The present invention relates to the field of electrode materials for Sodium ion batteries. The present invention in particular relates to the pure phase hard carbon material and its method of synthesis from Rice Straw which delivered high performance as anode in Sodium-ion batteries (SIBs).
DESCRIPTION OF THE RELATED ART:
[002] In recent years, due to fossil resource shortages, development and the application of materials with carbon element are very restricted. Biomass resources such as forestry biomass, agricultural wastes, water plant, energy-source plant etc. belong to Renewable resource and become the replacement of fossil resource product. Major part of all biomass resources contains abundant carbon, therefore prepares various for raw material with reproducible biomass resource Material with carbon element the most all receives much concern.
[003] The kind of battery carbon material is a lot, typically has graphite, soft carbon, hard carbon, CNT etc., and wherein graphite is at lithium ion in battery most widely used general. But, there is specific capacity the highest (theoretical specific capacity 372mAh/g), low temperature in the application in graphite cathode Performance is the best and negative terminal surface is easily generated the problems such as Li dendrite, and graphite needs to process through high temperature graphitization to prepare, Power consumption is big, hinders the development process of associated batteries product.

[004] Hard carbon refers to be difficult to graphited carbon, is the one of amorphous carbon material. Hard carbon has the highest
reversible ratio to lithium Capacity, generally 500~1000mAh/g.
Hard carbon is with cheap, excellent cyclability and is suitable under big electric current electric discharge use Get more and more people's extensive concerning. On the other hand, the demand along with lithium ion battery increases, and the price of lithium raises, the reserves of lithium Limited grade and become lithium ion battery produce in enormous quantities, maximize obstacle. Therefore, the resourceful sodium element of use has been carried out Replace the research of the sodium-ion battery of elemental lithium.
[005] Sodium-ion battery is to utilize sodium ion embedding de-process between both positive and negative polarity to realize the secondary cell of discharge and recharge. With lithium from Sub-battery is compared, and sodium-ion battery has the advantage that sodium salt raw material rich reserves, cheap due to sodium salt characteristic, permit Permitted to use low concentration electrolyte, reduced cost; Sodium ion does not forms alloy with aluminum* and negative pole can use aluminium foil as collector, enter One step reduces cost and weight owing to sodium-ion battety is without over discharge characteristic, it is allowed to sodium-ion battery discharges into zero volt. Sodium ion Battery energy density is big, and cost advantage is obvious; but owing to the chemical property of electrode material is undesirable, sodium-ion battery develops more slow, finding suitable electrode material is one of sodium ion energy-storage battery key realizing large-scale practical application.
[006] The atomic radius of sodium ion is bigger than the atomic radius of lithium ion, is limited away from less (0.34nm) by graphite layers, Sodium ion hardly enters graphite linings. Hard carbon as

the negative material of sodium-ion battery, has a lot excellent than traditional electrode graphite Gesture. Hard carbon has loose porous and interlaced layer structure, it is possible to store substantial amounts of sodium ion, but as sodium ion negative pole the efficiency comparison first of material is low, and cycle performance is poor.
[007] Presently, agricultural waste, i.e., crop residues left in the field after harvest, has become a serious issue around the globe. India with 17.7% world population is the second largest agro-based economy where agriculture sector contributes 17-18% to the GDP and employs -50% of the total workforce available. According to a Ministry of New and Renewable Energy (MNRE) report India produces about 500 Million tons (MT) of crop residue per year. The major contributors to the crop residues are paddy straw, rice husk, sugarcane bagasse, coconut husk, jute fibres, groundnut shell, peanut shells, residues of pulses and canola crops, cotton stalk, and wastes of vegetables etc. Among these, rice straw is the largest generated crop residue (170 MT), which alone contribute 34% to the total crop residues in India. The chemical composition of rice straw mainly formed with 22% moisture, 15% lignin, 34% cellulose, 20% ash, 14% silica, 4.2% nitrogen-free extract, and the presence of less than 1% contents of each Ca, Mg, Fe, P, and S have been reported. However, there may some little variation in the chemical composition with the place/land and crop variety. Rice straw, having high contact of silica, is considered as a poor livestock feed and also does not has much local economic use. Therefore, farmers want to get rid of rice straw left in the field after harvesting as soon as possible for planting the next crop and they burn most of it "on farm". During open-field burning of rice straw 57-81% of its carbon converts to CQ2, 5-9% to CO, 0.43-0.9% to CH4 emission, while -20% of its N

