Lithiation Reaction Research Articles

Rational synthesis of high-performance Ni-rich layered oxide cathode enabled via probing solid-state lithiation evolution

Lithium (Li)-ion batteries using nickel (Ni)-rich layered oxide cathode have been pursued with interest due to high practical energy density. A fundamental understanding of the reaction pathways and structural evolution of the solid-phase synthesis of these materials is crucial for their rational design and process development for mass production. In this work, structural evolution during solid-state synthesis was traced via in situ technique, with a particular emphasis on the lithiation reaction and migration of transition metal (TM) ions. The sintering process is governed by the competitive relationship of decomposition and lithiation reactions, which can be regulated through temperature windows. Controlling the melting point of the Li sources, as well as their affinity to cathode precursors, is highly desired to maintain the layered ordering of TM ions throughout the whole synthesis process, which simplifies the manufacturing process and improves the quality of the manufactured cathode material.

Dry Pre‐Lithiation for Graphite‐Silicon Diffusion‐Dependent Electrode for All‐Solid‐State Battery

AbstractThe graphite/silicon‐based diffusion‐dependent electrodes (DDEs) are one of the promising electrode designs to realize high energy density for all‐solid‐state batteries (ASSBs) beyond conventional composite electrode design. However, the graphite/silicon‐based electrode also suffers from large initial irreversible capacity loss and capacity fade caused by significant volume change during cycling, which offsets the advantages of the DDEs in ful‐cell configuration. Herein, a new concept is presented for DDEs, dry pre‐lithiated DDEs (PL‐DDEs) by introducing Li metal powder. Since Li metal powder provides Li ions to graphite and silicon even in a dry state, the lithiation states of active materials is increased. Moreover, the residual Li within PL‐DDE further serves as an activator and a reservoir for promoting the lithiation reaction of the active materials and compensating for the active Li loss upon cycling, respectively. Based on these merits, ASSBs with PL‐DDE exhibit excellent cycling performance with higher columbic efficiency (85.2% retention with 99.6% CE at the 200th cycle) compared to bare DDE. Therefore, this dry lithiation process must be a simple but effective design concept for DDEs for high‐energy‐density ASSBs.

Chemical lithiation methodology enabled Prussian blue as a Li-rich cathode material for secondary Li-ion batteries

Prussian blue analogues (PBAs) have been attracting intense attention owing to its two-electron storage capability and considerable cost advantage, especially in Na-ion and K-ion batteries. However, things are quite different when it comes to Li-ion batteries, because lithium-containing Li4Fe(CN)6 precursor is not commercially available and thus the traditionally prepared Li-deficient FeFe(CN)6 products fail to couple with commercial graphite anode for full cells. Herein, we put forward a potential matching principle to guide the chemical pre-lithiation of FeFe(CN)6 into a Li-rich LixFeFe(CN)6 (x varies from 0 to 2) cathode. The potential matching principle was convincingly confirmed by theoretical analysis and over-lithiation experiments. Perylene-Li reagent was elaborately screened to serve as both Li+ and electron donor for controllable chemical lithiation reaction while preserving the host framework stable. Our work provided a general guiding principle and effective methodology for controllable synthesis of Prussian blue analogues in gradient lithiation depth, which could be served as a platform for in-depth, systematic and comprehensive research on the properties of PBAs materials.

Breaking the tert-Butyllithium Contact Ion Pair: A Gateway to Alternate Selectivity in Lithiation Reactions.

The effects of Lewis basic phosphoramides on the aggregate structure of t-BuLi have been investigated in detail by NMR and DFT methods. It was determined that hexamethylphosphoramide (HMPA) can shift the equilibrium of t-BuLi to include the triple ion pair (t-Bu-Li-t-Bu)-/HMPA4Li+ which serves as a reservoir for the highly reactive separated ion pair t-Bu-/HMPA4Li+. Because the Li-atom's valences are saturated in this ion pair, the Lewis acidity is significantly decreased; in turn, the basicity is maximized which allowed for the typical directing effects within oxygen heterocycles to be overridden and for remote sp3 C-H bonds to be deprotonated. Furthermore, these newly accessed lithium aggregation states were leveraged to develop a simple γ-lithiation and capture protocol of chromane heterocycles with a variety of alkyl halide electrophiles in good yields.

