Rationally designing electrolyte additives for highly improving cyclability of LiNi_(0.5)Mn_(1.5)O_(4)/Graphite cells

High voltage is necessary for high energy lithium-ion batteries but difficult to achieve because of the highly deteriorated cyclability of the batteries.A novel strategy is developed to extend cyclability of a high voltage lithium-ion battery,LiNi_(0.5)Mn_(1.5)O_(4)/Graphite(LNMO/Graphite)cell,which emphasizes a rational design of an electrolyte additive that can effectively construct protective interphases on anode and cathode and highly eliminate the effect of hydrogen fluoride(HF).5-Trifluoromethylpyridine-trime thyl lithium borate(LTFMP-TMB),is synthesized,featuring with multi-functionalities.Its anion TFMPTMB-tends to be enriched on cathode and can be preferentially oxidized yielding TMB and radical TFMP-.Both TMB and radical TFMP can combine HF and thus eliminate the detrimental effect of HF on cathode,while the TMB dragged on cathode thus takes a preferential oxidation and constructs a protective cathode interphase.On the other hand,LTFMP-TMB is preferentially reduced on anode and constructs a protective anode interphase.Consequently,a small amount of LTFMP-TMB(0.2%)in 1.0 M LiPF6in EC/DEC/EMC(3/2/5,wt%)results in a highly improved cyclability of LNMO/Graphite cell,with the capacity retention enhanced from 52%to 80%after 150 cycles at 0.5 C between 3.5 and 4.8 V.The as-developed strategy provides a model of designing electrolyte additives for improving cyclability of high voltage batteries.

Electrolyte additive enhances the electrochemical performance of Cu for rechargeable Cu//Zn batteries

Cu-based cathodes in aqueous batteries become very attractive in view of high theoretical capacity,moderate operation voltage and rich reserves of raw materials.However,their applications are obstructed by serious side reactions.The side reaction mainly arises from the spontaneous formation of Cu_(2)O,which occupies the electrode surface and lowers the reaction reversibility.Here,Na_(2)EDTA is introduced to address these issues.Both experimental results and theoretical calculations indicate that the Na_(2)EDTA reshapes the solvation structure of Cu^(2+)and modifies the electrode/electrolyte interface.Therefore,the redox potential of Cu^(2+)/Cu_(2)O is reduced and the surface of Cu is protected from H2O,thereby inhibiting the formation of Cu_(2)O.Meanwhile,the change in the solvation structure reduces the electrostatic repulsion between Cu^(2+)and the cathode,leading to high local concentration and benefiting uniform deposition.The results shed light on the applications of rechargeable Cu-based batteries.

Highly improved cyclic stability of Ni-rich/Li batteries with succinic anhydride as electrolyte additive and underlying mechanism

Lithium-metal battery based on Ni-rich cathode provides high energy density but presents poor cyclic stability due to the unstable electrode/electrolyte interfaces on both cathode and anode.In this work,we report a new strategy to address this issue.It is found that the cyclic stability of Ni-rich/Li battery can be significantly improved by using succinic anhydride(SA) as an electrolyte additive.Specifically,the capacity retention of LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811)/Li cell is improved from 14% to 83% after 200cycles at 1 C between 3.0 and 4.35 V by applying 5% SA.The underlying mechanism of SA contribution is understood by comparing the effects of malic anhydride(MA) and citraconic anhydride(CA), both of which share a similar molecular structure to SA but show different effects.On anode side,SA can but MA and CA cannot form a protective solid electrolyte interphase(SEI) on Li anode.On cathode side,three anhydrides can suppress the formation of hydrogen fluoride from electrolyte oxidation decomposition,but SA behaves best.Typically,MA shows adverse effects on the interface stability of Li anode and NCM811 cathode,which originates from its high acidity.Though the acidity of MA can be mitigated by substituting a methyl for one H atom at its C=C bond,the substituent CA cannot compete with SA in cyclic stability improvement of the cell,because the SEI resulting from CA is not as robust as that from SA,which is related to the binding energy of the SEI components.This understanding reveals the importance of the electrolyte acidity on the Ni-rich cathode and the robustness of the SEI on Li anode,which is helpful for rationally designing new electrolyte additives to further improve the cyclic stability of high-energydensity Ni-rich/Li batteries.

