteries.

Layered, Li-rich Mn-based oxides (LLMOs) are the most promising next-generation, high-energy batteries due to their relatively high specific capacities and high voltages. However, the practical application of LLMO cathodes is limited by low initial coulombic efficiencies (CEs) and poor cycling performance. Herein, we used the reaction of KMnO4 and MnSO4 under hydrothermal conditions to grow a nano-SCMO shell on the LLMO material surface (SCMO@LLMO). The unique particle/sheet compound structure of the SCMO shell is beneficial to the electrochemical reaction. SCMO has good Li storage characteristics and excellent surface structure stability in the single-crystal phase which further improves the reversible capacity, CE, and cyclic stability of the LLMO cathode. Therefore, the optimal coated sample (feedstock: 2 M KMnO4, SCMO@LLMO-2.0) exhibits a good initial discharge capacity (238.2 mA h g−1 at 1C and 173.8 mA h g−1 at 5C), initial CE (89.6% at 1C and 86.5% at 5C), and cycling performance (capacity retention of 84.67% at 1C and 62.72% at 5C after 200 cycles). This work adopts a hydrothermal method to synthesize a nano-single crystal composite material, laying a foundation for the preparation of the SCMO@LLMO cathodes for LLMO primary battery cathodes with high electrochemical performance.

A composite surface configuration towards improving cycling stability of Li-rich layered oxide materials

Scalable 345 W h kg−1 full pouch cells with guaranteed cycling life are achieved by employing the surface-modified materials.

A review on the electrochemical reaction of Li-rich layered oxide materials

Lithium-rich layered oxide materials xLi2MnO3·(1 − x)LiMO2 (M = Mn, Co, Ni, Fe, Cr, etc.) as promising cathode candidates for high energy Li-ion batteries have been summarized in this review.

Accelerating the activation of Li2MnO3 in Li-rich high-Mn cathodes to improve its electrochemical performance.

Li-rich high-Mn oxides, xLi2MnO3·(1 - x)LiMO2 (x ≥ 0.5, M = Co, Ni, Mn…), have attracted extensive research interest due to their high specific capacity and low cost. However, slow Li2MnO3 activation and poor cycling stability have affected their electrochemical performance. Herein, to solve these problems, morphology regulation and LiAlF4 coating strategies have been synergistically applied to a Li-rich high-Mn material Li1.7Mn0.8Co0.1Ni0.1O2.7 (HM-811). This dual-strategy successfully promotes the activation process of the Li2MnO3 phase and thus improves the electrochemical performance of HM-811. Theoretical computation indicates that the LiAlF4 layer has a lower Li+ migration barrier than the HM-811 matrix, so it could boost the diffusion of Li+ ions and promote the activation of the Li2MnO3 phase. Benefiting from the morphology regulation and LiAlF4 coating, the HM-811 cathode shows a high initial charge capacity of >300 mA h g-1. In addition, the modified HM-811 could deliver superior electrochemical performance even at a low temperature of -20 °C. This work provides a new approach for developing high performance cathode materials for next-generation Li-ion batteries.

Controlled synthesis of Li1.17Ni0.21Mn0.54Co0.08O2 as a cathode material for Li ion batteries

Abstract Li-rich layered oxides Li1+xMO2 (M: Ni, Co, Mn) being a combination between Li2MnO3 and LiMO2, are considered as attractive high-capacity electrode materials for Lithium ion batteries. Here, we present the composition Li1.17Ni0.21Mn0.54Co0.08O2 with low cobalt content. The synthesis process was optimized by varying the pH of the co-precipitation step and pure phase was obtained only for pH = 11.3. The morphology of the material consists on the agglomeration of quasi-spherical particles an average particle size of 157 nm. The electrochemical properties of this electrode material were investigated, and a specific capacity of 250 mAh/g was recorded in the voltage range of 2–4.8 V. While the first charge process evidenced a potential plateau at 4.5 V corresponding to the oxygen redox activity, the subsequent electrochemical behavior is governed by Ni2+/Ni4+ and Co3+/Co4+ redox couples. When cycled for 40 charge/discharge cycles at 0.1C rate, the capacity retention is still good and remains around 85% with a coulombic efficiency of around 98%. The comparison of the obtained performances with those of existing Li-rich electrode materials show the excellent features of the studied Li-rich material for the next generation Lithium-ion batteries.

Construction of a surface heterosphere for a Li-rich manganese-based cathode with improved Li storage properties

Lithium-rich, manganese-based cathode materials with high specific capacity have become a research focus in recent years; however, the transformation to the spinel phase and the dislocations of the material lead to inferior electrochemical performances. In this work, a lanthanum heterosphere was constructed on the surface of a Li-rich manganese-based material without distinct phase interface and lattice mismatch to address these problems. Such a surface heterosphere can prevent the migration of metal ions and enhance the diffusion of Li+ and transference of electrons. By virtue of the surface heterosphere, which can also preserve the oxygen vacancies, high initial discharge/charge capacities of La-LLO (359.6/293.4 mA h g−1) can also be achieved. The La-LLO cathode also exhibits outstanding cycle performance (236.7 mA h g−1 at 0.1 A g−1 during 100 cycles) and rate capability (59.3 mA h g−1 and the capacity retention of 76.9% for 500 cycles at 5 A g−1). It has been proven that such a melting impregnation method is effective in constructing a surface heterosphere on the surface of a Li-rich manganese-based material for improving Li storage properties.