Architecting “Li-rich Ni-rich” core-shell layered cathodes for high-energy Li-ion batteries

Li-rich or Ni-rich layered oxides are considered ideal cathode materials for high-energy Li-ion batteries (LIBs) owing to their high capacity (> 200 mAh g–1) and low cost. However, both are suffering from severe structural instability upon high-voltage cycling (> 4.5 V). Here, “Li-rich Ni-rich” Li1.08Ni0.9Mn0.1O2 oxides with core-shell architecture are designed and synthesized to improve their high-voltage cyclability. These oxides are determined to be composed of a less reactive “Li-rich Mn-rich” shell and a high-capacity “Li-rich Ni-rich” core. As Li-ions gradually enter into the core-shell precursor during high-temperature lithiation reaction, the interdiffusion of elements across the interphase between the Mn-rich shell and the Ni-rich core successively occurs. Such thermally-driven atomic interdiffusion could lead to a thickness-controllable “Li-rich Mn-rich” shell, which can guarantee an exceptional structural reversibility for the layered “Li-rich Ni-rich” core upon long-term cycling. As a consequence, the optimized core-shell Li1.08Ni0.9Mn0.1O2 achieves a capacity retention of 96% at 0.1 C after 100 cycles in the voltage range of 2.7–4.6 V. These findings might open up a new avenue for rational design of advanced cathode materials for LIBs and beyond.

Rational design of NiO/NiSe2@C heterostructure as high-performance anode for Li-ion battery

Biphasic or multiphase heterostructures have promising futures in advanced electrode materials for energy-related applications because of their desirable synergistic effects. Here we prepared a rational NiO/NiSe2@C heterostructure microsphere through carbonization, selenization, and oxidation using Ni-MOF as a precursor. Electrochemical studies were conducted to examine the Li+ storage characteristics, and density functional theory (DFT) was utilized to comprehend the underlying mechanism. When employed as the anode for LIBs, the NiO/NiSe2@C showed a high specific capacity and long-term cyclic stability, with a specific capacity of 992 mAh g−1 for 600 cycles at a current density of 0.2 A g−1. The NiO/NiSe2@C exhibits a significantly enhanced lithium-ion diffusion coefficient (DLi+) value. The DFT results show that an electron-rich area forms at the NiO/NiSe2 heterointerface, where the metalloid selenium transfers electrons to the oxygen atoms. The lithiation reactions were improved dramatically by redistributing interfacial charges, which can trigger a built-in electric field that dramatically promotes the capacitance contribution of electrode materials, enhances the lithium storage capacity, and accelerates the ion/electron transmission. The rational synthesis of NiO/NiSe2@C heterostructure can provide an idea for designing novel heterostructure anode materials.

Ceramic-in-polymer solid electrolyte reinforced by in-situ polymerization of PEGDA interlayer for lithium metal battery

