Sn Coarsening Research Articles

Thermodynamic anti-agglomeration based selenium-doped tin oxide network: Enhancing cycling stability of high-rate lithium storage

In this work, the grain line-cutting effect induced by selenium doping into SnO2 aggregation was proposed to prepare uniformly distributed SnO2/Se nanoparticles (SnO2/Se NPs) network with thermodynamic anti-agglomeration force during high-temperature sintering. These SnO2/Se NPs offers abundant active sites, reduced volume expansion and fast Li+ diffusion ability, especially the enhanced electronic conductivity due to oxygen vacancies introduced by doping. More importantly, the thermodynamic anti-agglomeration of SnO2/Se NPs effectively suppresses the Sn coarsening and Li2O/Sn phase segregation during repeated charge/discharge processes. Consequently, the SnO2/Se NPs anode delivers excellent reversible capacity of 515 mAh g−1 after 500 cycles at 1 A g−1, and the SnO2/Se NPs||LiFePO4 full cells maintains a high-rate capacity of 109 mAh g−1 at 0.3 A g−1. The SnO2/Se NPs anode is compatible with high concentration polymer electrolyte (HCPE), which shows a capacity of 520 mAh g−1 after 100 cycles at 0.2 A g−1 in solid state batteries. This study provides a new insight for improving the cyclic stability of conversion-alloying anodes, offering their promising prospects for the full batteries and solid-state batteries.

Counter-intuitive mechanical performance variation in aged low-temperature interconnections in electronic packaging

Different from the conventional aging induced continuous mechanical performance deterioration in solder joints, a counter-intuitive “decrease-increase-decrease” variation in shear strength with a peak value 12 MPa higher than the initial state was captured in aged low-temperature BGA structure Cu/Sn–58Bi/Cu solder joints. The first decrease in shear strength was dominated by the coarsening of Sn and Bi phases. The following increase in shear strength was rooted in the concurrent Bi subgrain strengthening, solid solution strengthening of Bi element in Sn-rich phase and precipitation strengthening induced by the Bi-rich phase particles. The eventual decrease in shear strength was ascribed to severely deteriorated interface between the solder matrix and intermetallic compound layer being the weaker site in the long time aged solder joint. This aging induced strengthening phenomenon is inspiring in mechanical performance optimization and reliability elevation of SnBi-based solder joints for the coming chiplet and heterogeneous integration packaging.

Mesoporous C-covered Sn/SnO2-Ni nanoalloy particles as anode materials for high-performance lithium/sodium-ion batteries

Nanoscale Sn-based alloy materials are high-performance anode materials for both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), however, the insertion and extraction of Li+/Na+ during the charging and discharging process can lead to dramatic expansion of the electrode volume as well as collapse and crushing of the structure. Therefore, we successfully synthesized a new mesoporous Sn/SnO2-Ni@C composite anode material. Mesoporous Sn/SnO2-Ni@C has excellent electrochemical properties and can reach large reversible capacities after 200 cycles at 0.2 A g−1 (LIBs: 1020.7 mAh g−1, SIBs: 342.6 mAh g−1) as well as remarkable stability after 1000 cycles at 1.0 A g−1 (LIBs: 864.6 mAh g−1, SIBs: 219.3 mAh g−1). In addition, mesoporous Sn/SnO2-Ni@C also has outstanding rate performance (LIBs: 564.6 mAh g−1 at 5.0 A g−1, SIBs: 212.5 mAh g−1 at 1.0 A g−1). In particular, the unique mesoporous structure not only provides additional transport channels for Li+/Na+ and electrons, but also enables the electrode material to be fully immersed in the electrolyte. Meanwhile, the synergistic effect between Sn/SnO2-Ni alloy can prevent shuttle effect and alleviate volume expansion, the presence of Ni can prevent the coarsening of Sn. Thus, mesoporous Sn/SnO2-Ni@C has fast kinetics and is a promising anode material for LIBs/SIBs.