Stabilizing electrode-electrolyte interface for high-performance SiO_(x) anode by dual electrolyte additive

Macro-and micro-interface instability of SiO_(x)anode caused by its dramatic volume variation during cycling will result in low Coulombic efficiency and rapid capacity degradation.In this work,an organic-inorganic composite interfacial layer rich in benzene ring groups,polyisocyanates,and LiF was obtained on SiO_(x)anode by the introduction of 4-fluorophenyl isocyanate(FPI)and fluoroethylene carbonate(FEC)co-additives in electrolyte.The SiO_(x)anode material shows a capacity retention of 69.2%after 100 cycles at a current density of 1 A g^(-1)and rate capacity of 523 m A h g^(-1)at the current density of 3A g^(-1),while the SiO_(x)anode cycling in reference electrolyte has almost no capacity.

Synergistic interphase modification with dual electrolyte additives to boost cycle stability of high nickel cathode for all-climate battery

B-containing electrolyte additives are widely used to enhance the cycle performance at low temperature and the rate capability of lithium-ion batteries by constructing an efficient cathode electrolyte interphase(CEI)to facilitate the rapid Li+migration.Nevertheless,its wide-temperature application has been limited by the instability of B-derived CEI layer at high temperature.Herein,dual electrolyte additives,consisting of lithium tetraborate(Li_(2)TB)and 2,4-difluorobiphenyl(FBP),are proposed to boost the widetemperature performances of LiNi_(0.6)Co_(0.2)Mn_(0.2)O_(2)(NCM)cathode.Theoretical calculation and electrochemical performances analyses indicate that Li_(2)TB and FBP undergo successive decomposition to form a unique dual-layer CEI.FBP acts as a synergistic filming additive to Li_(2)TB,enhancing the hightemperature performance of NCM cathode while preserving the excellent low-temperature cycle stability and the superior rate capability conferred by Li_(2)TB additive.Therefore,the capacity retention of NCM‖Li cells using optimal FBP-Li_(2)TB dual electrolyte additives increases to 100%after 200 cycles at-10℃,99%after 200 cycles at 25℃,and 83%after 100 cycles at 55℃,respectively,much superior to that of base electrolyte(63%/69%/45%).More surprisingly,galvanostatic c ha rge/discharge experiments at different temperatures reveal that NCM‖Li cells using FBP-Li_(2)TB additives can operate at temperatures ranging from-40℃to 60℃.This synergistic interphase modification utilizing dual electrolyte additives to construct a unique dual-layer CEI adaptive to a wide temperature range,provides valuable insights to the practical applications of NCM cathodes for all-climate batteries.

Highly reinforce the interface stability using 2-Phenyl-1H-imidazole-1-sulfonate electrolyte additive to enhance the high temperature performance of LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)/graphite batteries

This work develops 2-Phenyl-1H-imidazole-1-sulfonate(PHIS)as a multi-functional electrolyte additive for H2O/HF scavenging and film formation to improve the high temperature performance of LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)/graphite batteries.After 450 cycles at room temperature(25℃),the discharge capacity retentions of batteries with blank and PHIS-containing electrolyte are 56.03%and 94.92%respectively.After 230 cycles at high temperatures(45℃),their values are 75.30%and 88.38%respectively.The enhanced electrochemical performance of the batteries with PHIS-containing electrolyte is supported by the spectroscopic characterization and theoretical calculations.It is demonstrated that this PHIS electrolyte additive can facilitate the construction of the electrode interface films,remove the H2O/HF in the electrolyte,and improve the electrochemical performance of the batteries.This work not only develops a sulfonate-based electrolyte but also can stimulate new ideas of functional additives to improve the battery performance.

Interface Engineering via Ti_(3)C_(2)T_(x) MXene Electrolyte Additive toward Dendrite-Free Zinc Deposition

Zinc metal batteries have been considered as a promising candidate for next-generation batteries due to their high safety and low cost.However,their practical applications are severely hampered by the poor cyclability that caused by the undesired dendrite growth of metallic Zn.Herein,Ti_(3)C_(2)T_(x) MXene was first used as electrolyte additive to facilitate the uniform Zn deposition by controlling the nucleation and growth process of Zn.Such MXene additives can not only be absorbed on Zn foil to induce uniform initial Zn deposition via providing abundant zincophilic-O groups and subsequently participate in the formation of robust solid-electrolyte interface film,but also accelerate ion transportation by reducing the Zn^(2+) concentration gradient at the electrode/electrolyte interface.Consequently,MXene-containing electrolyte realizes dendrite-free Zn plating/striping with high Coulombic efficiency(99.7%)and superior reversibility(stably up to 1180 cycles).When applied in full cell,the Zn-V_(2)O_(5)cell also delivers significantly improved cycling performances.This work provides a facile yet effective method for developing reversible zinc metal batteries.