The solid electrolyte -is regarded as the proprietary electrolyte to solve the safety problem of high-energy-density lithium metal batteries (LMBs). Combined with the both advantages of inorganic ceramic and polymer electrolytes, the ceramic-in-polymer solid electrolyte of 15 wt% Li0.33La0.557TiO3-in-poly(vinylidene fluoride-co-hexafiuoropropylene) (LLTO-in-P(VdF-HFP)) is proposed. Since the severe lithiation reaction between LLTO ceramic and lithium metal anode, in situ polymerization of degradable poly(ethylene glycol) diacrylate (PEGDA) as protective layer on the surface lithium metal is constructed, which not only effectively avoids the side reaction, but also suppresses the growth of lithium dendrites. Under the premise of ensuring the safety of solid state LMBs, trace liquid electrolyte is added into the electrolyte/electrode interface to reduce solid-solid interfacial resistance. The unique design of solid electrolyte combined with protective lithium anode is beneficial to the stable cycling of Li||Li symmetric cells for more than 700 h under current density of 0.2 mA cm−2, compared with only 200 h cycling life for the same electrolyte using the bare lithium anode. The assembled Li||LiNi0.6Co0.2Mn0.2O2 full-cell exhibits a specific discharge capacity of 176 mAh g−1 at 0.2C rate between 3.0 and 4.35 V, maintaining 90.6% of initial capacity after 200 cycles. Therefore, the developed solid electrolyte with unique protected lithium anode exhibits potential application in high-energy-density solid LMBs.

Synthesis of single-crystal LiNi0.8Co0.1Mn0.1O2 materials for Li-ion batteries by microfluidic technology

Single-crystal LiNixMnyCo1-x-yO2 (SC-NMC) cathode with electro-chemo-mechanically compliant microstructure is regarded as a promising candidate for high-energy–density lithium ion battery. However, the research of Ni-rich SC-NCM still lags behind its corresponding polycrystalline cathode materials, mainly due to the difficulties in synthesis. Herein, the single-crystal LiNi0.8Mn0.1Co0.1O2 cathode (SC-NCM811) was successfully synthesized by microfluidic technology combined with the solid-state lithiation process. The nano-sized Ni0.8Co0.1Mn0.1(OH)2 precursor prepared via microfluidic technology enhances its accessibility to lithium salts, thus exhibiting high chemical activity for lithiation reaction. As a result, the optimized SC-NCM811 cathode shows relatively small-scale grain size (<3 μm), low cation mixing and well layered structure, which is beneficial to electrochemical kinetics and redox reversibility. The electrochemical characterization results further reveal that the optimized SC-NCM811 cathode can well balance the cycle performance and rate capability, showing good electrochemical performance. Overall, microfluidic technology is expected to provide a new strategy for preparing single-crystal Ni-rich cathode materials, which may extend to the commercial application of other cathode materials.

Redox Promotion by Prelithiation Modification of the Separator in Lithium–Sulfur Batteries

The sluggish “liquid–solid” kinetics between lithium polysulfide (Li2Sx (x ≤ 4)) and lithium sulfide (Li2S) impedes the electrochemical performance of lithium–sulfur batteries (LSBs). The prelithiation modification of the separator has been proven to promote the reduction of Li2Sx (x ≤ 4), but its mechanism and effect on Li2S-oxidation are still unclear. In this work, three kinds of lithiated metformin [LixMF (x = 0.8, 1.0, 2.0)] were prepared via the lithiation reaction using MF as the precursor. Combining experiments and theoretical calculations, we find that the bidentate coordination bond of Li1(Li1–N1&Li1–N2) in Li1.0MF can be reinforced at charging potentials, which triggers the weakening of the Li–S bond in Li2S, thereby promoting Li2S-oxidation. In contrast, both the Li1′ bidentate coordination bond (Li1′–N1&Li1′–N2) and Li2–N3 bond in Li2.0MF shift the electron cloud between the two Li–S bonds in Li2S but fail to weaken the Li–S bond or facilitate Li2S-oxidation. After LixMF (x = 0.8, 1.0, 2.0) was introduced into the cathode side of the polypropylene (PP) separator, Li1.0MF delivers the excellent cycling stability with the high sulfur loading and lean electrolyte. In other words, the modification of the PP separator needs to be moderately prelithiated, rather than maximumly prelithiated.