converts to NO2 and -2% to N2O, and 17% as S in the rice straw transforms to SOx. In addition to these some particulate matter like elemental carbon/metal particles (PM2.5) and pollen/fine dust particles (PM10) also emit in air during in-field rice straw burning.
[008] Very recently, some serious efforts are being devoted for developing the rice straw waste management system with the objective to maximize economic benefits along with protection of the environment. One effective technology in this perspective is the conversion of Rice straw into Hard Carbon, which due to its chemical, mechanical, and structural properties demonstrates potential application as a high performance anode material for Sodium-ion batteries.
[009] Reference may be made to the following:
[010] Publication No. CN106299365 relates to a biomass hard carbon negative electrode material for a sodium ion battery, a preparing method and the sodium ion battery and belongs to the technical field of sodium ion energy storage equipment. The biomass hard carbon negative electrode material is prepared through the method including the following steps that firstly, a biomass raw material is smashed, and precursor particles are obtained; secondly, in a protection atmosphere, the precursor particles are heated to 400-600 DEG C to be pre-sintered for 1.5-2.5 h, then cooled to the room temperature along with a furnace, then heated to 800-1600 DEG C to be sintered for 2-5 h and cooled, and an intermediate is obtained; thirdly, the intermediate is put into an alkali solution to be soaked, taken out, then put into an acid solution to be soaked, then washed with water to be neutral and dried, and a purified product is obtained; fourthly, the purified product is subjected to microwave vacuum activation for 3-15 s at the power of 1000-2000

W, and then the biomass hard carbon negative electrode material is obtained. The first-time charging and discharging efficiency of the obtained biomass hard carbon negative electrode material reaches up to 90% or above, the circulation stability is good, the reversible specific capacity is 300 mAh/g or above, and the biomass hard carbon negative electrode material has a good electrochemical property.
[Oil] IN Publication No. 284/DEL/1999 relates to a process for production of mixed carbide of silicon anion (SiC- Fe3C) from fly ash which comprises heating a mixture of fly ash and carbon in an electrically conducting crucible that forms the anode employing carbon cathode and argon as plasmagen gas in a plasma reactor operating in extended arc mode at temperature 1600-2200°C in a time of 10-30 min and recovering SiC-Fe3C by conventional leaching methods.
[012] IN Publication No. 393/DEL/2006 relates to a method and an equipment for the production of fine and ultrafine powders by in flight processing of various electrically conducting and non¬conducting precursor materials such as metals, alloys, composites, ceramics like coarse SiC and electrically non-conducting powder such as charred rice husk, in thermal plasma, utilizing a combination of both non-transferred as well as transferred plasma arc mode.
[013] IN Publication No. 201611034531 relates to a process of preparing a wood derived carbon - metal oxide (C - MOx) composite material where M is a metal like Titanium, Tin, Silicon, Magnesium, and Bismuth* They aire prepared by nano casting of wood templates with respective metal oxide or metal iso-propoxide like LTO, Ti02, Sn02, MgO, Si02, Bi203, LNMC, LNMA, and LiCo02 dissolved in

