•PVDF-PMMA-PMALi ternary composite binder is firstly adopted for graphite anodes•The ternary binder can overcome the main disadvantages of a single PVDF binder•Ternary binder improves the mechanics and electrical conductivity of the anode•The optimized binder shows improved ionic conductivity, distribution and flexibility•High-rate capability and long cycling stability of graphite anodes is obtained.Herein, a poly(vinylidene fluoride)-Polymethylmethacrylate-poly(lithium methacrylate) (PVDF-PMMA-PMALi) ternary composite binder is adopted for fabricating graphite porous electrode for the first time. The graphite anode with the optimized composite binder exhibits enhanced ionic conductivity, increased flexibility of the binder matrix and significantly improved electrochemical properties compared to that with pure PVDF binder. At a very high discharge rate of 50C, the graphite electrode with ternary binder still retains ca. 96.2% of its capacity while the electrode based on PVDF binder only delivers 16.2%. Additionally, high reversible capacity retentions are obtained to be 86.6, 50.1 and 21.9% of its reversible capacity at 0.1C at the same charge/discharge rates of 1C, 2C and 5C, respectively. These results enable us to get deep insight into the rational design of blended binder with interior synergistic effect for high-rate and long-life Li-ion battery anodes.

Silicon is regarded as one of the most promising anode materials for next generation Li-ion batteries (LIBs). However, for the actual applications, a Si electrode must possess superior electrochemical properties, and the fabrication must be cost-effective and industrially scalable. Here, we report a highly scalable and low-cost route of recovering high-purity Si micro-plates from photovoltaic industry waste obtained during diamond-wire slicing of solar grade Si ingots, and demonstrate their great potential as high-performance anode materials with ideal cost. To accommodate the severe volume effect of Si micro-plates, a firmly anchored alginate coating layer is formed on the Si surface on the basis of the strong interactions between the oxidized Si and alginate carboxylic groups, which helps to construct a robust conductive network around Si micro-plates and allows the electrode architecture to be perfectly maintained even though the Si micro-plates are pulverized into nanoparticles. The recycled Si anode delivers high reversible capacity, superior rate capability and extraordinary cyclability. This new technology not only provides an abundant and low-cost Si source for LIB applications, but also effectively resolves the waste disposal issue of the photovoltaic industry, which may therefore bring about enormous environmental and economic benefits.

A silicon-based anode material offers extremely high lithium storage capacity, but suffers from severe volume expansion during lithiation, which causes a drastic capacity decay. Embedding and isolating Si nanoparticles (SiNPs) into sealed amorphous carbon hollow spheres with sufficient voids is a promising strategy to accommodate the volume effect of Si. However, the created voids significantly compromise the volumetric energy density. Conversely, if insufficient voids are introduced, the inferior mechanical property of the amorphous carbon turns into the decisive factor destroying the structural integrity of the composites. Graphene is more suitable as a protective shell material due to its excellent mechanical strength. However, there still remains a formidable challenge of constructing closed graphene hollow spheres owing to their unique two-dimensional structure. Herein, we first propose a bottom-up route to controllably synthesize a polycrystalline graphene hollow sphere isolated SiNP nanocomposite (Si@void@graphene) through an in situ pyrolysis and metal-catalyzed graphitization reaction, in which glucose and metal sulfate with strictly controlled content and ratio are employed as the carbon source and catalyst precursor, respectively. The obtained graphene hollow spheres with superb mechanical properties offer a permanent structural and electrical environment for the inner SiNPs even insufficient voids are introduced while maintaining a reasonable volumetric energy density. When the void space is designed based on the assumption that Si has only 250% volume change, the Si@void@graphene electrode exhibits high reversible capacity, superior rate capability and much prolonged cycle life as compared to those of the Si@void@amorphous carbon electrode.

