DESC:FIELD OF INVENTION:
[0001] The present invention relates to a phenolic resin based hard carbon-graphite composite as an anode material for energy devices and the process of preparation thereof. More particularly, the present invention relates to the phenolic resin based hard carbon-graphite composite as an anode material and its use as a high-capacity anode material.

BACKGROUND:
[0002] The advancement of clean and eco-friendly energy has drawn worldwide attention, based on the rising energy and environmental issues. To address the issue apart from other alternative resources like solar, wind and so on, lithium-ion batteries (LIBs) dominate the market due to the following characteristics like high energy and power density, high voltage, long lifespan, and pollution-free operation options. Also, with extensive usage in portable electronic devices, hybrid electric vehicles (HEVs), and electric vehicles (EVs) it has gained much importance. Nevertheless, with the considerable rise in the energy storage demand, lithium consumption has increased, and with the uneven geographical distribution and the limited lithium resources, there is an earnest need to develop an alternative energy storage technology that could fill for LIBs.

[0003] Nowadays other types of secondary batteries, like Sodium ion and Potassium ion batteries, which has identical working principle with Li ion batteries, have been proposed as promising next-generation energy storage technology because of the evident advantages of the low-cost and worldwide abundance of charge carriers. Besides, the cost of these secondary batteries could be further reduced by the use of an aluminum current collector on the anode side since sodium does not alloy with aluminum. In addition to the commercial benefits, sodium-ion batteries offer a potentially safe way for batteries storage and transportation.

[0004] An efficient anode material is a crucial factor that governs the future success of secondary batteries like sodium and potassium ion batteries. Based on the reaction mechanisms, there are three classes of anodes materials: insertion based, conversion based, and alloying based.

[0005] Carbon-based materials have been explored by researchers and scientists over the past few decades as electrode materials for energy storage applications like secondary batteries (i.e. Li-ion, Sodium-ion, Potassium-ion), super capacitors, fuel cells, and so on. They have attracted more attention due to their low-cost, high structural stability, and good electrical conductivity. The hard carbons produced from various polymers and biomasses with a relatively high disordered degree and large interlayer distance are favorable for Secondary batteries. However, hard carbon has a highly disordered structure and a low degree of graphitization which leads to diminished electrical conductivity, and poor rate performance. In addition, the low initial coulombic efficiency (ICE) also affects the energy density in the fuel cell configuration.

[0006] There are however various patent and non-patent literatures that report hard carbon based anode materials. They are as follows:

[0007] Ning Sun et al. “Facile synthesis of high-performance hard carbon anode materials for sodium-ion batteries” report the facile synthesis of a biomass-derived hard carbon for SIBs by one-step pyrolysis of shaddock peel under inert atmosphere. They achieved high reversible sodium storage capacities up to 430.5 mAhg-1 at a current density of 30 mAg-1 and superior cycling stability with only 2.5 % capacity loss over 200 charge-discharge cycles.

[0008] H.D. Asfaw et al “Facile synthesis of hard carbon microspheres from polyphenols for sodium-ion batteries: insight into local structure and interfacial kinetics” proposed to synthesize hard carbon microspheres (CMSs) from resorcinol-formaldehyde precursors produced via an acid-catalyzed polycondensation reaction. Electrochemical tests indicated that the HC synthesized at 1500oC showed the best performance with an ICE of 85-89% and a reversible capacity of 300-340 mAhg-1 at 10 mAhg-1, with most of the charge stored below 0.1 V.

[0009] Qingyin Zhang et al “Hard carbon microspheres derived from resorcinol formaldehyde resin as high-performance anode materials for sodium-ion battery” reported a reversible specific capacity of 321 mAhg-1 and high initial Coulomb efficiency of 82% at the current rate of 0.1 C using microsphere of hard carbon derived from resorcinol formaldehyde resin.

[0010] Huimin Zhang et al “Coupled Carbonization Strategy toward Advanced Hard Carbon for High-Energy Sodium-Ion Battery”adopted a new coupled carbonization strategy to prepare a cost-effective hard carbon material by pyrolyzing and carbonizing the mixture of abundant sucrose and phenolic resin. The hard carbon has a higher capacity of 319 mAhg-1 and capacity retention of 90% over 150 cycles.