Ethyl Alcohol / IPA / water solution. Electrochemical studies revealed that resultant product has a capacity in the range 150mAh/g to 1500mAh/g, excellent coulomb efficiency of 98 -100%, cycle stability for 10 - 1000 cycles and rate capability from current density of lOOmA/g to 10 A/g, when used as electrode material in Lithium ion batteries and super capacitors.
[014] Publication No. CN105655590 relates to a method for preparing a spherical lithium/sodium battery negative electrode carbon material. The method includes the steps that raw materials are washed, crushed and then dried; the dried raw materials are soaked in a salpeter solution, after the mixture is stirred, a hydrothermal reaction is conducted for 12-24 hours at the temperature of 120-180 DEG C, then the mixture is cooled to the room temperature along with a furnace, and a product is obtained; the product is placed into a porcelain boat and carbonized in an atmosphere oven, then the temperature is raised to 500-1,000 DEG C under a protection atmosphere, heat preservation is conducted for 2-5 hours, then purification is conducted through a KOH solution and a hydrochloric acid solution, and the spherical lithium/sodium battery negative electrode carbon material is obtained. A lithium/sodium ion battery assembled by the carbon material prepared through the method can represent high cycle performance under the high current density, and irreversible de-intercalation of work ions of the battery under a large current is greatly prolonged, so that the service life of the battery is prolonged, and by the adoption of the method, the raw material source is wide, the preparation process is simple, and industrialization ifc easy to realize.

[015] Patent No. US10495599 relates to a nano structured material that comprises pyrolyzed date palm leaves that are obtained from a pyrolysis of an agro-waste containing date palm leaves in an inert gas and in a temperature range of 800 to 1600° C, an electrochemical cell thereof, and a method of determining a hydroquinone concentration in a hydroquinone-containing solution with the electrochemical cell.
[016] Publication No. CN101037200 relates to a method of preparing active carbon material used for organic super capacitor from straw, which is characterized in that the active carbon material used for organic super capacitor is obtained by the processing steps of drying, smashing, carbonizing and activation, using crop straw as raw material. The active carbon of the present invention has a big specific surface area, and a specific capacitance of 232 F/g at 2 mv/s which is tested by circular volt-ampere test using an electrolyte of MeEt3NBF4/AN having a concentration of 1.2 mol/1, and is qualified as electrode material of organic super capacitor.
[Olt] Publication No. CN104779065 relates to a straw-based super capacitor electrode with high volumetric specific capacitance. The electrode is characterized by being prepared from raw materials in parts by weight as follows: 100-120 parts of a modified straw composite material, 3-5 parts of lithium titanate, 1-2 parts of chitosan, 2-3 parts of polyethyletie glycol imine, 1-2 parts of tourmaline powder, 1-3 parts of expanded vermiculite powder, 1-2 parts of a binder LA 132 and a proper amount of deionized water. Carbon with the high activity and the high specific surface area is prepared through carbonization, activation and doping modification of crop straw, the added polyethylene glycol imine and lithium titanate have good electrical conductivity, the prepared super

capacitor electrode is excellent in charge and discharge stability and high in specific capacitance, specific power and specific energy value.
[018] The article entitled "Hierarchical porous carbon derived from rice straw for lithium ion batteries with high-rate performance" by Feng Zhang; Kaixue Wang; Guo-Dong Li; Jiesheng Chen; Electrochemistry Communications 11(1):130-133; January 2009 talks about the porous carbons with a high surface area have been prepared from rice straw. The hierarchical porous network with large macroporous channels and micropores within the channel walls enable the porous carbons to provide the pathways for easy accessibility of electrolytes and fast transportation pf lithium ions. These porous carbons which show a particular large reversible capacity are proved to be promising anode materials for high-rate and high-capacity lithium ion batteries.
[019] The article entitled "Rice husk-derived carbon anodes for lithium ion batteries" by Liping Wang, Zoe Schnepp and Maria MagdalenaTitirici; Journal of Materials Chemistry A, issue 17; 2013 talks about the carbon fibers were obtained using hydrothermal carbonization of rice husk followed by further heat treatment at 1000 °C to increase the conductivity and removal of the silica fraction to increase the porosity. These carbon fibers show superior capacity retention and rate performance as anode in lithium ion batteries.
[020] The article entitled "The conversion of biomass into carbon electrode material using FeC13 as an activating agent for battery application" by E Andrijanto, I Purwaningsih, L Silvia, G Subiyanto and M Hulupi; Earth and Environmental Science 299 012001; 2019 talks about the batteries and supercapacitors are one of the energy