In the past decade, there have been great advances in the controllable growth of two-dimensional (2D) graphene sheets. However, the preparation of 3D structured graphene such as graphene coatings on arbitrary-shaped micro/nano materials still remains a formidable challenge. Herein, we have proposed a general strategy for the in situ growth of 3D graphene coatings on the micro/nano particles with arbitrary shapes. Inspired by the CVD growth mechanism of 2D graphene sheets on the bulk metal substrates, we have in situ constructed a nanometer-thick catalytic interface on the micro/nano particle surface by introducing a trace amount of transition metal salts and solid carbon sources with strictly-controlled content and ratio. Growth of 3D graphene coatings is accomplished through a solid-state reaction. Under the catalysis of the in situ formed catalytic interface consisting of highly-ordered metal nanoislands, the nano-thick amorphous carbon layer which arousing from the pyrolysis of carbon sources can be effectively transformed into a continuous and uniform graphene coating throughout the material surface based on a “dissolution–precipitation” mechanism. 3D graphene coatings have been successfully grown on lithium iron phosphate, silver, copper and silicon particles. The growth mechanism of the 3D graphene coatings has been studied in detail and a growth model is also proposed.

•A binary solvent electrolyte containing TFPC and PC is used for high-voltage LIBs.•Volume ratio of TFPC/PC is a crucial factor affecting the physical and electrochemical properties.•The binary solvent can maintain a stable liquid phase in a broad temperature range.•Graphite anode works well in the electrolyte of 1 mol dm−3 LiPF6-TFPC/PC (1:2).•The optimized electrolyte has good compatibility with 5 V LiNi0.5Mn1.5O4 cathode.To widen the operating potential window of electrolyte used for lithium-ion batteries, a binary cyclic carbonates-based electrolyte containing propylene carbonate (PC) and trifluoropropylene carbonate (TFPC) with an optimized volume ratio has been successfully proposed. The main function of additive TFPC is to establish a stable SEI layer on graphite electrode and suppress the intercalation reaction of PC molecules. Unlike the previous works, where the TFPC/PC involved electrolyte was simply estimated at a certain volume ration and recognized as an unfavorable system, in this work, the physical properties of the electrolyte solutions with a series of volume ratios of TFPC/PC and their electrochemical performances in a graphite/Li cell and 5 V LiNi0.5Mn1.5O4/Li cell have been systematically studied. The electrolyte of 1 mol dm−3 LiPF6-TFPC/PC (1:2) is adopted as the optimized system due to its high ionic conductivity, low viscosity, broad operating potential window, wide liquid temperature range (−50 ∼ 240 °C) and suitable film-forming property. Both the graphite and LiNi0.5Mn1.5O4 electrodes were found to exhibit high reversible capacity and superb rate performance in the optimized electrolyte, making us have a new recognition of this important binary solvent. Considering its excellent physical and electrochemical properties, we therefore anticipate that the electrolyte based on TFPC and PC is a possible candidate for future LIBs that can work in a broader temperature range and high operation potential conditions.A binary cyclic carbonates-based electrolyte containing propylene carbonate and trifluoropropylene carbonate with an optimized volume ratio is successfully applied for 5 V lithium-ion batteries.

Silicon offers an extremely high theoretical specific capacity, but suffers from dramatic volume change during lithiation/delithiation processes, which typically leads to rapid anode degradation. Here we designed a facile and self-assembly strategy to construct a three-dimensional (3D) polymeric network as a promising binder for high-performance silicon submicro-particle (SiSMP) anodes through in situ interconnection of alginate chains by additive divalent cations. The highly cross-linked alginate network exhibits superb mechanical properties and strongly interacts with SiSMPs, which can tolerate the volume change of SiSMPs and restrict the volume expansion of the laminates to a large degree, thus effectively maintaining the mechanical and electrical integrity of the electrode and significantly improving the electrochemical performance. As a result, SiSMPs with a 3D binder network exhibit high reversible capacity, superior rate capability and much prolonged cycle life. Additionally, the 3D alginate binder was also successfully applied for the industrial submicro-silicon waste from solar cell production. With all of the advantages, the innovative way to tolerate the severe volume change by using a high-strength polymeric network may open a new approach to realize the industrial application of Si-based anodes in lithium-ion batteries.