[0011] He-liang Wang et al “Properties and sodium insertion behavior of Phenolic Resin-based hard carbon microspheres obtained by a hydrothermal method” claimedhigh reversible capacity of 311 mAhg-1 and good long-term electrochemical stability when the sample is prepared at 1250 °C.

[0012] Azusa Kamiyama et al, “High-Capacity Hard Carbon Synthesized from Macroporous Phenolic Resin for Sodium- and Potassium-Ion Battery”studied the influences of temperatures on the structures and electrode properties of the hard carbon in Na and K cells. They observed that hard carbon carbonized at 1500 ºC delivers the largest capacities of 386 and 336 mAhg-1 at 10 mAg-1 in Na and K cells.

[0013] Zheng Wei et al “Insights into the pre-oxidation process of phenolic resin-based hard carbon for sodiumstorage”synthesized a hard carbon material from phenolic resin and manipulated its microstructure by tuning the pyrolysis temperature and pre-oxidation procedure.

[0014] Shuo Wang et al, “Phenolic Resin-based Carbon Microspheres for Potassium Ion Storage” reported the synthesis of hard carbon using phenolic resin and thereby using it as an anode material for potassium ion battery. They achieved a reversible capacity of241mAh/gm at a current density of 25mA/gm.

[0015] CN106935856B titled “Sodium-ion battery carbon-based composite negative electrode material and preparation method thereof” discloses a preparation method of a sodium-ion battery carbon-based composite anode material. The aforesaid patent also discloses a sodium-ion battery carbon-based composite negative electrode material prepared using phenolic resin, which comprises hard carbon spheres and graphitized carbon materials adsorbed and/or coated on the surfaces of the hard carbon spheres. The cell of the aforementioned patent reference shows a profile for charge-discharge specific capacity (in mAh/g) over a few limited cycles.

[0016] CN115010109B titled “Preparation method of phenolic epoxy resin-based hard carbon material, hard carbon material and sodium ion battery” discusses about a preparation method of a phenolic epoxy resin-based hard carbon anode material.

[0017] CN114373924A titled “Green phenolic resin-based hard carbon negative electrode material for lithium/sodium ion battery and preparation method thereof” discusses about a green phenolic resin-based hard carbon negative electrode material for a lithium/sodium ion battery and a method thereof.

[0018] List of abbreviations:
EMC: Ethyl Methyl Carbonate
PC: Propylene Carbonate
FEC: Fluoroethylene Carbonate
PP: Polypropylene
DTD: Dithiane Diol
PST: prop-1-ene-1, 3-sultone
HC: Hard Carbon

OBJECTS OF INVENTION:
[0019] It is the object of the present invention to provide an anode active material (or an anode composite material) that improves the cyclic properties of secondary batteries.

[0020] Yet another object of the invention is to provide a graphite incorporated phenolic resin-based hard carbon as an anode active material for ion-batteries that exhibit enhanced stability.

SUMMARY OF INVENTION:
[0021] In an aspect, the present invention provides a phenolic resin based hard carbon - graphite composite as an anode material for energy devices.

[0022] Another aspect of the present invention is to provide a two-step synthesis of the phenolic resin based hard carbon - graphite composite that is simple, reliable, cost-effective, especially on a commercial scale, and uses readily available starting precursors that do not require complex handling conditions and produces the said composite in good yields.

[0023] In an aspect, the present invention provides a phenolic resin based carbon-graphite composite as anode material comprising phenol and formaldehyde in a ratio ranging from 1:1 to 1:5 along with graphite in an amount ranging between 0.1 - 20 wt% of the phenol.
[0024] The ratio of phenol and formaldehyde is the molar ratio of phenol and formaldehyde in the range of 1:1 to 1:5.

[0025] In an aspect, the preferred graphite concentration is 10wt% of the phenol or 5 wt% of the phenol.