storage devices that had been used for a practical application most electronic devices such as mobile phone. The development of these energy storage devices is faced by the poor performance of (the) electrode. Electrode commonly used for batteries and supercapacitors is derived from nonrenewable carbon resources such as graphite. However, the availability of this material is becoming a long-term problem for the development of batteries and supercapacitors. Biomass from (the) waste plant as a green source for battery electrode is one of alternative carbon which has great potential, due to the low price, easy to process and has high stability. This paper reports the study of the biomass conversion into carbon electrode material having high electrical conductivity or low electrical resistivity using carbonization and pyrolysis process. The process involved FeC13 as an activating agent to reduce the elqctrical resistivity of the material as low as possible. The research was studying the effect of biomass sources and the processing method on the electrical resistivity of the electrode produced. The biomasses used in the study were corncob, water hyacinth, rice straw, and coconut husk. The material is the waste plant which is available in abundant. The morphological analysis of the carbon surface was conducted using Scanning Electron Microscope-Energy Dispersive X-Ray (SEM-EDX).
[021] The article entitled "Biomass-derived activated porous carbon from rice straw for a high-energy symmetric supercapacitor in aqueous and non-aqueous electrolytes" by N. Sudhan, K. Subramani, M. Karnan, N. Ilayarajaand M. Sathish; Energy Fuels 2017, 31, 1, 977-985; December 7, 2016 talks about the biomass-derived activated carbon materials prepared by a two-step synthesis via carbonization followed by KOH activation of rice straw at 600 °C in an argon atmosphere. The formation of disordered micro- and

mesopores on carbon by KOH chemical activation and the high specific surface area of -1007 m2 g-1 were confirmed by N2 adsorption-desorption. Further, the scanning electron microscopic analysis revealed the formation of disordered pores over the carbon surface, and the transmission electron microscopic analysis confirmed the formation and aggregation of ultrafine carbon nanoparticles of —5 nm in size after the carbonization and activation processes. The three-electrode cell in aqueous electrolyte shows high specific capacitance of 332 F g-1, with high specific capacitance retention of 99% after 5000 cycles. The fabricated symmetric supercapacitor device in aqueous 1 M H2SO4 electrolyte showed a high specific capacitance of 156 F g-1, with a high energy density of 7.8 Wh kg-1. The symmetric device fabricated using l-ethyl-3-methyl imidazolium tetrafluoroborate ([EMIM] [BF4] ) ionic liquid exhibited a cell voltage of 2.5 V and a specific capacitance of 80 F g1, with a high energy density of 17.4 Wh kg-1.
[022] The observed electrochemical performance clearly indicates that activated carbon derived from rice straw could be used as a promising electrode material in a supercapacitor for electrochemical energy storage. The cheaper and readily available rice straw raw materials, simple chemical activation process, and high performance promise that the obtained carbon material is viable for commercial applications in supercapacitors.
[023] The article entitled "Engineering rice husk into a high-performance electrode material through an ecofriendly process and assessing its application for lithium-ion sulfur batteries" by Sheng-Siang Huang, Mai Thanh Tung, Chinh Dang Huynh, Bing-Joe Hwang, Peter Maria Bieker, Chia-Chen Fang, and Nae-Lih Wu; ACS Sustainable Chem. Eng. 2019, 7, 8, 7851-7861; March 8, 2019 talks

