A porous silicon anode prepared by dealloying a Sr-modified Al–Si eutectic alloy for lithium ion batteries

Silicon has been considered to be one of the most promising anode materials for next generation lithium ion batteries due to its high theoretical specific capacity. However, its huge volume expansion during the lithiation/delithiation process that can result in rapid capacity fading and low conductivity present significant challenges for application. In this study, the morphology of Si in an Al–Si eutectic alloy was modified by Sr, and porous Si was then produced by dealloying the precursor. Profiting from the unique structure, the Si anode exhibits an excellent reversible capacity of 405 mA h g⁻¹ at 0.5 A g⁻¹ after 100 cycles and a fantastic first cycle coulombic efficiency of 83.74%. Furthermore, the porous silicon modified by Sr delivers a stable capacity of 594.8 mA h g⁻¹ even at a high current density of 2 A g⁻¹ after 50 cycles, suggesting a good rate capability.

With a porous coralloid structure, the silicon anode prepared by dealloying the Sr-modified Al–Si eutectic alloy exhibits excellent cycle and rate performances.     

Rapid fabrication of porous silicon/carbon microtube composites as anode materials for lithium-ion batteries

Herein, we present a simple and rapid method to synthesize porous silicon/carbon microtube composites (PoSi/CMTs) by adopting a unique configuration of acid etching solution. The CMTs can act as both conductive agent and buffer for Si volume change during the charge and discharge process. The highly reversible capacity and excellent rate capability can be ascribed to the structure, where porous silicon powders are wrapped by a network of interwoven carbon microtubes. The composites show specific capacities of more than 1712 mA h g⁻¹ at a current density of 100 mA g⁻¹, 1566 mA h g⁻¹ at 200 mA g⁻¹, 1407 mA h g⁻¹ at 400 mA g⁻¹, 1177 mA h g⁻¹ at 800 mA g⁻¹, 1107 mA h g⁻¹ at 1000 mA g⁻¹, 798 mA hg⁻¹ at 2000 mA g⁻¹, and 581 mA h g⁻¹ at 3000 mA g⁻¹ and maintain a value of 1127 mA h g⁻¹ after 100 cycles at a current density of 200 mA g⁻¹. Electrochemical impedance spectroscopy (EIS) measurements prove that charge transfer resistance of PoSi/CMT composites is smaller than that of pure PoSi. In this study, we propose a quick, economical and feasible method to prepare silicon-based anode materials for lithium-ion batteries.

We added additives to the acid etching solution and prepared the silicon/carbon microtubes composites using a simple and fast method.     

Structure and conductivity enhanced treble-shelled porous silicon as an anode for high-performance lithium-ion batteries

Silicon is regarded as the next generation anode material for lithium-ion batteries because of its high specific capacity, low intercalation potential and abundant reserves. However, huge volume changes during the lithiation and delithiation processes and low electrical conductivity obstruct the practical applications of silicon anodes. In this study, a treble-shelled porous silicon (TS-P-Si) structure was synthesized via a three-step approach. The TS-P-Si anode delivered a capacity of 858.94 mA h g⁻¹ and a capacity retention of 87.8% (753.99 mA h g⁻¹) after being subjected to 400 cycles at a current density of 400 mA g⁻¹. The good cycling performance was due to the unique structure of the inner silicon oxide layer, middle silver nano-particle layer and outer carbon layer, leading to a good conductivity and a decreased volume change of this silicon-based anode.

In this paper, a treble-shelled porous silicon structure is synthesized through three-step approach to enhance the structural stability and conductivity.     

Hard carbon spheres prepared by a modified Stöber method as anode material for high-performance potassium-ion batteries

The Stöber method is a highly efficient synthesis strategy for homogeneous monodisperse polymer colloidal spheres and carbon spheres. This work delivers an extended Stöber method and investigates the synthesis process. By calcining the precursor under appropriate conditions, solid secondary particles of amorphous carbon (SSAC) and hollow secondary particles of graphitized carbon (HSGC) can be directly synthesized. The two materials have a nano-primary particle structure and a closely-packed sub-micron secondary particle structure, which can be used in energy storage. We find that SSAC and HSGC have high potassium-ion storage capacity with reversible capacities of 274 mA h g⁻¹ and 283 mA h g⁻¹ at 20 mA g⁻¹ respectively. Significantly, SSAC has better rate performance with a specific capacity of 107 mA h g⁻¹ at 1 A g⁻¹.