[0026] Yet in another aspect of the present invention, the present invention provides a method for synthesizing a composite material for an anode electrode, the method comprising steps of:
a) preparing a thermosetting phenolic resin solution by mixing phenol and formaldehyde under an alkaline solution in a ratio ranging from 1:1 to 1:5;
b) mixing graphite with the thermosetting phenolic resin solution in a predetermined quantity to obtain a precursor mixture;
c) performing a hydrothermal reaction on the precursor mixture obtained from step (b) to yield a polymerized phenolic resin;
d) crushing the polymerized phenolic resin obtained from step (c) into a fine uniform powder; and
e) pyrolyzing said powder obtained from step (d) at a high temperature to yield the composite material for the anode electrode.

[0027] In an aspect, the ratio of phenol and formaldehyde is the molar ratio of phenol and formaldehyde in the range of 1:1 to 1:5.

[0028] In an aspect, the ratio of phenol and formaldehyde in the thermosetting phenolic resin solution is 1:2.5 by volume or 1:1 by molar ratio.

[0029] In an aspect, the ratio of phenol and formaldehyde is 1:2.5, preferably 1:1.25 by molar ratio.

[0030] In an aspect, the preferred graphite concentration is 10wt% of the phenol or 5 wt% of the phenol.
[0031] In another aspect, the present invention provides an electrochemical cell comprising:
a cathode electrode comprising a layered transition metal oxide;
an anode electrode comprising a phenolic resin based hard carbon-graphite composite comprising of phenol and formaldehyde in a ratio ranging from 1:1 to 1:5 along with graphite in an amount ranging between 0.1 - 20 wt% of the phenol;
a separator; and
an electrolyte.

[0032] In an aspect, the ratio of phenol and formaldehyde is the molar ratio of phenol and formaldehyde in the range of 1:1 to 1:5.

[0033] In an aspect, the electrolyte comprises of an alkali salt dissolved in an organic solvent with an additive. The alkali salt may be selected from NaPF6, NaClO4, LiPF6 or KPF6. The organic solvent may be selected from Di-ethyl carbonate, Di-methyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene carbonate and the like. The additive may be any inorganic and/or organic electrolytic additive like fluorinated ethylene carbonate (FEC), and the like which is widely known and appreciated in the art. Further, the electrolyte comprises of 0.8M NaPF6-PC: EMC: 2%FEC: 1%PST:1% DTD.

[0034] In yet another aspect, the composite prepared as anode active material, enables its direct use without any further separation or purification steps.

[0035] Accordingly, the present invention provides an electrochemical cell comprising:
1) A layered transition metal oxide-based cathode material;
2) A phenolic resin based hard carbon - graphite composite anode material;
3) A separator between the anode and cathode; and
4) An electrolyte.

[0036] In an aspect, the present invention provides the use of the anode active material as an anode with in conjunction with counter electrode and an electrolyte in the energy device.

[0037] In an aspect, the said anode material is used in secondary batteries like lithium-ion batteries, more particularly, Sodium-ion or potassium ion batteries that can deliver an excellent first discharge capacity and exhibit high initial columbic efficiency.

BRIEF DESCRIPTION OF DRAWINGS:
[0038] Despite the prior arts addressing phenolic resin-based hard carbon anode material, the present invention envisages a novel phenolic resin based hard carbon-graphite composite for use as an anode active material in secondary batteries or alkali-metal ion batteries or Lithium, Sodium, or Potassium ion batteries that can improve the cyclic properties of secondary batteries substantially as compared to the known phenolic resin-based hard carbon anode material.

[0039] Figure 1 illustrates a cell voltage profile for the first charge and discharge of the phenolic based hard carbon and 5% graphite composite in a half cell format using 0.8M NaPF6-PC: EMC: 2%FEC: 1%PST: 1% DTD as electrolyte.

[0040] Figure 2 illustrates a discharge fading ratio of the half-cell made using phenolic-based hard carbon and 5% graphite composite in a half cell format using 0.8M NaPF6-PC: EMC: 2%FEC: 1%PST: 1% DTD as electrolyte for the first 50 cycles.

[0041] Figure 3 illustrates the cyclic performance (or capacity retention) of the half-cell having an anode made from the present phenolic resin based hard carbon - graphite composite material.

DETAILED DESCRIPTION OF INVENTION:
[0042] Hereinafter, various aspects and embodiments of the present disclosure will be explained in more detail; however, this is not intended to limit the scope of the present invention.