about the high-capacity and cycle-stable SiOx/C composite anodes for Li-ion batteries (LIBs) synthesized from rice husk (RH) using an ecofriendly, one-step pyrolysis process that takes full advantage of both the silica and organic components of RH. The process-property-performance relationship for this process was investigated. Pyrolysis of RH at a sufficiently high temperature (1000 °C) results in a C scaffold with a low surface area, high electronic conductivity, and embedded SiOx nanoparticles that are highly active toward lithiation, enabling high rate capability along with outstanding cycle stability for LIB applications. A SiOx/C anode delivering a specific capacity of 654 mAh g-1 and retaining 88% capacity (99.8% CE) after 1000 cycles was demonstrated. Higher capacities, up to 920 mAh g-1, can be achieved by adding a Si-containing polymer coating on RH prior to pyrolysis. The SiOx/C anodes demonstrated considerable promise for Li metal-free Li-ion sulfur batteries.
[024] The prior art refer to the use of Rice Straw as biomass precursor in electrode materials for lithium ion batteries and super capacitors. IVtoreover, the prior cited arts, listed above, mentioned use of other biomass precursors like rice husk or wood to synthesize carbon electrode material for lithium-ion/sodium-ion batteries and super capacitors. However, Rice straw has never been explored as biomass precursor in electrode material for Sodium ion batteries.
[025] In order to overcome above listed prior art present invention provides a tiovel process to synthesize high performance pure-phase Hard Carbon anode material for SIBs using Rice Straw as biomass precursor. The process includes acid soaking pre-treatment steps on Rice straw which removes all metallic and other inorganic impurities from the precursor material. This leads to the synthesis of pure-

phase hard carbon material, which delivers high performance as anode in SIBs. The use of acid soaking pre-treatment on Rice straw to synthesize high performance pure-phase hard carbon material for SIBs.
OBJECTS OF THE INVENTION:
[026] The principal object of the present invention is to provide rice straw derived pure-phase hard carbon anode material for sodium-ion batteries (SIB).
[027] Another object of the present invention is to provide the method of synthesis of high performance Sodium ion battery (SIB) anode material using rice straw as biomass precursor.
[028] Yet another object of the present invention is to provide synthesis of low cost and high performance hard carbon anode material for sodium-ion batteries.
SUMMARY OF THE INVENTION:
[029] The present invention relates to the electrode materials for Sodium ion batteries. Rice straw derived pure-phase hard carbon material has been synthesized as a high performance anode material for Sodium-ion batteries (SIBs). The invention led to the synthesis of pure phase hard carbon material which delivered high performance as anode in sodium-ion batteries. The preparation method to synthesize hard carbon is facile and industrially scalable.
[030] The method involves following preparation steps: Cutting the biomass precursor into small pieces followed by washing it thoroughly in de-ionized water (D.I. water); the washed material was then dried in oven followed by grinding below 300 microns; the grounded material was then soaked in hydrochloric acid solution

(HC1) and was washed thoroughly with D.I. water; the material was again soaked in hydrofluoric acid solution (HF) followed by washing with D.I. water; the washed material was then dried in vacuum conditions followed by high temperature treatment involving multi-step controlled environment and-heating/cooling processes. Thus, the invention provides synthesis of low cost and high performance hard carbon anode material for Sodium-ion batteries.
BREIF DESCRIPTION OF THE INVENTION
[031] It is to be noted, howeVer, that the appended drawings illustrate only typical embodiments of this invention and are therefore hot to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments.
[032] Figure 1 shows schematic for synthesizing Hard Carbon from Rice Straw;
[033] Figure 2 shows multi-step heating process of rice-straw derived hard carbon;
[034] Figure 3 shows (a) XRD pattern of RS-1200sample, and (b) FE-SEM micrograph;
[035] Figure 4(a) shows specific capacity vs voltage plot for RS-950, RS-1100 and RS-1200 at 0.1 C in a potential range of 0.005-1.0 V (vs. Na/Na+);
[036] Figure 5 shows specific capacity vs heating rate for RS-1200 at 0.1 C in a potential range of 0.005-1.0 V (vs. Na/Na+);
[037] Figure 6 shows specific capacity vs acid concentrations for RS-1200 at 0.1 C in a potential range of 0.005-1.0 V (vs. Na/Na+).
DETAILED DESCRIPTION OF THE INVENTION:

