Cooperative structure of Li/Ni mixing and stacking faults for achieving high-capacity Co-free Li-rich oxides

Co-free Li-rich layered oxides(LLOs)are emerging as promising cathode materials for Li-ion batteries due to their low cost and high capacity.However,they commonly face severe structural instability and poor electrochemical activity,leading to diminished capacity and voltage performance.Herein,we introduce a Co-free LLO,Li_(1.167)Ni_(0.222)Mn_(0.611)O_(2)(Cf-L1),which features a cooperative structure of Li/Ni mixing and stacking faults.This structure regulates the crystal and electronic structures,resulting in a higher discharge capacity of 300.6 mA h g^(-1)and enhanced rate capability compared to the typical Co-free LLO,Li_(1.2)Ni_(0.2)Mn_(0.6)O_(2)(Cf-Ls).Density functional theory(DFT)indicates that Li/Ni mixing in LLOs leads to increased Li-O-Li configurations and higher anionic redox activities,while stacking faults further optimize the electronic interactions of transition metal(TM)3d and non-bonding O 2p orbitals.Moreover,stacking faults accommodate lattice strain,improving electrochemical reversibility during charge/discharge cycles,as demonstrated by the in situ XRD of Cf-L1 showing less lattice evolution than Cf-Ls.This study offers a structured approach to developing Co-free LLOs with enhanced capacity,voltage,rate capability,and cyclability,significantly impacting the advancement of the next-generation Li-ion batteries.

Oxygen-defects evolution to stimulate continuous capacity increase in Co-free Li-rich layered oxides

Though oxygen defects are associated with deteriorated structures and aggravated cycling performance in traditional layered cathodes,the role of oxygen defects is still ambiguous in Li-rich layered oxides due to the involvement of oxygen redox.Herein,a Co-free Li-rich layered oxide Li_(1.286)Ni_(0.071)Mn_(0.643)O_(2)has been prepared by a co-precipitation method to systematically investigate the undefined effects of the oxygen defects.A significant O_(2)release and the propagation of oxygen vacancies were detected by operando differential electrochemical mass spectroscopy(DEMS)and electron energy loss spectroscopy(EELS),respectively.Scanning transmission electron microscopy-high angle annular dark field(STEMHAADF)reveals the oxygen vacancies fusing to nanovoids and monitors a stepwise electrochemical activation process of the large Li_(2)MnO_(3)domain upon cycling.Combined with the quantitative analysis conducted by the energy dispersive spectrometer(EDS),existed nano-scale oxygen defects actually expose more surface to the electrolyte for facilitating the electrochemical activation and subsequently increasing available capacity.Overall,this work persuasively elucidates the function of oxygen defects on oxygen redox in Co-free Li-rich layered oxides.

Synthesis and electrochemical performance of La_(2)CuO_(4)as a promising coating material for high voltage Li-rich layered oxide cathodes

The structural transformations,oxygen releasing and side reactions with electrolytes on the surface are considered as the main causes of the performance degradation of Li-rich layered oxides(LROs)cathodes in Li-ion batteries.Thus,stabilizing the surfaces of LROs is the key to realize their practical application in high energy density Li-ion batteries.Surface coating is regarded as one of the most effective strategies for high voltage cathodes.The ideal coating materials should prevent cathodes from electrolyte corrosion and possess both electronic and Li-ionic conductivities simultaneously.However,commonly reported coating materials are unable to balance these functions well.Herein,a new type of coating material,La_(2)CuO_(4)was introduced to mitigate the surface issues of LROs for the first time,due to its superb electronic conductivity(26-35 mS·cm^(-1))and lithium-ionic diffusion coefficient(10^(-12)-10^(-13)cm^(2)·s^(-1)).After coating with the La_(2)CuO_(4),the capacity retention of Li_(1.2)Ni_(0.54)Co_(0.13)Mn_(0.13)O_(2)cathode was increased to 85.9%(compared to 79.3%of uncoated cathode)after 150 cycles in the voltage range of 2.0-4.8 V.In addition,only negligible degradations on the deliverable capacity and rate capability were observed.