A preparation strategy for highly reversible conversion reaction Tin dioxide/ Carbon anode: Simple, ultrafast and scalable

Combining nanoscale engineering and physical confinement approach to prevent aggregation is a reliable strategy to achieve fully reversible conversion reaction SnO2-based anode. However, the synthesis of such nanostructures relies on complex self-sacrificing template preparation and time-consuming thermal treatment processes, which limit the practical application of high-performance SnO2 anodes for lithium-ion batteries. Herein, we present a simple strategy for the in situ preparation of SnO2 quantum dots embedded in carbon martix using an inherently advantageous MOF template and ultrafast microwave-assisted treatment in a few seconds. (denoted as SnO2 QDs@C). The dispersed SnO2 quantum dots with precise size control (≈5 nm) in the nanostructure shorten the lithium ion transport distance and enhance the reaction kinetics. Meanwhile, the carbon matrix promotes electron transport and suppresses Sn coarsening, thus achieving a highly reversible conversion reaction. Consequently, the SnO2 QDs@C anode achieves a reversible capacity of 1337 mAh g-1 after 200 cycles at 0.2 A g-1 with a capacity retention rate of more than 80%. This preparation method can be extended to prepare other metal oxide quantum dots/ Carbon composites and is expected to be applied in a wide range of fields.

SnS@C nanoparticles anchored on graphene oxide as high-performance anode materials for lithium-ion batteries.

Tin (II) sulfide (SnS) has been regarded as an attractive anode material for lithium-ion batteries (LIBs) owing to its high theoretical capacity. However, sulfide undergoes significant volume change during lithiation/delithiation, leading to rapid capacity degradation, which severely hinders its further practical application in lithium-ion batteries. Here, we report a simple and effective method for the synthesis of SnS@C/G composites, where SnS@C nanoparticles are strongly coupled onto the graphene oxide nanosheets through dopamine-derived carbon species. In such a designed architecture, the SnS@C/G composites show various advantages including buffering the volume expansion of Sn, suppressing the coarsening of Sn, and dissolving Li2S during the cyclic lithiation/delithiation process by graphene oxide and N-doped carbon. As a result, the SnS@C/G composite exhibits outstanding rate performance as an anode material for lithium-ion batteries with a capacity of up to 434mAh g-1 at a current density of 5.0Ag-1 and excellent cycle stability with a capacity retention of 839mAh g-1 at 1.0Ag-1 after 450 cycles.

A robust solvothermal-driven solid-to-solid transition route from micron SnC2O4 to tartaric acid-capped nano-SnO2 anchored on graphene for superior lithium and sodium storage

A robust solvothermal-driven solid-to-solid transition strategy is developed to craft tartaric acid-capped ultrafine SnO2 encapsulated in graphene with outstanding lithium and sodium storage reversibility due to effectively inhibited Sn coarsening.

A facile assembly of SnO2 nanoparticles and moderately exfoliated graphite for advanced lithium-ion battery anode

High-capacity SnO2 is considered as one of the most potential anode candidates but suffers from its low coulombic efficiency, low conductivity, and large volume expansion. To solve these bottlenecks, we designed an assembly of nano-SnO2 and moderately exfoliated graphite (MEG) to form a hybrid of SnO2 and MEG coated with amorphous carbon (SnO2/MEG@C). In the liquid phase system at room temperature, the moderate exfoliation of graphite and the SnO2 embedded into the MEG interlayer were realized at the same time. Graphite expansion generates plenty of parallel lamellas, which accommodates the SnO2 nanoparticles between these lamellas and prevents their agglomeration in confined spaces. The MEG as flexible and conductive support can attach SnO2 nanoparticles tightly, which enhance the electron transfer, and also can hinder the agglomeration of SnO2. Meanwhile, the carbon coating can effectively adapt to the volume changes of SnO2 nanoparticles. Moreover, the interaction between the MEG and carbon coating can form a physical barrier that effectively hinders Sn coarsening, which maintains the rapid mutual diffusion kinetics between nano Sn/Li2O interfaces, leading to the high-efficiency conversion reaction of SnO2 in the composite and excellent reversibility and cyclicity. The SnO2/ MEG@C electrode exhibits a high capacity of 691.4 mAh g−1 after 900 cycles at 1.0 A g−1. The method in this work can guide the design and synthesis of materials with high capacity and adaptive volume expansion.