[0043] Throughout the disclosure, the term “cycle” for a cell may be interpreted as a cycle comprising a charging activity followed by a discharging activity for a given cycling process.

[0044] The composite material for anode in the present invention is made from hard carbon and graphite along with phenolic resin. The hard carbon is primarily an unstructured form of carbon. The microscopic structure of the hard carbon can vary significantly depending on the precursor material. The resin-based hard carbon is well-known in the art; however modifications to the synthesis can have a substantial impact on the composite material which affects the anode’s performance. In the present invention, the addition of graphite serves as a structure-directing agent during the carbonization process. This enhanced structural refinement leads to improved cycle life and overall performance of the battery having anode made from the phenolic resin based hard carbon-graphite composite. The aforesaid synthesis of the anode composite material is explained in the subsequent paragraph.

[0045] In an embodiment, the present invention discloses a novel phenolic resin based hard carbon - graphite composite as an anode active material with an excellent first discharge capacity and high initial columbic efficiency for energy devices such as secondary batteries like lithium-ion batteries, more particularly, Sodium-ion or potassium ion batteries.

[0046] In an embodiment, the present invention provides an active material for anode electrode comprising phenol and formaldehyde in a ratio ranging from 1:1 to 1:5 along with graphite wherein the graphite percentage varies from 0.1 - 20 wt%. In an embodiment, the ratio of phenol and formaldehyde is the molar ratio of phenol and formaldehyde in the range of 1:1 to 1:5. In an alternate embodiment, the ratio between phenol and formaldehyde is 1:2.5 or preferably 1:1.25 by molar ratio. Further, the preferred graphite concentration is 10 wt% of the phenol or 5 wt% of the phenol.

[0047] Yet in another embodiment of the present invention, a method for synthesizing a composite material for an anode electrode, the method comprising steps of:
a) preparing a thermosetting phenolic resin solution by mixing phenol and formaldehyde under an alkaline solution in a ratio ranging from 1:1 to 1:5;
b) mixing graphite with the thermosetting phenolic resin solution in a predetermined quantity to obtain a precursor mixture;
c) performing a hydrothermal reaction on the precursor mixture obtained from step (a) to yield a polymerized phenolic resin;
d) crushing the polymerized phenolic resin obtained from step (c) into a fine uniform powder; and
d) pyrolyzing said powder obtained from step (d) at a high temperature to yield the composite material for the anode electrode.

[0048] In an embodiment, the ratio of phenol and formaldehyde is the molar ratio of phenol and formaldehyde in the range of 1:1 to 1:5.

[0049] In an embodiment, the ratio of phenol and formaldehyde in the thermosetting phenolic resin solution is 1:2.5 by volume or 1:1 by molar ratio.

[0050] In an embodiment of the present invention, an electrochemical cell comprising:
a cathode electrode comprising a layered transition metal oxide;
an anode electrode comprising a phenolic resin based hard carbon - graphite composite comprising phenol and formaldehyde in a ratio ranging from 1:1 to 1:5 along with graphite whose percentage varies from 0.1 - 20 wt%. of phenol;
a separator; and
an electrolyte.

[0051] In an embodiment, the ratio of phenol and formaldehyde is the molar ratio of phenol and formaldehyde in the range of 1:1 to 1:5.

[0052] The anode made from the present phenolic-resin based hard carbon-graphite composite may be paired with any cathode to form an electrochemical cell/ battery. The aforesaid composite material, comprising the phenolic-resin based hard carbon-graphite material, may be deposited on the anode electrode by forming a layer of said composite material or an anode may be manufactured which may be made completely from the said composite material.

[0053] It is appreciated in the art that a separator may be any porous membrane that is placed between the electrodes and which are widely deployed in any standard lithium ion or electrochemical cells for preventing electric failures (like short circuit), facilitating ion movements, stopping the battery operation when the battery/ cell overheats, etc. Such separators may be placed between the electrodes of the electrochemical cell. Further, the separators may, for instance but not limited to, be any material made from polyolefin, ceramic oxides, natural minerals, etc.