A modified Stöber method synthesizes resorcinol-formaldehyde resin-based secondary particle hard carbon spheres as anode material for high-performance potassium-ion batteries.     

Preparation of cobalt sulfide@reduced graphene oxide nanocomposites with outstanding electrochemical behavior for lithium-ion batteries

Cobalt sulfide@reduced graphene oxide composites were prepared through a simple solvothermal method. The cobalt sulfide@reduced graphene oxide composites are composed of cobalt sulfide nanoparticles uniformly attached on both sides of reduced graphene oxide. Some favorable electrochemical performances in specific capacity, cycling performance, and rate capability are achieved using the porous nanocomposites as an anode for lithium-ion batteries. In a half-cell, it exhibits a high specific capacity of 1253.9 mA h g⁻¹ at 500 mA g⁻¹ after 100 cycles. A full cell consists of the cobalt sulfide@reduced graphene oxide nanocomposite anode and a commercial LiCoO₂ cathode, and is able to hold a high capacity of 574.7 mA h g⁻¹ at 200 mA g⁻¹ after 200 cycles. The reduced graphene oxide plays a key role in enhancing the electrical conductivity of the electrode materials; and it effectively prevents the cobalt sulfide nanoparticles from dropping off the electrode and buffers the volume variation during the discharge–charge process. The cobalt sulfide@reduced graphene oxide nanocomposites present great potential to be a promising anode material for lithium-ion batteries.

Cobalt sulfide@reduced graphene oxide nanocomposites obtained through a dipping and hydrothermal process, exhibit ascendant lithium-ion storage properties.     

Performance optimization of freestanding MWCNT-LiFePO4 sheets as cathodes for improved specific capacity of lithium-ion batteries

The typical lithium-ion-battery positive electrode of “lithium-iron phosphate (LiFePO₄) on aluminum foil” contains a relatively large amount of inactive materials of 29 wt% (22 wt% aluminum foil + 7 wt% polymeric binder and graphitic conductor) which limits its maximum specific capacity to 120.7 mA h g⁻¹ (71 wt% LiFePO₄) instead of 170 mA h g⁻¹ (100 wt% LiFePO₄). We replaced the aluminum current-collector with a multi-walled carbon nanotube (MWCNT) network. We optimized the specific capacity of the “freestanding MWCNT-LiFePO₄” positive electrode. Through the optimization of our unique surface-engineered tape-cast fabrication method, we demonstrated the amount of LiFePO₄ active materials can be as high as 90 wt% with a small amount of inactive material of 10 wt% MWCNTs. This translated to a maximum specific capacity of 153 mA h g⁻¹ instead of 120.7 mA h g⁻¹, which is a significant 26.7% gain in specific capacity compared to conventional cathode design. Experimental data of the freestanding MWCNT-LiFePO₄ at a low discharge rate of 17 mA g⁻¹ show an excellent specific capacity of 144.9 mA h g⁻¹ which is close to its maximum specific capacity of 153 mA h g⁻¹. Furthermore, the freestanding MWCNT-LiFePO₄ has an excellent specific capacity of 126.7 mA h g⁻¹ after 100 cycles at a relatively high discharge rate of 170 mA g⁻¹ rate.

We optimized the specific capacity of freestanding MWCNT-LiFePO₄ positive electrode. We demonstrated as high (low) as 90 wt% LiFePO₄ active material (10 wt% MWCNTs inactive material). This corresponded to a maximum specific capacity of 153 mA h g⁻¹.     

SnS/C nanocomposites for high-performance sodium ion battery anodes

Sodium-ion batteries have been considered as one of the most promising types of batteries, beyond lithium-ion batteries, for large-scale energy storage applications. However, their deployment hinges on the development of new anode materials, since it has been shown that many important anode materials employed in lithium ion batteries, such as graphite and silicon, are inadequate for sodium-ion batteries. We have simply prepared novel SnS/C nanocomposites through a top-down approach as anode materials for sodium-ion batteries. Their electrochemical performance has been significantly improved when compared to bare SnS, especially in terms of cycling stability and rate capabilities. SnS/C nanocomposites exhibit excellent capacity retention, at various current rates, and deliver capacities as high as 400 mA h g⁻¹ even at the high current density of 800 mA g⁻¹ (2C). Ex situ transmission electron microscopy, X-ray diffraction and operando X-ray absorption near edge structure studies have been performed in order to unravel the reaction mechanism of the SnS/C nanocomposites.