Investigation of silicon nanoparticle size on specific capacity of Li-ion battery via electrochemical impedance spectroscopy

Silicon is an attractive anode material in Li-ion batteries due to its high specific capacity, but the stability of silicon limits its industrial-scale application. To avoid this, the particle size reduction below 150 nm (critical radius) showed improved reactivity and cycle life but still below the benchmark for industrial-scale application. In this work, we applied the impedance analysis to understand the physicochemical processes occurring at the anode (Si electrode)/electrolyte interface. For this, we fabricated three samples of Si anode with 50 nm, 150 nm, and a mixture of 50 and 150 nm particles in equal ratios. The small particle size sample showed low charge transfer resistance, showing the highest activity towards lithiation and delithiation reaction, but high SEI formation hampers the overall capacity of the device. On the other hand, the 150 nm sample showed the low SEI formation but high charge transfer resistance due to low surface area. Finally, the mixed sample showed the compromise between the charge transfer reaction and SEI formation showing the lowest polarisation resistance after 50 cycles. Thus, the mixed sample having the advantage of intermediate surface area and intermediate SEI formation gives the highest capacity.

First-principles assessment of chemical lithiation of sulfide solid electrolytes and its impact on their transport, electronic and mechanical properties

Sulfide-based solid electrolytes (SEs) have received considerable attention, but their practical application is hindered by the lack of chemical stability. When in contact with Li metal, sulfide SEs may undergo decomposition induced by lithiation, which could be largely responsible for the high interfacial impedance observed between them. While the underlying mechanism is still uncertain, this first-principles study examines the structural and compositional evolution of sulfide materials, Li3PS4 and Li10GeP2S12, associated with chemical lithiation and its impact on their transport, electronic and mechanical properties. Our calculations demonstrate that the lithiation reaction is thermodynamically favorable until reaching full lithiation in which PS43− and GeS44− tetrahedral anions are completely decomposed to S2−, P3- and Ge4− atomic ions. This process is also found to involve the transition formation of small P(Ge) clusters and more importantly an increase in the relative density which may cause void formation and thus structural failure near the Li metal/SE interface. Moreover, our analyses highlight that, even when fully lithiated, the sulfide materials could retain the high Li-ion conductivity as well as the ability to block electron transport. This suggests that the chemical decomposition of sulfide SEs would not be the only factor that is responsible for the increase of interfacial impedance during electrochemical cycling.

Manipulation of π-aromatic conjugation in two-dimensional Sn-organic materials for efficient lithium storage

Sn-based materials are promising candidates for lithium storage but suffer generally from huge volume change during the (de)lithiation processes. Sn-organic materials with monodispersed Sn centers surrounded by lithium active ligands can alleviate the volume change of anode materials based on reversible (de)lithiation processes. However, the structural factors governing the kinetics of lithium storage and utilization efficiency of active sites are not well understood to date. Herein, we report three two-dimensional Sn-organic materials with enhanced lithium storage performance by manipulation of π-aromatic conjugation of the ligands. The increasing π-aromatic conjugation plays a key role in promoting efficient lithium storage, and the volume expansion during the (de)lithiation reaction is suppressed in these Sn-organic materials. This work reveals that the π-aromatic conjugation of the ligand is crucial for improving the kinetics of lithium storage and the utilization of active sites in metal-organic materials with minimised volume expansion.

Durable Li2CN2 Solid Electrolyte Interphase Wired by Carbon Nanodomains via In Situ Interface Lithiation to Enable Long‐Cycling Li Metal Batteries