Advancing Performance and Unfolding Mechanism of Lithium and Sodium Storage in SnO2 via Precision Synthesis of Monodisperse PEG‐Ligated Nanoparticles

AbstractLow conductivity and tin coarsening issues hinder the utility of tin dioxide as anode for lithium and sodium ion batteries. To significantly advance the electrochemical performance and systematically unfold the energy storage mechanism of SnO2, monodisperse poly(ethylene glycol)‐ligated SnO2 nanoparticles are in situ crafted with star‐like poly(acrylic acid)‐block‐poly(ethylene glycol) diblock copolymers as nanoreactors and uniformly confined in layer‐by‐layer stacked graphene oxide matrix (denoted SnO2@PEG‐GO). Remarkably, SnO2@PEG‐GO nanohybrids manifest fully reversible three‐step lithiation‐delithiation reactions of SnO2 with an ultrahigh 100th discharge capacity of 1523 mAh g−1 at 100 mA g−1. Moreover, SnO2@PEG‐GO nanohybrids exhibit an ultrastable sodium storage capacity of 527 mAh g−1 after 500 cycles at 50 mA g−1, and the conversion reaction between Sn and SnO is uncovered as the primary reversible sodiation–desodiation reaction of SnO2. Notably, in addition to buffering volume expansion of SnO2 nanoparticles, the synergy between PEG and GO promotes Li+ or Na+ ion and electron transfers and inhibits Sn coarsening at micro and macro scales. This work provides a robust strategy to realizing outstanding electrochemical properties and scrutinizing fundamental mechanisms that underpin the performance of active materials via surface polymer ligation, precise size control, and uniform graphene encapsulation.

Reversible formation of metastable Sn-rich solid solution in SnO2-based anode for high-performance lithium storage

Tin dioxide (SnO2) has been considered as a promising anode for high-energy alkali-ion batteries due to its high theoretical specific capacity, but still plagued by the intrinsic issues of Sn coarsening and significant volume change during cycling. Herein, a stable Ti-SnO2 material is tactfully designed and constructed via one-step simple hydrothermal reaction for highly reversible lithium storage. Density functional theory (DFT) calculations and experimental results show that a metastable Sn-rich Sn(Ti) solid solution can be reversibly formed after multiple conversion reaction of the Ti-SnO2 and exhibits high recrystallization temperature of 509–589 K. Then, the solid solution formed by Ti atoms during the cycling leading to the enhanced inhibitory effect on the coarsening of Sn. Therefore, the Sn(Ti) solid solution can maintain a small grain size of 10 nm even after hundreds of cycles. Take an example, the Ti-SnO2 anode displays a stable long life with high Li discharge capacity of 705 mAh g−1 and 95.4% capacity retention (compared to the initial specific discharge capacity) after 700 cycles at 1 A g−1. This work provides a novel and versatile strategy to suppress the coarsening of Sn by inducing a metastable Sn-rich solid solution for all Sn-based compound anodes in alkali-ion batteries.

Synthesis of SnO2@MnO2@graphite nanosheet with high reversibility and stable structure as a high-performance anode material for lithium-ion batteries

In this study, SnO2@MnO2@graphite (SMG) anode material is prepared via a facile ball-milling approach combined with hydrothermal treatment. SnO2 and MnO2 nanoparticles are evenly dispersed on numerous sheet-like graphite. MnO2 can not only play a catalytic role for facilitating the conversion reaction of Sn/Li2O to SnO2, but also as a barrier to impede the coarsening of Sn in the composite. Meanwhile, graphite nanosheets could serve as an ideal volume expansion buffer and good electron conductor. Consequently, the SMG anode delivers superior reversible capacity of 1048.5 mAhg−1, ideal rate capability of 522.2 mAhg−1 at 5.0 A g-1 and stable long-life cyclic performance of 814.8 mAhg−1 at 1.0 A g-1 after 1000 cycles. This result indicates that the incorporation of MnO2, graphite nanosheet and SnO2 have a great potential in enhancing the performance of SnO2-based anode for battery applications.