Depolarization of Li-rich Mn-based oxide via electrochemically active Prussian blue interface providing superior rate capability

The high-rate cyclability of Li-rich Mn-based oxide(LMO)is highly limited by the electrochemical polarization resulting from the slow kinetic of the Li2MnO3 phase.Herein,the Prussian blue(PB)coating layer with specific redox potential is introduced as a functionalized interface to overcome the side effect and the escaping of O on the surface of LMO,especially its poor rate capability.In detail,the PB layer can restrict the large polarization of LMO by sharing overloaded current at a high rate due to the synchronous redox of PB and LMO.Consequently,an enhanced high rate performance with capacity retention of 87.8%over 300 cycles is obtained,which is superior to 50.5%of the pristine electrode.Such strategies on the high-rate cyclability of Li-rich Mn-based oxide compatible with good low-rate performances may attract great attention for pursuing durable performances.

Enhanced high-temperature performance of Li-rich layered oxide via surface heterophase coating

Li-rich layered oxides have become one of the most concerned cathode materials for high-energy lithiumion batteries, but they still suffer from poor cycling stability and detrimental voltage decay, especially at elevated temperature. Herein, we proposed a surface heterophase coating engineering based on amorphous/crystalline Li3 PO4 to address these issues for Li-rich layered oxides via a facile wet chemical method. The heterophase coating layer combines the advantages of physical barrier effect achieved by amorphous Li3 PO4 with facilitated Li+diffusion stemmed from crystalline Li3 PO4. Consequently, the modified Li(1.2) Ni(0.2) Mn(0.6) O2 delivers higher initial coulombic efficiency of 92% with enhanced cycling stability at 55 °C(192.9 mAh/g after 100 cycles at 1 C). More importantly, the intrinsic voltage decay has been inhibited as well, i.e. the average potential drop per cycle decreases from 5.96 mV to 2.99 mV. This surface heterophase coating engineering provides an effective strategy to enhance the high-temperature electrochemical performances of Li-rich layered oxides and guides the direction of surface modification strategies for cathode materials in the future.

LiPO_(2)F_(2) electrolyte additive for high-performance Li-rich cathode material

Li-rich layered oxide cathodes have received considerable attention because of the high operating potential and specific capacity. However, the structural instability and parasitic reactions at high potential cause severe degradation of the electrochemical performance. In our studies, the cycling stability of Li_(1.14)Ni_(0.133)Co_(0.133)Mn_(0.544)O_(2) cathode is improved with LiPO_(2)F_(2) electrolyte additive. After 500 cycles, the capacity retention is increased from 53.6% to 85% at 3 C by LiPO_(2)F_(2) modification. This performance is mainly attributed to the enhanced interfacial stability of the Li-rich cathode. Based on systematic characterization, LiPO_(2)F_(2) additive was found to promote a stable interface film on the cathode surface during the cycling and mitigates the interfacial side reactions. This study provides new insights for improving high-potential Li-rich layered oxide batteries.

Distinctive electrochemical performance of novel Fe-based Li-rich cathode material prepared by molten salt method for lithium-ion batteries

For constructing next-generation lithium-ion batteries with advanced performances,pursuit of highcapacity Li-rich cathodes has caused considerable attention.So far,the low discharge specific capacity and serious capacity fading are strangling the development of Fe-based Li-rich materials.To activate the extra-capacity of Fe-based Li-rich cathode materials,a facile molten salt method is exploited using an alkaline mixture of LiOH–LiNO3–Li2O2 in this work.The prepared Li1.09(Fe0.2Ni0.3Mn0.5)0.91O2 material yields high discharge specific capacity and good cycling stability.The discharge specific capacity shows an upward tendency at 0.1 C.After 60 cycles,a high reversible specific capacity of ~250 m Ah g-1is delivered.The redox of Fe3+/Fe4+and Mn3+/Mn4+are gradually activated during cycling.Notably,the redox reaction of Fe2+/Fe3+can be observed reversibly below 2 V,which is quite different from the material prepared by a traditional co-precipitation method.The stable morphology of fine nanoparticles(100–300 nm)is considered benefiting for the distinctive electrochemical performances of Li1.09(Fe0.2Ni0.3Mn0.5)0.91O2.This study demonstrates that molten salt method is an inexpensive and effective approach to activate the extra capacity of Fe-based Li-rich cathode material for high-performance lithium-ion batteries.