SnS/C nanocomposites were simply prepared as anode materials for sodium-ion batteries. They showed excellent cycling stability at various current densities with more than 90% of its capacity delivered when the current increased from 50 to 500 mA g⁻¹.     

Hydrothermal-template synthesis and electrochemical properties of Co3O4/nitrogen-doped hemisphere-porous graphene composites with 3D heterogeneous structure

Despite the high capacity of Co₃O₄ employed in lithium-ion battery anodes, the reduced conductivity and grievous volume change of Co₃O₄ during long cycling of insertion/extraction of lithium-ions remain a challenge. Herein, an optimized nanocomposite, Co₃O₄/nitrogen-doped hemisphere-porous graphene composite (Co₃O₄/N-HPGC), is synthesized by a facile hydrothermal-template approach with polystyrene (PS) microspheres as a template. The characterization results demonstrate that Co₃O₄ nanoparticles are densely anchored onto graphene layers, nitrogen elements are successfully introduced by carbamide and the nanocomposites maintain the hemispherical porous structure. As an anode material for lithium-ion batteries, the composite material not only maintains a relatively high lithium storage capacity (the first discharge specific capacity can reach 2696 mA h g⁻¹), but also shows significantly improved rate performance (1188 mA h g⁻¹ at 0.1 A g⁻¹, 344 mA h g⁻¹ at 5 A g⁻¹) and enhanced cycling stability (683 mA h g⁻¹ after 500 cycles at 1 A g⁻¹). The enhanced electrochemical properties of Co₃O₄/N-HPGC nanocomposites can be ascribed to the synergistic effects of Co₃O₄ nanoparticles, novel hierarchical structure with hemisphere-pores and nitrogen-containing functional groups of the nanomaterials. Therefore, the developed strategy can be extended as a universal and scalable approach for integrating various metal oxides into graphene-based materials for energy storage and conversion applications.

The Co₃O₄/N-HPGC nanocomposites synthesized by a hydrothermal-template approach with polystyrene microspheres as the template possess excellent electrochemical performance.     

Ultrafine MoO2 nanoparticles encapsulated in a hierarchically porous carbon nanofiber film as a high-performance binder-free anode in lithium ion batteries

Flexible free-standing hierarchically porous carbon nanofibers embedded with ultrafine (∼3.5 nm) MoO₂ nanoparticles (denoted as MoO₂@HPCNFs) have been synthesized by electrospinning and subsequent heat treatment. When evaluated as a binder-free anode in Li-ion batteries, the as-obtained MoO₂@HPCNFs film exhibits excellent capacity retention with high reversible capacity (≥1055 mA h g⁻¹ at 100 mA g⁻¹) and good rate capability (425 mA h g⁻¹ at 2000 mA g⁻¹), which is much superior to most of the previously reported MoO₂-based materials. The synergistic effect of uniformly dispersed ultrasmall MoO₂ nanoparticles and a three-dimensionally hierarchical porous conductive network constructed by HPCNFs effectively improve the utilization rate of active materials, enhance the transport of both electrons and Li⁺ ions, facilitate the electrolyte penetration, and promote the Li⁺ storage kinetics and stability, thus leading to a greatly enhanced electrochemical performance.

A novel binder-free LIB anode made of ultrafine MoO₂ nanoparticles encapsulated in hierarchically porous carbon nanofibers exhibits high Li-storage performance.     

Hierarchical porous ZnMnO3 yolk–shell microspheres with superior lithium storage properties enabled by a unique one-step conversion mechanism

ZnMnO₃ has attracted enormous attention as a novel anode material for rechargeable lithium-ion batteries due to its high theoretical capacity. However, it suffers from capacity fading because of the large volumetric change during cycling. Here, porous ZnMnO₃ yolk–shell microspheres are developed through a facile and scalable synthesis approach. This ZnMnO₃ can effectively accommodate the large volume change upon cycling, leading to an excellent cycling stability. When applying this ZnMnO₃ as the anode in lithium-ion batteries, it shows a remarkable reversible capacity (400 mA h g⁻¹ at a current density of 400 mA g⁻¹ and 200 mA h g⁻¹ at 6400 mA g⁻¹) and excellent cycling performance (540 mA h g⁻¹ after 300 cycles at 400 mA g⁻¹) due to its unique structure. Furthermore, a novel conversion reaction mechanism of the ZnMnO₃ is revealed: ZnMnO₃ is first converted into intermediate phases of ZnO and MnO, after which MnO is further reduced to metallic Mn while ZnO remains stable, avoiding the serious pulverization of the electrode brought about by lithiation of ZnO.