Heterostructured multi-yolk-shell SnO2/Mn2SnO4@C nanoboxes for stable and highly efficient Li/Na storage

Rationally designed transition metal oxides-based anode materials with superior electrochemical performance are still a challenge for Li and Na ion batteries (LIBs/NIBs). Herein, we have engineered novel multi-yolk-shell nanoboxes (denoted as SnO2/Mn2SnO4@C), which comprise heterostructured SnO2/Mn2SnO4 nanoparticles as yolk and phenolic resin-derived carbon as shell. The SnO2/Mn2SnO4 heterostructure can effectively hinder the coarsening of Sn and strengthen the reversibility of conversion and alloying process. Ascribing to lattice distortion and redistribution of the charge at SnO2/Mn2SnO4 heterostructure boundaries, Li+ and Na+ can rapidly migrate to anode, which accelerate the reaction kinetics. In addition, the hollow structure and phenolic resin-derived carbon shell of the SnO2/Mn2SnO4@C nanoboxes can alleviate disintegration and agglomeration of active composites. Owing to above advantages, the SnO2/Mn2SnO4@C nanoboxes as anode materials display a decent capacity of 1293 mA h g−1 after 100 cycles at 0.2 A g−1 and a splendid cycling stability at 2 A g−1 over 549 cycles for LIBs. For NIBs, a large reversible capacity of 203 mA h g−1 after 100 cycles at 0.2 A g−1 is delivered. Besides, electrochemical performances of Li (or Na) ion full cell are investigated by using the SnO2/Mn2SnO4@C nanoboxes as the anode and LiFePO4 (or Na3V2(PO4)3) as the cathode.

Improvements in mechanical properties of Sn–Bi alloys with addition of Zn and In

In order to improve the mechanical properties after thermal aging of an Sn–45Bi–2.6Zn (SBZ) alloy, which we had proposed in a previous study, in this study, we prepared Sn–Bi–Zn–In alloys and investigated the effects of the addition of In and Zn on their microstructure and mechanical properties before and after thermal aging. We found that the addition of In suppressed the microstructural coarsening of SBZ during thermal aging and can potentially help reduce the brittleness of Sn–Bi alloys. Moreover, the addition of In had significant effect on the elongation of SBZ. We theorized that the segregation of Zn at the Sn/Bi phase boundary and the formation of a solid solution of In in the Sn phase are responsible for this result. Thus, the investigated alloys have potential for use as lead-free solder materials in the electronics industry. • The addition of Zn and In in a trace amount was effective in suppressing the microstructural coarsening of Sn–Bi alloys during thermal aging. Moreover, the addition of In had a significant effect on the elongation of the alloys. •The segregation of Zn at the Sn/Bi phase boundary and the formation of a solid solution of In in the Sn phase are responsible for the phenomenon of microstructural retention during thermal aging.

Subzero temperature promotes stable lithium storage in SnO2

It is known that low operating temperature reduces significantly the discharging capacity and cycling stability of lithium ion battery (LIB). In addition LIBs are unable to charge at subzero temperatures because of the propensity for Li dendrite formation on graphite anodes. The present work we found that SnO2 anode can deliver high capacity under subzero temperature, 71% of its 30°C capacity at –20°C in a commercial LiPF6-EC/PC based electrolyte, which is much higher than that of intercalating graphite and Li4Ti5O12, alloying Si-C anodes and other materials. Most surprisingly, different from the serious capacity attenuation of electrodes occurring at room temperature, subzero temperatures effectively promotes the good cycling stability of pure SnO2 anodes toward Li storage. High capacities of 603.1 mAh g–1 at –20°C and 423.8 mAh g–1 at –30°C can be maintained stable throughout the cycles. In-situ X-ray diffraction monitoring reveals that subzero temperature suppresses Sn coarsening in lithiated SnO2 anodes to maintain a high reversibility for alloying and conversion reactions, which ensures stable capacities in 0-1.0 V and 1.0-2.4 V potential range. Furthermore, allotropy transformation from β-Sn to α-Sn could be helpful to build faster transfer channels for Li-ions during de-/lithiation in subzero temperatures. This work shows that SnO2-based anode materials could qualify the LIBs for a safe and long-life running in low-temperature environments.