[038] The present invention provides high performance sodium ion battery (SIB) anode material using rice straw and its method of synthesis. Rice straw derived pure-phase hard carbon material has been synthesized as a high performance anode material for Sodium-ion batteries (SIBs).
[039] The invention led to the synthesis of pure phase hard carbon material which delivered high performance as anode in sodium-ion batteries. The preparation method to synthesize hard carbon is facile and industrially scalable.
[040] The invention is described in detail with reference to the examples given below. The examples are provided just to illustrate the invention and therefore, should not be construed to limit the scope of the invention.
[041] EXAMPLES
[042] Example 1
[043] Synthesis of Rice Straw Derived Hard Carbon
[044] Rice Straw was obtained from a village near Roorkee, India. It was cut into small pieces and then washed thoroughly using de-ionized water (D.I. water). The washed pieces were then dried completely in a hot air oven and then grounded into powered form (particle size between 100 to 300 microns). 2.5 g of the powdered rice straw material was soaked with 6.0M hydrochloric acid (HC1) solution for 6 h and then washed thoroughly with D.I. water till pH reached to 7. The obtained material was again soaked in 5.0 M hydrofluoric acid (HF) solution for 6h and washed with D.L water till pH became 7. The washed material was then dried overnight under vacuum conditions at 80°C. 1 g of dried material is then calcined at

atmospheric pressure via multi-step heating process under argon environment at 1200°C for 5 h in a tubular furnace. It was then naturally cooled to room temperature under inert environment. The multi-step heating follows first heating the material up to 350°C in 2h 30 min followed by heating at 350°C for 3 h. The third step heating process involves heating the material up to 600°C from 350°C in 1 h followed by heating at 600°C for 2 h. The fifth step (final) heating process involves heating the material up to the reaction temperature 1200°C from 600°Cat ramping rate of 3°C/min. After completion the process, furnace was allowed to cool down naturally. The complete synthesis procedure and multi-step heating process of rice-straw derived hard carbon are shown in Fig. 1 and Fig. 2, respectively. The Hard Carbon (HC) material carbonized at 950°C, 1100°C, and 1200°C are labeled as RS-950, RS-1100, and RS-1200, respectively.
[045] The essential characterization techniques such as X-Ray Diffractometer (XRD, Rigaku SmartLab SE using CuKa 1.5406 A radiation) and Field Emission Scanning Electron Microscope (FE-SEM, Carl Zeiss Ultra Plus) equipped with Energy Dispersive X-Ray Spectroscopy (X-Max, HORIBA were utilized to know the crystal structures, surface morphology and elemental analysis of the synthesized rice-straw derived hard carbon.
[046] Fig. 3(a) demonstrates the X-Ray Diffraction (XRD) patterns of the rice-straw derived hard carbon (RS-1200). No impurity peak is observed in the XRD pattern which implies that acidic treatment process of rice-straw has removed the possible metallic impurities existing in it. The XRD pattern represents some amorphous peaks at 20 angles of 22.86°, 43.7°, and 79.4° which are corresponding to (002), (100), and (110) peaks of hard carbon, respectively (Fig. 3a).