Two-level hierarchical structured LiMnPO4/C granules consisting of LiMnPO4 primary nanoparticles (5–10 nm) and a 3-dimensional conductive carbon skeleton are synthesized through a facile surfactant-assisted solid-state reaction. The small size of primary nanoparticles greatly shortens the diffusion distance of Li ions and the 3D conductive carbon network ensures the electrical continuity throughout the granule. The as-prepared LiMnPO4 cathode with 7.5 wt% carbon exhibits a high specific capacity and superior rate performance with discharge capacities of 130.1 mA h g−1 at 0.05 C, 116.3 mA h g−1 at 1 C and 60.1 mA h g−1 at 20 C. Meanwhile, it can retain 97.5% of the initial capacity after 50 cycles at 0.1 C, revealing a stable cycling stability. Therefore this material has great potential application for advanced Li-ion batteries.

•Graphene-decorated LiFePO4 is in-situ synthesized through solid-state reaction.•Graphene is in-situ grown through pyrolysis and catalytic graphitization of glucose.•Graphene forms a compact, uniform and thin coating layer throughout the LFP NPs.•Graphene cross-links into a conducting network around the LFP NPs.•Electrochemical performance of LFP@graphene is remarkably improved.Graphene-decorated LiFePO4 composite is synthesized for the first time through in-situ pyrolysis and catalytic graphitization, in which glucose and a trace amount of FeSO4 are employed as the graphene source and catalyst precursor, respectively. Under Ar/H2 (95:5) atmosphere at 750 °C, FeSO4 is thermally reduced to Fe nano-particles (Fe NPs) and glucose is pyrolyzed to carbon fragments first, followed by the in-situ growth of graphene sheets directly on the LiFePO4 nano-particles (LFP NPs) surface through the realignment of carbon fragments under the catalytic effect of the Fe NPs. The graphene sheets not only form a compact and uniform coating layer throughout the LFP NPs, but also stretch out and cross-link into a conducting network around the LFP particles. The LiFePO4@graphene composite displays a high reversible specific capacity of 167.7 mAh g−1 at 0.1C rate, superb rate performance with discharge capacity of 94.3 mAh g−1 at 100C rate and much prolonged cycle life. The remarkable electrochemical improvement is attributed to both electric and ionic conductivity increase as a result of in-situ grown graphene coatings along the LFP surface and the graphene network intrinsically connecting to the LFP particles.

•The effect of Li-salt mixing in LiPF6/EC/EMC electrolyte is investigated.•The corrosion of Al by LiFSI is successfully suppressed by the addition of LiBOB.•The high surface impedance arising from LiBOB is reduced by the presence of LiFSI.•Electrochemical behaviour of the graphite anode and the LiFePO4 cathode is improved by Li-salt mixing.The effect of Li-salt mixing in Li-ion battery electrolyte based on LiPF6 in ethylene carbonate (EC) and ethyl methyl carbonate (EMC) is investigated. The addition of an appropriate amount of lithium bis(fluorosulfonyl)imide (LiFSI) into the LiPF6-based electrolyte contributes to an electrochemical improvement of the graphite anode. However, the LiFePO4 cathode is difficult to cycle in such an electrolyte due to the severe corrosion of the aluminium current collector by FSI anions. Lithium bis-oxalato borate (LiBOB) is able to passivate Al and suppress the corrosion arising from the FSI anions. An improvement of rate performance and cycling stability for both the LiFePO4 cathode and the graphite anode is obtained in 1.0 mol L−1 LiPF6/EC/EMC electrolyte containing 0.2 mol L−1 LiFSI and 0.2 mol L−1 LiBOB salts.Moreover, an excellent compatibility between the graphite anode and LiFePO4 cathode in the ternary-salt electrolyte system is further confirmed by the full cell tests. The electrochemical performance improvement of the electrolyte resulting from Li-salt mixing provides a new way for optimization of electrolyte for high performance Li-ion batteries.