In-situ preparation of LixSn-Li2O–LiF/reduced graphene oxide composite anode material with large capacity and high initial Coulombic efficiency

Anode materials with large capacity have a growing application due to the booming electric vehicle and energy storage market. However, the low initial Coulombic efficiency (ICE) and poor cycle stability hinder their commercial development. Herein, we investigate the effective and convenient method of preparing LixSn-Li2O–LiF/reduced graphene oxide (LixSn-Li2O–LiF/RGO, Li-GFTO) composite anode material with large capacity and high ICE. Firstly, the highly-dispersed fluorine-doped tin oxide and reduced graphene oxide (F–SnO2/RGO, GFTO) composite is in-situ synthesized by one-pot reflux method. The fluorine-doped SnO2 nanocrystals are uniformly anchored on graphene sheets. Secondly, the F–SnO2/RGO was lithiated by reacting with the lithium dissolved in the solution of biphenyl and 1,2-dimethoxyethane to get LixSn-Li2O–LiF/RGO composite. The Li2O and LiF will be formed and prevent the diffusion and coarsening of Sn and LixSn during cycling. Used as the anode material, the ICE of the LixSn-Li2O–LiF/RGO composite is as high as 97%. The composite anode material also shows high cycling stability. The residual capacity is as high as 992 mAhg−1 at 0.1 Ag-1 after 100 cycles, and the charge capacity retention is 99%. Most of all, the mild preparation condition promotes the mass production and practical application of tin-lithium alloy based composite anode materials.

Alkali‐Ion Batteries: SnO2 as Advanced Anode of Alkali‐Ion Batteries: Inhibiting Sn Coarsening by Crafting Robust Physical Barriers, Void Boundaries, and Heterophase Interfaces for Superior Electrochemical Reaction Reversibility (Adv. Energy Mater. 6/2020)

Alkali‐Ion Batteries: SnO₂ as Advanced Anode of Alkali‐Ion Batteries: Inhibiting Sn Coarsening by Crafting Robust Physical Barriers, Void Boundaries, and Heterophase Interfaces for Superior Electrochemical Reaction Reversibility (Adv. Energy Mater. 6/2020)

In-situ formation of atomic-level Mn-Sn interfacial compounds for enhanced Li-ion integrated anode

High capacity nanosized SnO2 Li-ion battery anode can realize the reversible conversion of Sn/Li2O to SnO2. However, the coarsening of Sn particles leads to the incompleteness of this reversible reaction and the rapid decay of the reversible capacity. Here, an atom-level Mn–Sn interfacial composite oxide (MnSnO3) is coated on carbon fibers to form an integrated electrode by a simple in-situ technology. Ultrafine Mn nanocrystals can be uniformly dispersed around Sn nanoparticles with synergistic effect, which can effectively inhibit the coarsening of Sn and promote the high reversibility of SnO2 conversion. In addition to the porous nanostructure and binder-free properties, the prepared integrated anode exhibits initial capacity of 1350 mAh g−1 at 0.05 A g−1 with a high Coulombic efficiency of ~77.4%, superior high-rate capability, and stable long-life of more than 1000 cycles. It is hoped that this design will provide a new idea for the development of high-performance SnO2-based anodes.

SnO2 as Advanced Anode of Alkali‐Ion Batteries: Inhibiting Sn Coarsening by Crafting Robust Physical Barriers, Void Boundaries, and Heterophase Interfaces for Superior Electrochemical Reaction Reversibility

AbstractSuperior reaction reversibility of electrode materials is urgently pursued for improving the energy density and lifespan of batteries. Tin dioxide (SnO2) is a promising anode material for alkali‐ion batteries, having a high theoretical lithium storage capacity of 1494 mAh g− based on the reactions of SnO2 + 4Li+ + 4e− ↔ Sn + 2Li2O and Sn + 4.4Li+ + 4.4e− ↔ Li4.4Sn. The coarsening of Sn nanoparticles into large particles induced reaction reversibility degradation has been demonstrated as the essential failure mechanism of SnO2 electrodes. Here, three key strategies for inhibiting Sn coarsening to enhance the reaction reversibility of SnO2 are presented. First, encapsulating SnO2 nanoparticles in physical barriers of carbonaceous materials, conductive polymers or inorganic materials can robustly prevent Sn coarsening among the wrapped SnO2 nanoparticles. Second, constructing hierarchical, porous or hollow structured SnO2 particles with stable void boundaries can hinder Sn coarsening between the void‐divided SnO2 subunits. Third, fabricating SnO2‐based heterogeneous composites consisting of metals, metal oxides or metal sulfides can introduce abundant heterophase interfaces in cycled electrodes that impede Sn coarsening among the isolated SnO2 crystalline domains. Finally, a perspective on the future prospect of the structural/compositional designs of SnO2 as anode of alkali‐ion batteries is highlighted.