The appearance of broadened peaks (hump) in the XRD pattern represents disorderedness/ defects in the carbon structure. After carbonization at 1200 °C, the overall yield of the synthesis process was around 13-14%. Fig.3 (b) is the FE-SEM micrograph of the synthesized hard carbon. Here presence of pores in the sample can be seen clearly.
[047] Example 2
[048] Electrode Preparation and Cell Assembly [Sodium ion battery):
[049] In order to investigate the sodium-ion storage performance of the rice-straw derived hard carbon, electrodes were prepared via uniformly mixing the hard carbon powder with acetylene black (Timcal) and water soluble sodium Carboxy-methyl-cellulose (CMC) (Sigma Aldrich) binder in a weight ratio of 70:15:15. This mixture was stirred for 12 h and the obtained ink like homogeneous slurry was uniformly coated onto the Al foil via doctor blade technique, and dried at 80 °C in an air oven for 12h. After that, coated Al foil was passed through the calendaring machine to improve the adhesion of active materials to the Al foil. Then for the 2016-type coip cells fabrication, the electrodes were cut into a diameter of 16 mm from the coated Al foil, having mass loading of 2-2.5 mg cm-2.1 These electrodes were dried at 70 °C for 6 h and then transferred to an argon-filled glove box (M-Brawn, Germany) maintaining the content of H20 and 02 less than 0.5 ppm in the box. The Na cells (CR2016) were assembled in an argon-filled glove box using Sodium metal (Sigma Aldrich), 1.0 M NaC104 in EC: DEC (1:1 v/v) (Sigma Aldrich), and glass fiber filter (Macflow) as a counter electrode, electrolyte solution and separator, respectively. For cell fabrication, first working electrode was positioned at the center of the coin/cup to form the positive terminal of the cell then a glass fiber filter, which

is permeable to the Na-ions but impermeable to material particles and electrons, was placed over it. After that a circular piece of Na-metal (-16 mm diameter) was centrally placed on the separator followed by a steel spring. This forms the negative terminal of the cell. Finally, this arrangement was mechanically pressed using crimping machine (MTI corp.) to form half Na-cell.
[050] Electrochemical characterization (Sodium ion battery):
[051] The galvanostatic charge-discharge cycling (GCD) analysis of the designed cell were performed at -25 °C using battery analyzer (MTI Corp. USA, BST8-WA in the voltage range of 0.005-1.0 V at current rate of 25 rtiA g-1.
[052] Electrochemical Performance (Sodium storage properties):
[053] The energy storage performance of rice-straw derived hard carbon electrodes were examined in Na cells and the results are shown in Fig. 4. Table 1 shows the initial reversible capacity values for the hard carbon electrodes in Na cells. The hard catbon prepared at 950°C, 1100°C, and 1200°C showed the initial reversible capacities of 166mAh g-1, 236mAh g-1, and 273 mAh g-1, respectively, as shown in Table 1. The hard carbon samples processed at 1200 °C delivered the highest initial reversible capacity of 273 mAh g-1 with Coulombic efficiency of 100%, justifying the processed condition of synthesized HC from Rice Straw as a prospective negative electrode material for sodium ion batteries.
Table 1

RS-HC Processed at
Different
Temperatures Initial Reversible Capacity (mAh g-1) Plateau Capacity
(mAh g-1) (0.005 V-0.2 V)

950 °C 166 (±5) 51 (±5)
1100 °C 236(±5) 126 (±5)
1200 °C 273 (±5) 160 (±5)
[054] Example 3
[055] Effect of Heating Rate
[056] In order to analysis the effect of heating rate/ramping rate on the energy storage performance of the synthesized material, hard carbon electrode material was prepared using Method discussed above. In it, the ramping rate before final heating step was tested for 2°C/min, 3°C/min and 5°C/min and the corresponding samples are labeled as 2D, 3D, and 5D, respectively.
[057] The energy storage performance of electrodes was examined in Na cells. Figure 5 shows the initial reversible capacity and plateau capacity (0.005 V-0.2 V) values for the hard carbon electrodes in Na cells. The hard carbon prepared for 2D, 3D and 5D samples showed initial reversible capacities of 234mAh g-1, 273mAh g-1, and 239 mAh g-1, respectively. The hard carbon samples processed for 3D sample delivered the highest initial reversible capacity and plateau capacity of 273 mAh g-1 and 160 mAh g-1 respectively, showing influence of heating/rathping rate on synthesized hard carbon from rice straw as a prospective negative electrode material for Sodium ion batteries.
[058] Example 4
[059] Effect of Acid concentration