Protective electrode/electrolyte interphases for high energy lithium-ion batteries with p-toluenesulfonyl fluoride electrolyte additive

High energy density lithium-ion batteries using Ni-rich cathode(such as LiNi0.6Co0.2Mn0.2O2) suffer from severe capacity decay.P-toluenesulfonyl fluoride(pTSF) has been investigated as a novel film-forming electrolyte additive to enhance the cycling performances of graphite/LiNi0.6Co0.2Mn0.2O2 pouch cell.In comparison with the baseline electrolyte,a small dose of pTSF can significantly improve the cyclic stability of the cell.Theoretical calculations together with experimental results indicate that pTSF would be oxidized and reduced to construct protective interphase film on the surfaces of LiNi0.6Co0.2Mn0.2O2 cathode and graphite anode,respectively.These S-containing surface films derived from pTSF effectively mitigate the decomposition of electrolyte,reduce the interphasial impedance,as well as prevent the dissolution of transition metal ions from Ni-rich cathode upon cycling at high voltage.This finding is beneficial for the practical application of high energy density graphite/LiNi0.6Co0.2Mn0.2O2 cells.

Silicon micropillar electrodes of lithiumion batteries used for characterizing electrolyte additives

The 100 crystal-oriented silicon micropillar array platforms were prepared by microfabrication processes for the purpose of electrolyte additive identification. The silicon micropillar array platform was used for the study of fluorinated vinyl carbonate(FEC), vinyl ethylene carbonate(VEC), ethylene sulfite(ES), and vinyl carbonate(VC) electrolyte additives in the LiPF_6 dissolved in a mixture of ethylene carbonate and diethyl carbonate electrolyte system using charge/discharge cycles, electrochemical impedance spectroscopy, cyclic voltammetry, scanning electron microscopy, and x-ray photoelectron spectroscopy. The results show that the silicon pillar morphology displays cross-shaped expansion after lithiation/delithiation, the inorganic lithium salt keeps the silicon pillar morphology intact, and the organic lithium salt content promotes a rougher silicon pillar surface. The presence of poly-(VC) components on the surface of FEC and VC electrodes allows the silicon pillar to accommodate greater volume expansion while remaining intact. This work provides a standard, fast, and effective test method for the performance analysis of electrolyte additives and provides guidance for the development of new electrolyte additives.

Nitrogen-rich azoles as trifunctional electrolyte additives for high-performance lithium-sulfur battery

Rechargeable lithium-sulfur(Li-S)batteries are considered one of the most promising energy storage techniques owing to the high theoretical energy density.However,challenges still remain such as the shuttle effect of lithium polysulfides(LPSs)and the instability of lithium metal anode.Herein,we propose to use nitrogen-rich azoles,i.e.,triazole(Ta)and tetrazole(Tta),as trifunctional electrolyte additives for Li-S batteries.The azoles afford strong lithiophilicity for the chemisorption of LPSs.The density functional theory and experimental analysis verify the presence of Li bonds between the azoles and LPSs.The azoles can also interact with lithium salt in the electrolyte,leading to increase ionic conductivity and lithiumion transference number.Moreover,the azoles render particle-like lithium deposition on the lithium metal anode,leading to superlong cycling of a Li symmetric cell.The Li-S batteries with Ta and Tta exhibit the initial discharge capacity of 1425.5 and 1322.2 m Ah g^(-1),respectively,at 0.2 C rate,and promising cycling stability.They also enable enhanced cycling performance of a Li-organosulfide battery.

Tris(trimethylsilyl) borate as an electrolyte additive for high-voltage lithium-ion batteries using LiNi_(1/3)Mn_(1/3)Co_(1/3)O_2 cathode

The influence of tris(trimethylsilyl) borate(TMSB) as an electrolyte additive on lithium ion cells have been studied using Li/Li Co_(1/3)Ni_(1/3)Mn_(1/3)O_2 cells at a higher voltage,4.7 V versus Li/Li^+.1 wt% TMSB can dramatically reduce the capacity fading that occurs during cycling at room temperature(RT) and elevated temperature(60 °C).After 150 cycles at 1 C rate(1 C = 278 m Ah/g),the capacity retention of Li/Li Co_(1/3)Ni_(1/3)Mn_(1/3)O_2 is up to near 72% in the electrolyte with TMSB added,while it is only about 35% in the baseline electrolyte.The electrochemical behaviors,the surface chemistry and structure of Li/Li Co_(1/3)Ni_(1/3)Mn_(1/3)O_2 cathode are characterized with charge/discharge test,linear sweep voltammetry(LSV),X-ray photoelectron spectroscopy(XPS),electrochemical impedance spectroscopy(EIS),thermal gravimetric analyses(TGA),scanning electron microscope(SEM) and transmission electron microscopy(TEM).These analysis results reveal that the addition of TMSB is able to protectively modify the electrode CEI film in a manner that suppresses electrolyte decomposition and degradation of electrode surface structure,even though at both a higher voltage of 4.7 V and an elevated temperature of 60 °C.