The Critical Size of Sn Nanograins for Achieving High Round-Trip Efficiency of Reversible Conversion Reaction in Lithiated SnO2 Nanocrystals

SnO2 has been considered one of the most promising anode materials for Li-ion batteries. However, the realization of the full capacity of SnO2 anode has been hindered mainly by the inferior reversibility of conversion (Sn+Li2O→SnO2+Li+), and especially the large initial capacity loss characterized by low initial Coulombic efficiency (ICE). In the past two decades, although many works have focused on enhancing the cycle performance of SnO2 based anodes, the achieved ICEs were still very low (<60%). Few works were devoted to understanding the fundamental reason and explore a strategy to solve this problem. Recently, we have revealed that the coarsening of Sn in the Sn/Li2O mixture, mainly induced by recrystallization, is responsible for the limited conversion of Sn/Li2O back into SnO2 during Li extraction, and achieved highly reversible conversion between Li2O and SnO2 with ICEs >86.2%, by suppressing the Sn coarsening in Li2O matrix in a sputtered SnO2 film[1]. However, it was found that the reversibility declined as the cycles increased due mainly to the gradually Sn coarsening, which was induced by the cyclic electrochemical stress (σ) imposed on the electrode[2]. Furthermore, combining nanosized transition metal with SnO2 can help to reduce the surface/interface energy of Sn nanograins and dramatically suppress the Sn coarsening, which however also affect the Coulombic efficiency and energy efficiency of the Li-SnO2 cells[3-4]. Accordingly, uncovering the critical size of Sn nanograins in lithiated SnO2 nanocrystals is of great important for enabling high round-trip efficiency of reversible conversion reaction, ensuring large stable capacity in the electrode. In this work, we report our finding that unlike the previous reports, even a pure SnO2 film consisting of nanocrystals with size around 15 nm, stable high capacity above 900mAh/g can be remained throughout 100cycles. The capacity decay in the initial dozens of cycles of SnO2 anode is mainly induced by the gradually degradation of reversible conversion reaction (Sn+Li2O←→SnO2) due to the thermal and tress driven Sn coarsening along cycles. Furthermore, as shown in Figure 1, the coarsening of Sn have reduced the reversible capacity, Coulombic efficiency, energy efficiency and Li+ ion diffusion kinetics of the SnO2 nanostructured film. The grain size of coarsening Sn (x) and the degree of irreversibility (y) monotonically increase along cycles, which is quantitatively expressed with a linear equation (y=0.0236x-0.266). It is determined that the Sn nanograins with diameters less than 11.3 nm will ensure fast interdiffusion kinetics among interfaces of Sn/Li2O for completely reversible conversion reactions, enabling full application of the high capacity of lithiated SnO2[5]. We firmly believe that these results will provide a valuable insight into designing new conversion-type electrode materials with high stable capacity for next generation rechargeable batteries. Figure 1 (a) Degree of reversibility vs. cycle number for the SnO2 film electrodes cycled among potential ranges of 0.01–3.00 and 0.01–2.00 V, respectively. (b) Average grain size and degree of irreversibility vs. cycle number. (c) Relationship between degree of irreversibility and grain size of Sn. (d) Schematic of the partially reversible conversion reaction with different grain sizes of Sn.