In-situ formation of Li_(0.5)Mn_(0.5)O coating layer through defect controlling for high performance Li-rich manganese-based cathode material

Li-rich layered oxide of Li_(1.2)Mn_(0.6)Ni_(0.2)O_(2)(LMNO)with a considerable specific capacity and higher voltage is regarded as a kind of promising cathode material.However,it suffers from transition metal ion dissolution and oxygen escape that leads to rapid capacity decay.In addition,the poor lithium-ion diffusion kinetics gives rise to unsatisfied rate performance.Herein,a stable layer of Li_(0.5)Mn_(0.5)O(LMO)out of LMNO is in-situ constructed through acetic passivation and following calcination process.The generated defect structure in the composite material exhibits fast ion diffusion kinetics and the produced LMO layer can stabilize the substructure,resulting in elevated cycling stability and rate performance.In specific,the LMNO@LMO material exhibits a high initial coulombic efficiency of 80.3%and remarkable capacity retention of 80.7%after 200 cycles at 1 C.Besides,the composite material reveals prominent rate performance that delivers discharge capacities of 158 and 131 m Ah g^(-1) at 5 and 10 C,respectively.At last,this study presents a new approach to optimizing the Li-rich cathode materials.

Understanding Li roles in chemical reversibility of O2-type Li-rich layered cathode materials

Traditional O3-type Li-rich layered materials are attractive with ultra-high specific capacities,but suffering from inherent problems of voltage hysteresis and poor cycle performance.As an alternative,O2-type materials show the potential to improve the oxygen redox reversibility and structural stability.However,their structure-performance relationship is still unclear.Here,we investigate the correlation between the Li component and dynamic chemical reversibility of O2-type Li-rich materials.By exploring the formation mechanism of a series of materials prepared by Na/Li exchange,we reveal that insufficient Li leads to an incomplete replacement,and the residual Na in the Li-layer would hinder the fast diffusion of Li^(+).Moreover,excessive Li induces the extraction of interlayer Li during the melting chemical reaction stage,resulting in a reduction in the valence of Mn,which leads to a severe Jahn-Teller effect.Structural detection confirms that the regulation of Li can improve the cycle stability of Li-rich materials and suppress the trend of voltage fading.The reversible phase evolution observed in in-situ X-ray diffraction confirms the excellent structural stability of the optimized material,which is conducive to capacity retention.This work highlights the significance of modulating dynamic electrochemical performance through the intrinsic structure.

Tuning redox activity through delithiation induced protective layer and Fe-O coordination for Li-rich cathode with improved voltage and cycle performance

Li-rich layered transition metal oxides are one of the most promising cathode materials for their high energy density.However,the cathodes usually suffer from severe potential dropping and capacity fading during cycling,which are associated with the surface oxygen release and accompanied by cation densification and structural collapse.Herein,an integrative approach of simultaneous constructing uniform 3d Fe-ion doping in the transition metal layer and Li-rich Li_(5)FeO_(4) shell to grab the oxygen and prevent interfacial side reactions is proposed.The introduction of Fe induces higher redox potential and stronger 3 d Fe-O_(2)p covalent bond,triggering reversible anionic redox via a reductive coupling mechanism.And the delithiated product of Li-rich Li_(5)FeO_(4) not only acts as a protective layer alleviating the side reactions but also enhances the surface kinetic property.With the benefit of promoted reversibility of oxygen redox and enhanced surface stability,the cathode exhibits high reversible capacity and superior cycle performance.Density function theory calculation indicates that the O_(2)p non-bonding state in the cathode incorporated with Fe sits at a lower energy band,resulting in higher energy storage voltage and improved oxygen stability.Consequently,the modified cathode exhibits a discharge specific capacity of 307 m A h g^(-1)(1 C=250 m A g^(-1)),coulombic efficiency of 82.09%in the initial cycle at 0.1 C and 88.34%capacity retention after 100 cycles at 1 C.The work illustrates a strategy that could simultaneously enhance oxygen redox reversibility and interface stability by constructing lattice bond coordination and delithiation induced protective layer to develop Li-rich materials with high reversible capacity and long lifespan.