[060] In order to analyze the effect of acid concentration on the energy storage performance of the synthesized material, hard carbon electrode material was prepared using method discussed above. In it, the concentration of hydrofluoric acid (HF) solution was kept constant while concentration of hydrochloric acid (HC1) solution varied in following way: 2 M, 3 M and 6 M. The samples were labeled as 3DA, 3DB and 3DC, respectively.
[061] The energy storage performance of electrodes was examined in Na cells. Fig.6 shows the initial reversible capacity and plateau capacity (0.005 V-0.2 V) values for the hard carbon electrodes in Na cells. The hard carbon prepared for 3DA, 3DB and 3DC sample showed initial reversible capacities of 247mAh g-1, 248mAh g-1, and 273 mAh g-1, respectively. The hard carbon samples processed for 3DC sample delivered the highest initial reversible capacity and plateau capacity of 273 mAh g-1 and 160 mAh g-1 respectively, showing influence of acid solution concentration on synthesized hard carbon from rice straw as a prospective negative electrode material for Sodium ion batteries.
[062] Further, Fig. 5 & 6 demonstrate that heating rate and the concentration of acids, used in the synthesis procedure, greatly influence the specific capacity as well as plateau capacity of the synthesized Rice Straw derived hard carbon.
[063] Here, the unique morphology of the starting precursor (raw material), the temperature control in terms of heating rate, and concentration of acids in present synthesis conditions effectively govern the overall energy storage performance of Rice Straw derived hard carbon as shown in Figures 4, 5 and 6.

[064] Numerous modifications and adaptations of the system of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and Adaptations which Call within the true spirit and scope of this invention.

WE CLAIM:
1. A sodium ion battery (SIB) anode material using rice straw comprises pure phase hard carbon material and its method of synthesis includes following steps:
a. Cutting the biomass precursor into small pieces followed by
washing it thoroughly in distilled water;
b. the washed material was then dried in oven at a temperature
in the range of 50°C to 80°C
c. grinding the material obtained in the range of mesh size
between 100 to 300 microns;
d. the grounded material was then soaked single/multiple
times in acid solutions selected from the hydrofluoric acid
(HF), nitric acid (HNO3), sulfuric acid (H2SO4) or hydrochloric
acid (HC1) wherein molar concentration of the acid solutions
is kept between 0.1 M to 10.0 M and soaking time is between
1 h to 24 h, at a temperature between 25°C to 100°C;
e. Wash the material obtained thoroughly with distilled water
till pH become close to 7;
f. Dry the material obtained under vacuum and at temperature
between 50°C to 100°C;
g. High temperature treatment of material obtained, involving
intermittent heating/cooling profile under controlled-
environment (N2 or Argon gas or Ar/H2 gas mixture) in the
temperature range of 600°C to 1500°C for 0.5 h to 12 h;

2. The sodium ion battery (SIB) anode material as claimed in claim 1 wherein the composite electrode for Sodium ion battery consists of synthesized rice-straw derived hard carbon material, binder and Super-P (carbon black) in weight percentage of (80 ± a): (10 ± b): (10 ± c), respectively, where the a, b, and c can attain values between 0 to 20 in a manner that proportional percentage sum of rice straw derived - hard carbon material, binder and Super-P remains hundred.
3. An electrode (anode) material for rechargeable metal ion batteries prepared by the method as claimed in claim 1 wherein the rechargeable metal-ion batteries are selected from lithium-ion battery, sodium ion battery, potassium ion battery, magnesium ion battery or calcium ion battery.
4. The sodium ion battery (SIB) anode material prepared by the method as claimed in claim 1 wherein the acid solution concentration in the range of 1.0 M-7.0 M has found beneficial to increase plateau capacity (from 0.005 V-0.2 V) towards high performance anode material for Sodium ion battery.
5. The sodium ion battery (SIB) anode material prepared by the method as claimed in claim 1 wherein, the heating temperature in the range of 900°C-1500°C and/or ramping rate in the range of l°C/min-10°C/min also exhibited beneficial effect to increase plateau capacity (from 0.005 V- 0.2 V) towards high performance anode material for Sodium ion battery.