Multi-factor principle for electrolyte additive molecule design for facilitating the development of electrolyte chemistry

When I read the paper“Electrolytes enriched by potassium perfluorinated sulfonates for lithium metal batteries”from Prof.Jianmin Ma’s group,which was published in Science Bulletin(doi.org/10.1016/j.scib.2020.09.018),I felt excited as presented a multi-factor principle for applying potassium perfluorinated sulfonates to suppress the dendrite growth and protect the cathode from the viewpoint of electrolyte additives.The effects of these additives are revealed through experimental results,molecular dynamics simulations and first-principle calculations.Specifically,it involves the influence of additives on Li^(+)solvation structure,solid electrolyte interphase(SEI),Li growth and nucleation.Following the guidance of the multi-factor principle,every part of the additive molecule should be utilized to regulate electrolytes.This multifactor principle for electrolyte additive molecule design(EAMD)offers a unique insight on understanding the electrochemical behavior of iontype electrolyte additives on both the Li metal anode and high-voltage cathode.In these regards,I would be delighted to write a highlight for this innovative work and,hopefully,it may raise more interest in the areas of electrolyte additives.

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.

Acetic acid additive in NaNO_(3)aqueous electrolyte for long-lifespan Mg-air batteries

Mg-air batteries have attracted tremendous attention as a potential next-generation power source for portable electronics and e-transportation due to their remarkable high theoretical volumetric energy density,environmental sustainability,and cost-effectiveness.However,the fast hydrogen evolution reaction(HER)in NaCl-based aqueous electrolytes impairs the performance of Mg-air batteries and leads to poor specific capacity,low energy density,and low utilization.Thus,the conventionally used NaCl solute was proposed to be replaced by NaNO_(3)and acetic acid additive as a corrosion inhibitor,therefore an electrolyte engineering for long-life time Mg-air batteries is reported.The resulting Mg-air batteries based on this optimized electrolyte demonstrate an improved discharge voltage reaching~1.8 V for initial 5 h at a current density of 0.5 mA/cm^(2) and significantly prolonged cells'operational lifetime to over 360 h,in contrast to only~17 h observed in NaCl electrolyte.X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry were employed to analyse the composition of surface film and scanning electron microscopy combined with transmission electron microscopy to clarify the morphology changes of the surface layer as a function of acetic acid addition.The thorough studies of chemical composition and morphology of corrosion products have allowed us to elucidate the working mechanism of Mg anode in this optimized electrolyte for Mg-air batteries.

Benzoselenol as an organic electrolyte additive in Li-S battery

Lithium-sulfur(Li-S)battery is one of the promising high-energy battery systems for future use.However,the shuttle effect due to the dissolved lithium polysulfides in ether electrolyte hampers its practical application.Applying electrolyte additives in Li-S battery has been widely acknowledged as an effective way to reduce the shuttle effect and improve cycling efficiency.In this work,benzoselenol(PhSeH)is used as an organic electrolyte additive in Li-S battery.It reacts with elemental sulfur to form phenyl selenosulfide,altering the redox pathway of the cathode with the regeneration of S8 at the end of charge and enabling new redox reactions with high reversibility.The Li-S coin cell with an optimized amount of PhSeH in the electrolyte delivers a high discharge capacity of 1,436 mAh·g^(−1)and a capacity retention of 92.86%in 200 cycles,and exhibits lower discharge overpotential in comparison to the cell with blank electrolyte.The Li-S pouch cell with a low electrolyte/sulfur(E/S)ratio of 4.0μL·mg^(−1)shows a discharge capacity of 1,398 mAh and excellent capacity retention for 20 cycles.

Roles of electrolyte additive in Zn chemistry

Electrolyte regulation plays its critical role in addressing the reversibility issue of metallic Zn anode towards high-performance aqueous zinc ion batteries.In view of the flourish electrolyte additive approach,the review is organized to discuss the influence of electrolyte additive on the electrolyte-Zn chemistry for the representative zinc electrolytes.Accordingly,the effects of electrolyte additives on the fundamental physicochemical properties of electrolytes,Zn surface,and Zn deposition are discussed and summarized.Based on the revealed roles of additives in interface reaction across current literature,we further provide outlook and perspective on current issues of the additive approach and potential directions.