AbstractLithium metal batteries (LMBs) are becoming the promising candidate of high‐energy storage systems. However, the fragile natural solid electrolyte interphase (SEI) cannot retard the Li dendrite growth at anode, which will cause the low coulombic efficiency (CE) of Li plating/stripping and safety hazards in LMBs. Here, an in situ construction strategy of novel artificial SEI consisting of Li2CN2 ionic conductor wired by carbon nanodomains via dicyandiamide solution reaction method on Li metal surface is proposed. This lithiophilic Li2CN2 has the higher anti‐reduction stability and longer critical length for Li dendrite, showing the excellent dendrite suppressing ability. The wired carbon domains promote the electron connection and charge homogenization in SEI, leading to the uniform Li nucleation around Li2CN2/C grains with enhanced interface kinetics and reduced polarization. This dual conductive Li2CN2/C network enables the durable preservation of high CE and low voltage hysteresis during Li plating/stripping, endowing LiNi0.8Mn0.1Co0.1O2/Li cells with ultralong cycling life exceeding 1000 cycles at high rate. The cycling stabilization effect is also remarkable even under thin Li anode and high‐loading cathode conditions. This study provides a solution to robust SEI configuration of high conductivity via in situ interface lithiation reaction for high‐performance LMBs.

Sulfur/Polyacrylonitrile-Based N-Terminated Graphene Nanoribbon Cathodes for Li-S Batteries

Conductive sulfur/carbon copolymers with a high reversible capacity are promising alternative cathode materials for lithium-sulfur batteries. Here, the focus is set on nitrogen-terminated zigzag graphene nanoribbons (N-GNRs) resembling intermediate product of electrospun polyacrylonitrile (PAN)-based carbon nanofibers. In particular, the possibility of combining strong nitrogen-sulfur interactions, which has been recently shown to lead to a shuttle-free discharge mechanism, and superior electrical conductivity of graphene nanoribbons is explored in S/N-GNR copolymers. Structural and electronic properties of ${\mathrm{S}}_{x}/$N-GNR structures, $x=1,\dots{},8$, prior and during the discharge are studied using density-functional theory calculations along with ab initio molecular dynamics simulations. It is found that the GNR backbone assumes a rippled structures in all S/N-GNR structures considered here. The most favorable sulfur structures in S/N-GNR copolymers are found to consist of short sulfur chains with $x\ensuremath{\sim}4,5$. It is also observed that, similar to N-GNRs, S/N-GNR copolymers show a metallic behavior which is brought about by the conductive backbone. In addition, consecutive lithiation reactions are studied and product structures are obtained. It is demonstrated that a shuttle-free, solid-solid transformation could also be expected during the discharge of S/N-GNR copolymers, whereas the lithiated structures remain electrically conductive, irrespective of the discharge state. Therefore, the current study promotes the use of S/N-GNR copolymers as an alternative to other poorly conductive PAN-based S/C copolymer cathodes for lithium-sulfur batteries (such as S/cPAN), while largely mitigating lithium polysulfide formation.

Stabilizing surface chemistry and texture of single-crystal Ni-rich cathodes for Li-ion batteries

The single-crystalline Ni-rich cathodes are believed to help improve the safety of Li-ion batteries (LIBs), however, the ion-diffusion limits their high-rate performance owing to large single-crystal particles. Herein, a dual-modification strategy of surface Li 2 TiO 3 -coating and bulk Ti-doping has been performed to achieve high-rate single crystal LiNi 0.83 Co 0.12 Mn 0.05 O 2 (NCM) cathode. The Li-ion conductive Li 2 TiO 3 coating layer facilitates the Li-ion transfer and prevents the electrolyte erosion. Meanwhile, the robust Ti-O bonds stabilize the cubic close-packed oxygen framework and mitigate the Li/Ni disorder. The synergy endows the dual-modified NCM with enhanced de-/lithiation reaction kinetics and stable surface chemistry. A high specific capacity of 128 mAh g -1 is delivered even at 10 C with an extended cycle life. This finding is reckoned to pave the way for developing high energy density LIBs for long-range electric vehicles.