[0054] In an embodiment, the electrolyte comprises of an alkali salt dissolved in an organic solvent with an additive. The alkali salt may be selected from Sodium hexafluorophosphate (NaPF6), Sodium perchlorate (NaClO4), Lithium hexafluorophosphate (LiPF6) or Potassium hexafluorophosphate (KPF6). Further, the organic solvent may be selected from Di-ethyl carbonate, Di-methyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene carbonate and the like. Further, the additive may be any inorganic and/or organic electrolyte additive like fluorinated ethylene carbonate (FEC) and the like which is widely known and appreciated in the art.Further, the electrolyte comprises of 0.8M NaPF6-PC: EMC: 2%FEC: 1%PST: 1% DTD.

[0055] In an embodiment, the present invention provides the synthesis of novel HC-Graphite composite via in situ particle anchoring method followed by carbonization at high temperatures.

[0056] In another embodiment, the present invention discloses the synthesis method of the composite called as a phenolic resin based hard carbon - graphite. The synthesis process involves mixing of thermosetting phenolic resin solution: phenol and formaldehyde solution in the molar ratio ranging from 1:1 to 1:5 under alkaline conditions along with graphite whose percentage varies from 0.1 - 20wt%.

[0057] The molar ratio between phenol and formaldehyde is 1:2.5 and preferably is 1:1.25.

[0058] In an embodiment, the ratio of phenol and formaldehyde in the thermosetting phenolic resin solution is 1:2.5 by volume or 1:1 by molar ratio.

[0059] The preferred graphite concentration is 10 wt% of the phenol and, more preferably, 5 wt%. The alkaline environment acts as a catalyst for the reaction. The final solution is charged into a reaction vessel to carry out hydrothermal reaction. The preferred temperature range for the hydrothermal reaction and curing is 100-180 deg. Celsius. Optionally, the preferred temperature range for the hydrothermal reaction and curing may also be 100-200 and 100-220 deg. Celsius.

[0060] The cured phenolic resin and graphite mixture are mechanically grounded into a powder. The said powder is kept in the tube furnace and inert gas is introduced. The preferred pyrolysis temperature is varied from 1000? to 1300? with a heating rate of 5-20?/min. In a more preferred embodiment, the heating rate is 5-15?/min and most preferably 5-10?/min. For the temperature range 1000-1300 ? the dwell time is varied from 1hr to 5 hrs. The carbonization under this condition ensures the structural regularity of the composite material.

[0061] In another embodiment, the charge-discharge profile of the present negative electrode active material exhibits a smooth discharging curve from 0V to 1.75V.

[0062] Typical electrolytes are Na, Li, K salts (as NaPF6, NaClO4, LiPF6, KPF6) dissolved in an organic solvent (e.g. di-ethyl carbonate, di-methyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene carbonate and the like).

[0063] A variety of electrolyte additives may be added to improve cycle stability, safety, high-temperature performance, etc. Typically, the electrolyte additive may be any inorganic and/or organic electrolyte additive like fluorinated ethylene carbonate (FEC) and the like which is widely known and appreciated in the art.

[0064] In an embodiment, the present invention discloses an electrode active material using phenolic resin based hard carbon - graphite composite in concurrence with a counter electrode and one or more electrolytes in energy storage devices.

[0065] In a preferred embodiment, the present invention discloses the alkali ion electrochemical cell comprising:
1) A Layered transition metal oxide-based cathode material;
2) A Phenolic resin based hard carbon-graphite composite as the anode material;
3) A separator between the positive and negative electrode material; and
4) An electrolyte consisting of an alkali salt dissolved in an organic solvent with electrolytic additives.

[0066] In an embodiment, the use of the said anode active material in secondary batteries like lithium-ion batteries, more particularly, Sodium-ion or potassium ion batteries that can deliver an excellent first discharge capacity and exhibit high initial columbic efficiency.

[0067] The following examples, which include the preferred embodiments, will serve to illustrate the practice of this invention. It is understood that the particulars shown are by way of example and for the purpose of illustrative discussion of preferred embodiments of the invention.