Modulation of lattice oxygen boosts the electrochemical activity and stability of Co-free Li-rich cathodes

Co-free Li-rich layered oxide cathodes have drawn much attention owing to their low cost and high energy density.Nevertheless,anion oxidation of oxygen leads to oxygen peroxidation during the first charging process,which leads to co-migration of transition metal ions and oxygen vacancies,causing structural instability.In this work,we propose a pre-activation strategy driven by chemical impregnation to modulate the chemical state of surface lattice oxygen,thus regulating the structural and electrochemical properties of the cathodes.In-situ X-ray diffraction confirms that materials based on activated oxygen configuration have higher structural stability.More importantly,this novel efficient strategy endows the cathodes having a lower surface charge transfer barrier and higher Li+transfer kinetics characteristic and ameliorates its inherent issues.The optimized cathode exhibits excellent electrochemical performance:after 300 cycles,high capacity(from 238 m Ah g^(-1)to 193 m Ah g^(-1)at 1 C)and low voltage attenuation(168 mV)are obtained.Overall,this modulated surface lattice oxygen strategy improves the electrochemical activity and structural stability,providing an innovative idea to obtain high-capacity Co-free Li-rich cathodes for next-generation Li-ion batteries.

Structure and properties of Li-rich Zn-doped LiNbO_3 Crystal

The Li-rich Zn-doped LiNbO 3 (LN) crystals were grown by the Czochralski method. The structure of the crystals was measured by ultraviolet-visible absorption spectra. The results indicated that the Li-rich Zn-doped LN crystals had the same characteristics as the pure LN crystal. After Zn 2+ entered into the lattice of Li-rich Zn-doped LN crystal, it replaced Nb Li firstly. When there was no Nb Li , Zn 2+ replaced Li + then. The second harmonic generation (SHG) property of Li-rich Zn-doped LiNbO 3 crystal was measured. The results showed that the SHG conversation efficiency of Li-rich Zn-doped LiNbO 3 crystals was higher than that of Zn-doped LiNbO 3 crystals.

Vinyltrimethylsilane as a novel electrolyte additive for improving interfacial stability of Li-rich cathode working in high voltage

Boosting the interfacial stability between electrolyte and Li-rich cathode material at high operating voltage is vital important to enhance the cycling stability of Li-rich cathode materials for high-performance Li-ion batteries.In this work,vinyltrimethylsilane as a new type of organic silicon electrolyte additive is studied to address the interfacial instability of Li-rich cathode material at high operating voltage.The cells using vinyltrimethylsilane additive shows the high capacity retention of 73.9%after 300 cycles at 1 C,whereas the cells without this kind of additive only have the capacity retention of 58.9%.The improvement of stability is mainly attributed to the additive helping to form a more stable surface film for Li-rich cathode material,thus avoiding direct contact between the electrolyte and the cathode material,slowing down the dissolution of metal ions and the decomposition of the electrolyte under high operating voltage.Our findings in this work shed some light on the design of stable cycling performance of Li-rich cathode toward advanced Li-ion batteries.