Revealing the complex lithiation pathways and kinetics of core-shell NiO@CuO electrode

• Three-dimensional core-shell NiO@CuO electrode via simple phase separation strategy. • The NiO@CuO exhibits superior rate and stability performance. • The reaction kinetics and lithium pathways of the NiO@CuO electrode are revealed. • The chemomechanical simulation discloses the mechanical kinetics during lithium storage. Nanostructured composite electrodes with multiple active phases offer extraordinary performance that can be harnessed in future batteries. However, it is difficult to disclose the complicated reaction pathways. In this work, NiO@CuO core-shell nanocomposites are prepared and used as anodes for lithium-ion batteries, with superior rate and stability performance compared with single-phase CuO and NiO. Using a combination of in situ and ex situ electron microscopy, a two-stage lithiation reaction pathway on NiO@CuO is identified, with CuO reduced to Cu 2 O first and followed by the simultaneous reduction of both Cu 2 O and NiO to metals, resolving the existing inconsistency in literature. Chemomechanical simulation further discloses the key role of the core-shell structure in high cycling stability of NiO@CuO, which decreases the probability of cracking during the discharge-charge process. This work provides new insights to explore lithiation mechanisms and kinetics in novel electrodes, which contribute to further development of various electrode materials. Three-dimensional core-shell structured NiO@CuO nanoparticles deliver high lithium storage performance. By incorporating advanced electron microscopic analysis with chemomechanical simulation, complex lithiation reaction pathways, the reaction kinetics and capacity contributions for different species are fully revealed.

Double-phase 1T/2H–MoS2 heterostructure loaded in N-doped carbon/CNT complex carbon for efficient and rapid lithium storage

MoS2 has been considered as a potential anode for lithium-ion batteries. Most of the lab-prepared MoS2 anode materials are 2H phase with low intrinsic conductivity. To compensate the intrinsic low conductivity of 2H–MoS2 and its structural instability in cycles, a N-doped carbon-carbon nanotube (NC-CNT) carbon complex is prepared as the basic structure for MoS2 growth, and a 1T/2H–MoS2 heterostructure is fabricated on this structure. On one hand, CNTs create additional pores and connect isolated sheets of the NC, which provides enough inner growth space for MoS2 and maintains the overall electrical conductivity. On the other hand, the double-phase 1T/2H–MoS2 with high content (60%) of the metallic 1T-MoS2 gives a larger layer spacing, higher internal electron conductivity, and more active lithiation and de-lithiation reactions. To serve as anode for lithium-ion batteries, the synthesized 1T/2H–MoS2@NC–CNT has a reversible capacity of 764.99 mAh g−1 at 200 mA g−1 and an high-rate capacity of 547.7 mAh g−1 at 1000 mA g−1 even after 1000 cycles. By studying the reaction kinetics, impedance and lithiation/delithiation mechanism during electrochemical reactions, it is concluded that 1T/2H–MoS2@NC–CNT obtains declined charge transfer resistance, accelerated diffusion of Li+, improved cyclic stability, and enhanced structure/property reversibility from the carbon complex and the high-content 1T phase MoS2.

Electrochemical Performance of Electrophoretically Deposited Nickel/ Cobalt Antimony Oxide-Carbon Black Negative Electrodes for Alkali-Ion Batteries