&lt;i&gt;In situ&lt;/i&gt; observation of lithiation mechanism of SnO&lt;sub&gt;2&lt;/sub&gt; nanoparticles

Tin oxide (SnO&lt;sub&gt;2&lt;/sub&gt;) has attracted a lot of attention among lithium ion battery anode materials due to its rich reserves, high theoretical capacity, and safe potential. However, the mechanism of the SnO&lt;sub&gt;2&lt;/sub&gt; nano materials in the lithiation-delithiation reaction, especially whether the first-step conversion reaction is reversible, is still controversial. In this paper, SnO&lt;sub&gt;2&lt;/sub&gt; nanoparticles with an average particle size of 4.4 nm are successfully prepared via a simple hydrothermal method. A nanosized lithium ion battery that enables the &lt;i&gt;in situ&lt;/i&gt; electrochemical experiments of SnO&lt;sub&gt;2&lt;/sub&gt; nanoparticles is constructed to investigate the electrochemical behavior of SnO&lt;sub&gt;2&lt;/sub&gt; in lithiation-delithiation process. Briefly, the nanosized electrochemical cell consists of a SnO&lt;sub&gt;2&lt;/sub&gt; working electrode, a metal lithium (Li) counter electrode on a sharp tungsten probe, and a solid electrolyte of lithium oxide (Li&lt;sub&gt;2&lt;/sub&gt;O) layer naturally grown on the surface of metal Li. Then, the whole lithiation-delithiation process of SnO&lt;sub&gt;2&lt;/sub&gt; nanocrystals is tracked in real time. When a constant potential of –2 V is applied to the SnO&lt;sub&gt;2&lt;/sub&gt; with respect to lithium, lithium ions begin to diffuse from one side of the nanoparticles, which is in contact with the Li/Li&lt;sub&gt;2&lt;/sub&gt;O layer, and gradually propagate to the other side. Upon the lithiation, a two-step conversion reaction mechanism is revealed: SnO&lt;sub&gt;2&lt;/sub&gt; is first converted into intermediate phase of Sn with an average diameter of 4.2 nm which is then further converted into Li&lt;sub&gt;22&lt;/sub&gt;Sn&lt;sub&gt;5&lt;/sub&gt;. Upon the delithiation, a potential of 2 V is applied and Li&lt;sub&gt;22&lt;/sub&gt;Sn&lt;sub&gt;5&lt;/sub&gt; phase can be reconverted into SnO&lt;sub&gt;2&lt;/sub&gt; phase when completely delithiated. It is because the interfaces and grain boundaries of nano-sized SnO&lt;sub&gt;2&lt;/sub&gt; may impede the Sn diffusing from one grain into another during lithiation/delithiation and then suppress the coarsening of Sn, and enable the Li&lt;sub&gt;2&lt;/sub&gt;O and Sn to be sufficiently contacted with each other and then converted into SnO&lt;sub&gt;2&lt;/sub&gt;. This work provides a valuable insight into an understanding of phase evolution in the lithiation-delithiation process of SnO&lt;sub&gt;2&lt;/sub&gt; and the results are of great significance for improving the reversible capacity and cycle performance of lithium ion batteries with SnO&lt;sub&gt;2&lt;/sub&gt; electrodes.

Unveiling critical size of coarsened Sn nanograins for achieving high round-trip efficiency of reversible conversion reaction in lithiated SnO2 nanocrystals

A pure SnO2 film consisting of SnO2 nanocrystals with a size of ~ 15nm can deliver a stable and high capacity > 900 mAhg−1 for 100 cycles. Unlike the previous perception, the capacity decay in the initial cycles of the SnO2 anode is mainly induced by the gradual degradation of the reversible conversion reaction (Sn + Li2O←→SnO2) at a potential > 1.0 V due to Sn coarsening with cycling. The coarsening of Sn has a significant impact on the reversible capacity, Coulombic efficiency, energy efficiency and Li+ ion diffusion kinetics of the SnO2 electrode. The grain size of coarsening Sn and the degree of irreversibility monotonically increase with cycling, which is quantitatively expressed with a linear equation. It is extrapolated that if the Sn grains remain with diameters < 11nm, the fast interdiffusion kinetics among the interfaces of Sn/Li2O will enable complete reversible conversion reactions in lithiated SnO2 electrodes. Since the stability of nanostructured interfaces in metal (M)/LinX (X = O, F, S) compounds is also crucial for the reversible conversion reactions in binary M-X compounds, we firmly believe that these results will provide valuable insight into the design of new conversion-type electrode materials with high and stable capacities for next-generation rechargeable batteries.