The synthesis of graphene-based composite materials for Li-ion batteries using an in situ growing technique is first proposed in this work. Graphene frame supported silicon@graphitic carbon granules were obtained through a one-step solid-state reaction using iron phthalocyanine (FePc) and silicon nanoparticles (SiNPs) as the precursors. Nitrogen-doped graphene was grown in situ around the SiNPs by pyrolyzing and re-carbonizing FePc, and a cross-linked graphene frame network was gradually formed. Simultaneously, SiNPs were wrapped by a thin graphitic carbon layer, and the strong interconnections between the graphene, graphitic carbon and SiNPs led to a spontaneous self-assembly process, resulting in the formation of μm scale granules with available nanoporosities and irregular channels. The self-assembled granules with excellent electrical conductivity can effectively accommodate the volume change of the SiNPs during the repeating discharge–charge processes, therefore high capacity, long cycle life, high Coulombic efficiency and superb rate capability have been realized. The synthesis strategy is facile, safe, low-cost and can be easily industrialized, providing a broadly applicable route for the in situ synthesis of more functional graphene-based composite materials.

•Chitosan is used as a new electrode binder for graphite anode.•Electrochemical properties of the chitosan-based electrode are compared with that of PVDF-based one.•Electrochemical performances of the graphite anode are improved by using chitosan binder.•Chitosan binder facilitates the formation of a thin, homogenous and stable SEI film of the electrode.Chitosan was applied as the electrode binder material for a spherical graphite anode in lithium-ion batteries. Compared to using poly (vinylidene fluoride) (PVDF) binder, the graphite anode using chitosan exhibited enhanced electrochemical performances in terms of the first Columbic efficiency, rate capability and cycling behavior. With similar specific capacity, the first Columbic efficiency of the chitosan-based anode is 95.4% compared to 89.3% of the PVDF-based anode. After 200 charge–discharge cycles at 0.5C, the capacity retention of the chitosan-based electrode showed to be significantly higher than that of the PVDF-based electrode. Electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) measurements were carried out to investigate the formation and evolution of the solid electrolyte interphase (SEI) formed on the graphite electrodes. The results show that a thin, homogenous and stable SEI layer is formed on the graphite electrode surface with chitosan binder compared with that using the conventional PVDF binder

The synthesis of graphene-based composite materials for Li-ion batteries using an in situ growing technique is first proposed in this work. Graphene frame supported silicon@graphitic carbon granules were obtained through a one-step solid-state reaction using iron phthalocyanine (FePc) and silicon nanoparticles (SiNPs) as the precursors. Nitrogen-doped graphene was grown in situ around the SiNPs by pyrolyzing and re-carbonizing FePc, and a cross-linked graphene frame network was gradually formed. Simultaneously, SiNPs were wrapped by a thin graphitic carbon layer, and the strong interconnections between the graphene, graphitic carbon and SiNPs led to a spontaneous self-assembly process, resulting in the formation of μm scale granules with available nanoporosities and irregular channels. The self-assembled granules with excellent electrical conductivity can effectively accommodate the volume change of the SiNPs during the repeating discharge–charge processes, therefore high capacity, long cycle life, high Coulombic efficiency and superb rate capability have been realized. The synthesis strategy is facile, safe, low-cost and can be easily industrialized, providing a broadly applicable route for the in situ synthesis of more functional graphene-based composite materials.

Two-level hierarchical structured LiMnPO4/C granules consisting of LiMnPO4 primary nanoparticles (5–10 nm) and a 3-dimensional conductive carbon skeleton are synthesized through a facile surfactant-assisted solid-state reaction. The small size of primary nanoparticles greatly shortens the diffusion distance of Li ions and the 3D conductive carbon network ensures the electrical continuity throughout the granule. The as-prepared LiMnPO4 cathode with 7.5 wt% carbon exhibits a high specific capacity and superior rate performance with discharge capacities of 130.1 mA h g−1 at 0.05 C, 116.3 mA h g−1 at 1 C and 60.1 mA h g−1 at 20 C. Meanwhile, it can retain 97.5% of the initial capacity after 50 cycles at 0.1 C, revealing a stable cycling stability. Therefore this material has great potential application for advanced Li-ion batteries.