In recent years, the requirement for portable power has increased due to the miniaturization of electronic devices. Developing rechargeable lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), with high power and energy density, long cycle life is the need of the hour. In this present work, nickel antimony oxide (NiSb2O6; NSO) and cobalt antimony oxide (CoSb2O6; CSO), two relatively new conversion-type anode materials have been explored as negative electrodes for both LIB and SIB. Conversion-type anode materials offer many advantages like ease of synthesis, requires inexpensive and abundantly available precursors and exhibit high specific capacities. Besides, relatively higher redox potentials of such anodes minimize the chance of lithium dendrites formation. A simple co-precipitation followed by calcination at 1000◦C leads to formation of tri-rutile phase NSO and CSO powder. The microstructural analysis using scanning electron microscopy of NSO and CSO powder confirms the formation of asymmetric particles having size in the range of 50-100nm. FTIR and Raman results of the calcined NSO and CSO powder indicate the presence of Sb2O6 2- units along with Ni+2/Co+2. The NSO-CB and CSO-CB electrodes are fabricated by facile and reproducible electrophoretic deposition (EPD) technique. EPD is a facile colloidal technique which can be adopted to fabricate different types of materials like conversion, insertion and alloying anode on any complex shaped substrate. Besides being an economical and ecofriendly process, EPD offers excellent reproducibility and control over the deposited film thickness. At a deposition parameter of 100V for 3minutes, well-adhered and uniform coating of NSO-CB and CSO-CB are obtained on the copper current collector. The SEM micrographs of the EPD grown electrodes substantiate the formation of a porous film with uniform distribution of active materials and carbon black (CB). Detailed ex-situ XRD analysis has been carried out to find out the lithium storage mechanism of NiSb2O6 material. It is observed that the NiSb2O6 breaks into NiO and Sb2O5 in the first lithiation step. These oxides further participate in reversible lithiation and de-lithiation reactions in the subsequent cycles. When used as a lithium-ion anode, the NSO-CB and CSO-CB electrode deliver a stable reversible capacity of 594mAhg-1 and 612mAhg-1, respectively, at a specific current of 0.5Ag-1 after 100 cycles (Fig 1(a)). Both the anode material exhibits excellent rate performance delivering a specific capacity of 397mAhg-1 and 510mAhg-1, respectively, at a high specific current of 4Ag-1. On the other hand, as a sodium-ion anode, the NSO-CB and CSO-CB electrodes are able deliver a stable reversible capacity of 255mAhg-1 and 150mAhg-1, respectively, at a specific current of 0.1Ag-1 after 50 cycles (shown in Fig 1(b)). Cyclic voltametric study at different scan rates reveals that the electrochemical reactions of NSO and CSO are mainly dominated by diffusion-controlled behavior. Therefore, both NSO and CSO can be a potential anode material for alkali-ion batteries.Fig 1: Cyclability performance of NSO-CB and CSO-CB electrodes as (a) lithium-ion battery anode, cycled at 0.5mAg-1 specific current and (b) sodium-ion battery anode, cycled at 0.1mAg-1 specific current in the voltage range of 0.01-2.5V. Figure 1

Study on lithium storage performance of plum-putting-like CoP nanoparticles embedded in N, P co-doped porous carbon

Metallic cobalt phosphide (CoP) has a higher theoretical capacity than traditional graphite anode due to its unique lithium storage mechanism. However, CoP can not be directly used as anode material because of its insufficient conductivity and serious volume expansion in cycles. Here, CoP was modified by nanocrystallization and carbon compositing methods, and plum-putting-like CoP nanoparticles embedded in nitrogen and phosphorus co-doped porous carbon (CoP@NPPC) were prepared. The successful nanocrystallization strategy leads to the formation of tiny CoP nanodots smaller than 20 nm and nanoparticles smaller than 100 nm, which uniformly disperse in the simultaneously formed N and P co-doped porous carbon. The CoP nanodots and nanoparticles are chemically bonded to carbon by PC bond, which is theoretically proved to bring increased density of states of CoP at Fermi level, responsible for its conductivity improvement. At the same time, the nanocrystallization of CoP also alleviates its volume expansion and particle breakage after numbers of lithiation reactions, thus improving the electrode stability in cycles. Based on the above characteristics, CoP@NPPC achieves a high capacity retention rate of 95.9% and a remaining specific capacity of 380.1 mAh g−1 after 1800 cycles at the current density of 5 A g−1. Moreover, the preparation of CoP@NPPC is achieved by a simple carbothermic treatment using a highly safe flame-retardant material as both P and C sources, which avoids the release of highly toxic phosphine that are usually involved in traditional phosphorization methods.

Solid-State Lithiation Reaction: What Is the Actual Lithiation Temperature?

Solid-State Lithiation Reaction: What Is the Actual Lithiation Temperature?