Si-induced insertion of Li into SiC to form Li-rich SiC twin crystal

The energy density of Li-ion batteries is closely related to the capacity and average voltage of cathode materials.Unfortunately,current cathode materials either have low capacity or voltage,which limits the development of high-energy-density Li-ion batteries.This has given challenge to many attempts to develop new cathode materials with high capacity and voltage.In this study,we find that Li easily inserts into the(111)plane of SiC in the presence of Si,and a well-organized Li-rich SiC twin crystal is formed.Ultraviolet-visible diffuse reflectance spectra and electrochemical test results suggest that this Li-rich SiC twin crystal possesses the band gap energy of 3.5 eV and charging capacity of 1979 mAh/g at the current density of 200 mA/g,making it a promising candidate for the cathode material in high-capacity Li-ion batteries.X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy results reveal that Si-induced Li insertion contributes to the changes in the surface species and structure of pristine SiC.These findings suggest that the Li-rich SiC twin crystal raises new possibilities for the development of high-capacity cathode materials and merits further investigation to expand its application scope.

A double-layer covered architecture with spinel phase induced by LiPP for Co-free Li-rich cathode with high-rate performance and long lifespan

Co-free Li-rich Mn-based layered oxides are promising candidates for next-generation lithium-ion batteries(LIBs)due to their high specific capacity,high voltage,low cost.However,their commercialization is hindered by limited cycle life and poor rate performance.Herein,an in-situ simple and low-cost strategy with a nanoscale double-layer architecture of lithium polyphosphate(LiPP)and spinel phase covered on top of the bulk layered phase,is developed for Li_(1.2)Mn_(0.6)Ni_(0.2)O_(2)(LMNO)using Li^(+)-conductor LiPP(denoted as LMNO@S-LiPP).With such a double-layer covered architecture,the half-cell of LMNO@S-LiPP delivers an extremely high capacity of 202.5 mAh·g^(−1)at 1 A·g^(−1)and retains 85.3%of the initial capacity after 300 cycles,so far,the best highrate electrochemical performance of all the previously reported LMNOs.The energy density of the full-cell assembled with commercial graphite reaches 620.9 Wh·kg^(−1)(based on total weight of active materials in cathode and anode).Mechanism studies indicate that the superior electrochemical performance of LMNO@S-LiPP is originated from such a nanoscale double-layer covered architecture,which accelerates Li-ion diffusion,restrains oxygen release,inhibits interfacial side reactions,suppresses structural degradation during cycling.Moreover,this strategy is applicable for other high-energy-density cathodes,such as LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2),Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.54)O_(2),LiCoO_(2).Hence,this work presents a simple,cost-effective,scalable strategy for the development of high-performance cathode materials.

Structural insights into lithium-deficient type Li-rich layered oxide for high-performance cathode

As one of the promising candidate cathode materials for the high-performance lithium-ion batteries,Li-rich layered oxides still suffer from a series of critical drawbacks,such as voltage decay,oxygen release,irrevers-ible migration of transition metal ions,etc.In this work,Li-deficient method has been confirmed as an effective approach to improve the overall electrochemical performances of Li-rich cathode.The optimized lithium-deficient Li-rich layered cathode exhibits splendid discharge capacity of~297 mAh/g at 0.1 C and prominent rate per-formance of-143 mAh/g at 5 C.Subsequently,neutron diffraction in combination with Raman spectroscopy is applied to explore and clarify the underlying mechanism for improved performances.It was found that the lithium-deficient induced nickel migration and oxygen vacancy play an significant role in improving electro-chemical performances,because migration of nickel into Li layer is able to expand the Li layer spacing and reduce the Li/Ni antisite,leading to facilitated diffusion of lithium ions.Moreover,the formation of oxygen vacancy is able to promote anionic redox processes and suppress the gas release,thus leading to higher capacity.The results present valuable structural insights into the influence of lithium deficiency and provide guidance for the devel-opment of Li-rich cathode materials.