A silicon-based anode material offers extremely high lithium storage capacity, but suffers from severe volume expansion during lithiation, which causes a drastic capacity decay. Embedding and isolating Si nanoparticles (SiNPs) into sealed amorphous carbon hollow spheres with sufficient voids is a promising strategy to accommodate the volume effect of Si. However, the created voids significantly compromise the volumetric energy density. Conversely, if insufficient voids are introduced, the inferior mechanical property of the amorphous carbon turns into the decisive factor destroying the structural integrity of the composites. Graphene is more suitable as a protective shell material due to its excellent mechanical strength. However, there still remains a formidable challenge of constructing closed graphene hollow spheres owing to their unique two-dimensional structure. Herein, we first propose a bottom-up route to controllably synthesize a polycrystalline graphene hollow sphere isolated SiNP nanocomposite (Si@void@graphene) through an in situ pyrolysis and metal-catalyzed graphitization reaction, in which glucose and metal sulfate with strictly controlled content and ratio are employed as the carbon source and catalyst precursor, respectively. The obtained graphene hollow spheres with superb mechanical properties offer a permanent structural and electrical environment for the inner SiNPs even insufficient voids are introduced while maintaining a reasonable volumetric energy density. When the void space is designed based on the assumption that Si has only 250% volume change, the Si@void@graphene electrode exhibits high reversible capacity, superior rate capability and much prolonged cycle life as compared to those of the Si@void@amorphous carbon electrode.

Silicon is regarded as one of the most promising anode materials for next generation Li-ion batteries (LIBs). However, for the actual applications, a Si electrode must possess superior electrochemical properties, and the fabrication must be cost-effective and industrially scalable. Here, we report a highly scalable and low-cost route of recovering high-purity Si micro-plates from photovoltaic industry waste obtained during diamond-wire slicing of solar grade Si ingots, and demonstrate their great potential as high-performance anode materials with ideal cost. To accommodate the severe volume effect of Si micro-plates, a firmly anchored alginate coating layer is formed on the Si surface on the basis of the strong interactions between the oxidized Si and alginate carboxylic groups, which helps to construct a robust conductive network around Si micro-plates and allows the electrode architecture to be perfectly maintained even though the Si micro-plates are pulverized into nanoparticles. The recycled Si anode delivers high reversible capacity, superior rate capability and extraordinary cyclability. This new technology not only provides an abundant and low-cost Si source for LIB applications, but also effectively resolves the waste disposal issue of the photovoltaic industry, which may therefore bring about enormous environmental and economic benefits.

Silicon offers an extremely high theoretical specific capacity, but suffers from dramatic volume change during lithiation/delithiation processes, which typically leads to rapid anode degradation. Here we designed a facile and self-assembly strategy to construct a three-dimensional (3D) polymeric network as a promising binder for high-performance silicon submicro-particle (SiSMP) anodes through in situ interconnection of alginate chains by additive divalent cations. The highly cross-linked alginate network exhibits superb mechanical properties and strongly interacts with SiSMPs, which can tolerate the volume change of SiSMPs and restrict the volume expansion of the laminates to a large degree, thus effectively maintaining the mechanical and electrical integrity of the electrode and significantly improving the electrochemical performance. As a result, SiSMPs with a 3D binder network exhibit high reversible capacity, superior rate capability and much prolonged cycle life. Additionally, the 3D alginate binder was also successfully applied for the industrial submicro-silicon waste from solar cell production. With all of the advantages, the innovative way to tolerate the severe volume change by using a high-strength polymeric network may open a new approach to realize the industrial application of Si-based anodes in lithium-ion batteries.