Bifunctional fluoropyridinium-based cationic electrolyte additive for dendrite-free Li metal anode

Although lithium metal has become a promising anode material for high-energy batteries owing to its high specific capacity and the lowest reduction potential,the continuous side reactions with electrolyte as well as the safety problem caused by Li dendrite growth restrict Li anode’s practical application.Herein,we demonstrate that N-fluoropyridinium(ArF^(+))bis(trifluoromethane)sulfonimide(TFSI-)as an electrolyte additive can protect the lithium metal by both solid electrolyte interphase(SEI)protection and electrostatic repulsion mechanisms.The ArF+cations not only participate in forming F,Ncontaining SEI protective layer on Li surface,but also act as a cationic repellent during Li deposition to inhibit Li dendrite growth.As a result,the cycle performance of Li symmetric cells and Li||LiFePO_(4)full cells were significantly improved by using ArFTFSIadded electrolyte.This study provides an electrolyte additive strategy for Li anode realizing SEI protection and electrostatic repulsion simultaneously.

Beneficial impact of lithium bis(oxalato)borate as electrolyte additive for high-voltage nickel-rich lithium-battery cathodes

High-voltage nickel-rich layered cathodes possess the requisite,such as excellent discharge capacity and high energy density,to realize lithium batteries with higher energy density.However,such materials suffer from structural and interfacial instability at high voltages(>4.3 V).To reinforce the stability of these cathode materials at elevated voltages,lithium borate salts are investigated as electrolyte additives to generate a superior cathode-electrolyte interphase.Specifically,the use of lithium bis(oxalato)borate(LiBOB)leads to an enhanced cycling stability with a capacity retention of 81.7%.Importantly,almost no voltage hysteresis is detected after 200 cycles at 1C.This outstanding electrochemical performance is attributed to an enhanced structural and interfacial stability,which is attained by suppressing the generation of micro-cracks and the superficial structural degradation upon cycling.The improved stability stems from the formation of a fortified borate-containing interphase which protects the highly reactive cathode from parasitic reactions with the electrolyte.Finally,the decomposition process of LiBOB and the possible adsorption routes to the cathode surface are deduced and elucidated.

The feasibility for natural graphite to replace artificial graphite in organic electrolyte with different film-forming additives

The feasibility for natural graphite(NG)to replace artificial graphite(AG)in organic electrolytes with different additives are investigated.Although the strong film-forming additives contributes to form robust solid electrolyte interphase(SEI)film on graphite particle surface,great differences in gas evolution,lithium inventory loss and other side reactions are observed.Lithium bis(oxalato)borate(Li BOB)and fluoroethylene carbonate(FEC)are found more effective and the combination shows to be more promising.In the optimized electrolyte,natural graphite anode exhibits excellent long-term cycling capability.After 800 cycles at high temperature,the capacity retention is comparable to that using artificial graphite.The mechanisms for the capacity-fading of the full cells with AG and NG anode are investigated by ICP,SEM and polarization studies.The results shows that NG electrode consumes more active lithium due to the rough surface and larger volume expansion.The rapid capacity-fading in the initial 100 cycles is related to the instability of the SEI film aroused from large volume expansion.The systematic analysis is inspiriting for the development of high performance lithium ion batteries with reduced cost.

Synergistic combination of a Co-doped𝜎σ-MnO_(2)cathode with an electrolyte additive for a high-performance aqueous zinc-ion battery

The key challenges in aqueous zinc-manganese dioxide batteries(MnO_(2)//Zn)are their poor electrochemical kinetics and stability,which are mainly due to low conductivity and the inevitable dissolution of MnO_(2).A syn-ergistic combination of a Co-doped𝜎σ-MnO_(2)electrode(Co-MnO_(2))and a Co(CH_(3)COO)_(2)•4H_(2)O(CoAc)electrolyte additive is here developed to design a high-performance aqueous MnO_(2)//Zn battery(denoted as a Co-MnO_(2)//Zn battery with CoAc).The introduction of Co ions(Co^(3+)/Co^(2+))into the𝜎σ-MnO_(2)electrode is achieved via a facile one-step electrodeposition method.Benefitting from the synergistic coupling effect of the Co-MnO_(2)electrode and the CoAc electrolyte additive,the fabricated Co-MnO_(2)//Zn battery with CoAc shows a commendable dis-charge capacity of 313.8 mAh g^(−1)at 0.5 A g^(−1),excellent rate performance,excellent durability over 1000 cycles(∼92%capacity retention at 1.0 A g^(−1))and admirable energy density(439.3 Wh kg^(−1)),which is a significant improvement compared with an un-doped𝜎σ-MnO_(2)//Zn battery.