ZnMnO₃ has attracted enormous attention as a novel anode material for rechargeable lithium-ion batteries due to its high theoretical capacity.     

Synthesis of hierarchical Sn/SnO nanosheets assembled by carbon-coated hollow nanospheres as anode materials for lithium/sodium ion batteries

Tin-based anode materials have aroused interest due to their high capacities. Nevertheless, the volume expansion problem during lithium insertion/extraction processes has severely hindered their practical application. In particular, nano–micro hierarchical structure is attractive with the integrated advantages of nano-effect and high thermal stability of the microstructure. Herein, hierarchical Sn/SnO nanosheets assembled by carbon-coated hollow nanospheres were successfully synthesized by a facile glucose-assisted hydrothermal method, in which the glucose served as both morphology-control agent and carbon source. The hierarchical Sn/SnO nanosheets exhibit excellent electrochemical performances owing to the unique configuration and carbon coating. Specifically, a reversible high capacity of 2072.2 mA h g⁻¹ was observed at 100 mA g⁻¹. Further, 964.1 mA h g⁻¹ after 100 cycles at 100 mA g⁻¹ and 820.4 mA h g⁻¹ at 1000 mA g⁻¹ after 300 cycles could be obtained. Encouragingly, the Sn/SnO also presents certain sodium ion storage properties. This facile synthetic strategy may provide new insight into fabricating high-performance Sn-based anode materials combining the advantages of both structure and carbon coating.

Hierarchical Sn/SnO nanosheets assembled by carbon-coated hollow nanospheres with promising lithium and sodium storage performances.     

ZnSe nanoparticles dispersed in reduced graphene oxides with enhanced electrochemical properties in lithium/sodium ion batteries

A ZnSe-reduced graphene oxide (ZnSe-rGO) nanocomposite with ZnSe dispersed in rGO is prepared via a one-step hydrothermal method and applied as the anode materials for both lithium and sodium ion batteries (LIBs/SIBs). The as-prepared composite exhibits greatly enhanced reversible capacity, excellent cycling stability and rate capability (530 mA h g⁻¹ after 100 cycles at 500 mA g⁻¹ in LIBs, 259.5 mA h g⁻¹ after 50 cycles at the current density of 100 mA g⁻¹ in SIBs) compared with bare ZnSe in both lithium and sodium storage. The rGO plays an influential role in enhancing the conductivity of the nanocomposites, buffering the volume change and preventing the aggregation of ZnSe particles during the cycling process, thus securing the high structure stability and reversibility of the electrode.

ZnSe-rGO nanocomposite with ZnSe dispersed in reduced graphene oxides is studied as an anode for lithium and sodium ion batteries (LIBs/SIBs).     

Preparation of novel two-stage structure MnO micrometer particles as lithium-ion battery anode materials

MnO micrometer particles with a two-stage structure (composed of mass nanoparticles) were produced via a one-step hydrothermal method using histidine and potassium permanganate (KMnO₄) as reagents, with subsequent calcination in a nitrogen (N₂) atmosphere. When the MnO micrometer particles were utilized in lithium-ion batteries (LIBs) as anode materials, the electrode showed a high reversible specific capacity of 747 mA h g⁻¹ at 100 mA g⁻¹ after 100 cycles, meanwhile, the electrode presented excellent rate capability at various current densities from 100 to 2000 mA g⁻¹ (∼203 mA h g⁻¹ at 2000 mA g⁻¹). This study developed a new approach to prepare two-stage structure micrometer MnO particles and the sample can be a promising anode material for lithium-ion batteries.

MnO micrometer particles with a two-stage structure (composed of mass nanoparticles) were produced via a one-step hydrothermal method using histidine and potassium permanganate (KMnO₄) as reagents, with subsequent calcination in a nitrogen (N₂) atmosphere.     