富锂层状氧化物正极材料的微观结构调控及其性能研究

通过调整富锂层状氧化物正极材料的元素组成,实现对其体相结构内的类Li_(2)MnO_(3)相晶畴分散度的调控。通过结合高功率X射线衍射和球差电镜证明了Li_(1.08)Ni_(0.225)Co_(0.225)Mn_(0.450)O_(2)材料具有高度分散的类Li 2MnO_(3)相晶畴,同时原位微分电化学质谱测试证明了具有高度分散的类Li_(2)MnO_(3)相晶畴的富锂层状氧化物正极材料可以成功抑制晶格氧的释放。电化学测试表明:微观结构的调控虽然可以提高材料的首次库伦效率和平均放电电压,但同时也降低了晶格氧的活性,减少了放电比容量。在循环过程中晶格氧稳定性的提高减轻了结构的退化程度,富锂层状氧化物正极材料表现出更优异的循环稳定性和更缓慢的电压衰减。此外,晶格氧稳定性的提高还改善了材料的热稳定性。

通过Mo掺杂诱导低Li/Ni混排程度增强Li_(1.2)Ni_(0.13)Fe_(0.13)Mn_(0.54)O_(2)可逆容量与循环稳定性

富锂层状氧化物因能量密度高和成本低,有望成为下一代锂离子电池正极的重要候选材料.然而,富锂正极材料中阴离子氧化还原反应使晶格氧不稳定,导致电压衰减和不可逆容量损失.尽管铁代无钴富锂材料可以实现较少的电压衰减,但存在严重的阳离子混排和较差的动力学.采用一种简单易行的高价离子掺杂策略,在Li_(1.2)Ni_(0.13)Fe_(0.13)Mn_(0.54)O_(2)(LNFMO)中掺入Mo元素,拓宽了锂层间距,为Li^(+)的传输提供了更宽的通道,改善了Li^(+)的扩散动力学,有效抑制了阳离子混排,进一步稳定了层状结构.得益于此,Mo掺杂后的富锂材料表现出显著增强的电化学性能,在0.2 C电流密度下表现出209.48 mAh/g的初始放电比容量.1C下的初始放电比容量从137.02 mAh/g提高到165.15 mAh/g;循环300次后,仍有117.49 mAh/g的放电比容量,电压衰减由2.09 mV/cycle降低为1.66 mV/cycle.本文对Mo掺杂后的正极材料进行了系统表征并揭示了循环稳定的机理,为高性能富锂正极材料的设计提供了重要参考.

钙钛矿结构Li_(0.33)La_(0.557)Ti_(0.7)Cr_(0.3)O_(3)包覆稳定富锂锰基正极

富锂锰基层状氧化物凭借超高的放电比容量和较低的价格成为了极具发展前景的锂离子电池正极材料,然而,首次库仑效率较低、容量衰减严重以及较差的倍率性能等缺点制约了其进一步的应用。选用离子-电子混合导体Li_(0.33)La_(0.557)Ti_(0.7)Cr_(0.3)O_(3)作为包覆层材料,并采用共沉淀法和高温退火法将其包覆于正极颗粒上。包覆量为2%的样品性能最佳,在0.5 C下、2.0~4.8 V电压范围内,200次循环容量保持率可以达到88.2%,相比于原始样品的62.1%有了明显的提升。

锂配比对富锂锰基正极材料电化学性能的影响

富锂锰基材料(LLMO)具有高容量和高工作电压,是理想的正极材料。本文考察不同锂配比制备出富锂锰基材料,通过电感耦合等离子体(ICP)和扫描电镜(SEM)表征样品的理化数据和形貌。利用恒流充放电测试材料的电化学性能。结果表明,RM55-1.1样品具有较大的比表面积,在0.5 C首次放电比容量为185.8 mAh/g,高于其他锂配比样品比容量。经过101次循环后,其容量保持率为88.75%。在1 C的电流密度下能够达到164.8 mAh/g,具有较好的倍率性能。同时,RM55-1.1样品具有较低的电池直流内阻(DCR)增长率。因此,适量的锂配比(Li/Me=1.05~1.15)制备出的富锂锰基正极材料具有较高的容量和良好的循环性能。