Highly crystalline nickel hexacyanoferrate as a long-life cathode material for sodium-ion batteries

Prussian blue analogs (PBAs) are attractive cathode candidates for high energy density, including long life-cycle rechargeable batteries, due to their non-toxicity, facile synthesis techniques and low cost. Nevertheless, traditionally synthesized PBAs tend to have a flawed crystal structure with a large amount of [Fe(CN)₆]⁴⁻ openings and the presence of crystal water in the framework; therefore the specific capacity achieved has continuously been low with poor cycling stability. Herein, we demonstrate low-defect and sodium-enriched nickel hexacyanoferrate nanocrystals synthesized by a facile low-speed co-precipitation technique assisted by a chelating agent to overcome these problems. As a consequence, the prepared high-quality nickel hexacyanoferrate (HQ-NiHCF) exhibited a high specific capacity of 80 mA h g⁻¹ at 15 mA g⁻¹ (with a theoretical capacity of ∼85 mA h g⁻¹), maintaining a notable cycling stability (78 mA h g⁻¹ at 170 mA g⁻¹ current density) without noticeable fading in capacity retention after 1200 cycles. This low-speed synthesis strategy for PBA-based electrode materials could be also extended to other energy storage materials to fabricate high-performance rechargeable batteries.

A low-speed synthesis strategy was designed to fabricate Prussian blue analog based electrode materials for high-performance rechargeable batteries.     

Amorphous red phosphorus incorporated with pyrolyzed bacterial cellulose as a free-standing anode for high-performance lithium ion batteries

Amorphous red phosphorus/pyrolyzed bacterial cellulose (P-PBC) free-standing films are prepared by thermal carbonization and a subsequent vaporization-condensation process. The distinctive bundle-like structure of the flexible pyrolyzed bacterial cellulose (PBC) matrix not only provides sufficient volume to accommodate amorphous red-phosphorus (P) but also restricts the pulverization of red-P during the alternate lithiation/delithiation process. When the mass ratio of raw materials, red-P to PBC, is 70 : 1, the free-standing P-PBC film anode exhibits high reversible capacity based on the mass of the P-PBC film (1039.7 mA h g⁻¹ after 100 cycle at 0.1C, 1C = 2600 mA g⁻¹) and good cycling stability at high current density (capacity retention of 82.84% after 1000 cycles at 2C), indicating its superior electrochemical performances.

A novel freestanding anode was prepared by combining amorphous red-P with a pyrolyzed bacterial cellulose (PBC) matrix for the first time.     

Glucose hydrothermal encapsulation of carbonized silicone polyester to prepare anode materials for lithium batteries with improved cycle stability

A silicon polyester (Si-PET) was synthesized with ethylene glycol and phthalic anhydride, and then it was carbonized and hydrothermally coated with glucose. The formed SiO_x with layered graphene as the 3D network had an amorphous carbon layer. The graphene oxide (rGO) after carbothermal reduction was completely retained in SiO_x, which improved the conductivity of the SiO_x anode material. SiO_x were encapsulated with a flexible amorphous carbon layer on the surface, which can not only improve the electrical performance, but also effectively relieve the huge volume changes of the compound. Further, the key point is that, the solid electrolyte interphase (SEI) film was mainly formed on the surface carbon layer. This would keep a stable SEI film during volume pulverization, and result in a good cycle stability. The SiO_x/C-rGO material maintained a reversible capacity of 660 mA h g⁻¹ at a current density of 100 mA g⁻¹ for 100 cycles, a reversible capacity of 469.7 mA h g⁻¹ at a current density of 200 mA g⁻¹ for 300 cycles. The Coulomb efficiency was maintained at 98% except for the first cycle. After long cycling, the electrode expansion was 16%, which was much lower than those of silicon based materials. Therefore, this article provides a cheap, simple, and commercially valuable anode material for lithium batteries.

Silicon polyester (Si-PET) was synthesized with ethylene glycol and phthalic anhydride, and then it was carbonized and hydrothermally coated with glucose. The forming SiO_x with layered graphene as the 3D network had amorphous carbon layer.     

Facile in situ growth of ZnO nanosheets standing on Ni foam as binder-free anodes for lithium ion batteries

ZnO has attracted increasing attention as an anode for lithium ion batteries. However, the application of such anode materials remains restricted by their poor conductivity and large volume changes during the charge/discharge process. Herein, we report a simple hydrothermal method to synthesize ZnO nanosheets with a large surface area standing on a Ni foam framework, which is applied as a binder-free anode for lithium ion batteries. ZnO nanosheets were grown in situ on Ni foam, resulting in enhanced conductivity and enough space to buffer the volume changes of the battery. The ZnO nanosheets@Ni foam anode showed a high specific capacity (1507 mA h g⁻¹ at 0.2 A g⁻¹), good capacity retention (1292 mA h g⁻¹ after 45 cycles), and superior rate capacity, which are better than those of ZnO nanomaterial-based anodes reported previously. Moreover, other transition metal oxides, such as Fe₂O₃ and NiO were also formed in situ on Ni foam with perfect standing nanosheets structures by this hydrothermal method, confirming the universality and efficiency of this synthetic route.

ZnO nanosheets@Ni foam anode showed a high specific capacity, good capacity retention and superior rate capacity. Moreover, other transition metal oxides were also similarly formed on Ni foam, confirming the universality and efficiency of the synthetic route.     

Design and synthesis of graphene/SnO2/polyacrylamide nanocomposites as anode material for lithium-ion batteries

Tin dioxide (SnO₂) is a promising anode material for lithium-ion batteries owing to its large theoretical capacity (1494 mA h g⁻¹). However, its practical application is hindered by these problems: the low conductivity, which restricts rate performance of the electrode, and the drastic volume change (400%). In this study, we designed a novel polyacrylamide/SnO₂ nanocrystals/graphene gel (PAAm@SnO₂NC@GG) structure, in which SnO₂ nanocrystals anchored in three-dimensional graphene gel network and the polyacrylamide layers could effectively prevent the agglomeration of SnO₂ nanocrystals, presenting excellent cyclability and rate performance. A capacity retention of over 90% after 300 cycles of 376 mA h g⁻¹ was achieved at a current density of 5 A g⁻¹. In addition, a stable capacity of about 989 mA h g⁻¹ at lower current density of 0.2 A g⁻¹ was achieved.

Tin dioxide (SnO₂) is a promising anode material for lithium-ion batteries owing to its large theoretical capacity (1494 mA h g⁻¹).     

Dual-doped hierarchical porous carbon derived from biomass for advanced supercapacitors and lithium ion batteries

Nowadays, designing heteroatom-doped porous carbons from inexpensive biomass raw materials is a very attractive topic. Herein, we propose a simple approach to prepare heteroatom-doped porous carbons by using nettle leaves as the precursor and KOH as the activating agent. The nettle leaf derived porous carbons possess high specific surface area (up to 1951 m² g⁻¹), large total pore volume (up to 1.374 cm³ g⁻¹), and high content of nitrogen and oxygen heteroatom doping (up to 17.85 at% combined). The obtained carbon as an electrode for symmetric supercapacitors with an ionic liquid electrolyte can offer a superior specific capacitance of 163 F g⁻¹ at 0.5 A g⁻¹ with a capacitance retention ratio as high as 67.5% at 100 A g⁻¹, and a low capacitance loss of 8% after 10 000 cycles. Besides, the as-built supercapacitor demonstrates a high specific energy of 50 W h kg⁻¹ at a specific power of 372 W kg⁻¹, and maintains 21 W h kg⁻¹ at the high power of 40 kW kg⁻¹. Moreover, the resultant carbon as a Li-ion battery anode delivers a high reversible capacity of 1262 mA h g⁻¹ at 0.1 A g⁻¹ and 730 mA h g⁻¹ at 0.5 A g⁻¹, and maintains a high capacity of 439 mA h g⁻¹ after 500 cycles at 1 A g⁻¹. These results demonstrate that the nettle leaf derived porous carbons offer great potential as electrodes for advanced supercapacitors and lithium ion batteries.

Nettle leaf derived nitrogen and oxygen dual-doped porous carbons exhibit great potential as anodes for high performance supercapacitors and lithium ion batteries.     

Facile synthesis of Camellia oleifera shell-derived hard carbon as an anode material for lithium-ion batteries

A comparatively facile and ecofriendly process has been developed to synthesize porous carbon materials from Camellia oleifera shells. Potassium carbonate solution (K₂CO₃) impregnation is introduced to modify the functional groups on the surface of Camellia oleifera shells, which may play a role in promoting the development of pore structure during carbonization treatment. Moreover, a small amount of naturally embedded nitrogen and sulfur in the Camellia oleifera shells can also bring about the formation of pores. The Camellia oleifera shell-derived carbon has a large specific surface area of 1479 m² g⁻¹ with a total pore volume of 0.832 cm³ g⁻¹ after being carbonized at 900 °C for 1 h. Furthermore, when used as an anode for lithium-ion batteries, the sample shows superior electrochemical performance with a specific capacity of 483 mA h g⁻¹ after 100 cycles measured at 200 mA g⁻¹ current density. Surprisingly, the specific capacity is even gradually increased with cycling. In addition, this sample exhibits almost 100% retention capacity after 250 cycles at a current density of 200 mA g⁻¹.

Bio-waste Camellia oleifera shells (COS) are converted into porous carbon by a two-step method.