Examples:
[0068] The advantages of the present invention are discussed with regard to experimental examples:

Synthesis of hard carbon - graphite composite
[0069] Firstly, 20 gm of phenol and 25gm of formaldehyde were mixed and kept for stirring for approximately 30 mins to obtain a uniformly mixed clear solution. After that, 0.5ml of 10% NaOH solution was added to the mixture, which acts as a polymerizing catalyst for the reaction. The mixture was heated at 80? under stirring to remove water and to obtain a viscous liquid. 1gm of 5µm sized synthetic graphite (i.e.; 5% of Phenol content) was added to the solution. To achieve a uniform dispersion, the mixture was agitated for 30 minutes. The final mixture was then transferred into a Teflon-lined hydrothermal autoclave. The precursor mixture was hydrothermally treated in an oven at 180°C overnight and then cooled down naturally. Following the hydrothermal process, the solid polymerized phenolic resin block was rinsed with DI water and then dried. The solid block was then crushed to a coarse powder and then ball milled to obtain a fine uniform powder. The obtained powder was pyrolyzed, in a single step inside a tube furnace under N2 flow, following a particular temperature profile. The precursor was heated to 300°C initially, with a rate of 5°C/min. Once the desired temp is reached the temperature was increased to 450? and the ramp rate was set to 1?/min. The sample was heated at that temperature for one hour. The temperature was then raised to 900 degrees at a rate of 10 degrees per minute. Once the temperature reached 900 it was increased to 1300? at a rate of 5?/min. The material was kept at 1300°C for 2 hours before being cooled to 900°C at a rate of 5°C/min and subsequently to room temperature at a rate of 10°C/min. The received material has a tap density of 1.2-1.3gm/cc.

Half-cell performance of hard carbon - graphite composite
[0070] Hard carbon-graphite composite was mixed uniformly with carbon black in the desired ratio, preferably 91:5. The homogeneous powdered mixture was added to Na-CMC solution maintaining the ratio 91:5:4. The mixture was vacuum mixed for 1hr to form homogeneous slurry. The slurry was coated in the Aluminium current collector using the doctor blade technique. The coated electrodes were dried overnight in a vacuum oven to remove moisture. Half cells were made by using 0.8M NaPF6-PC: EMC: 2%FEC: 1%PST: 1% DTD as electrolyte.

[0071] Figure 1 shows the first charge-discharge profile of the anode material from the graph. The left curve (solid curve line falling from 1.5 V to 0.2 V) depicts the charging profile whereas the right curve (solid curve line rising from 0.2 V to 1.5 V) depicts the discharging profile of the anode material.

[0072] From Figure 1, the anode material shows a capacity of 296mAh/gm in the first discharge, with 60 % of the contribution coming from the plateau region and 40% coming from the sloppy region. From Figure 1, the plateau region is the horizontal region of the said profile below 0.2V whereas the sloppy region is the steep part of the said profile going from 0.2V to 1.5V. The majority of the portion for charge as well as discharge is below 0.2V, indicating better plateau capacity. As noted from Figure 2, the capacity for charging is close to 300mah/g (296mAh/gm) in the first cycle. The initial coulombic efficiency achieved is 86.6%.

[0073] The stability of the half-cell made from present anode composite material is assessed by analysing the trend of the discharge fading ratio and the cyclic performance (or capacity retention). The discharge fading ratio refers to the rate at which the half-cell’s discharge performance deteriorates over time or after several charge-discharge cycles whereas the capacity retention indicates how much of the original energy storage capacity is maintained over the time in the half-cell.

[0074] Figure 2 shows the stability of the half-cell made using hard carbon-graphite based anode material by plotting the discharge ratio. It is evident from the figure that the material is electrochemically stable. The discharge performance of the present half-cell is observed to be constant and capacity is retained (and not lost) across multiple cycles exceeding 50 cycles which is made clearer from Figure 3.

[0075] Figure 3 illustrates the cyclic performance (or capacity retention) of the half-cell having an anode made from the present phenolic based hard carbon - graphite composite material.

[0076] In an embodiment, the cyclic performance was evaluated at high charge and discharge rates for charging and discharging the complete half-cell in 15 minutes. The said performance is conducted by deploying the present anode in an industrially relevant 33140 format cylindrical cell which is well-known in the art for ion batteries. The typical 33140 cylindrical cells are 33 - 33.5 mm in diameter and 140 - 140.5 mm in height in size (as conveyed in the technical specification number 33140) and serves wide application in the field of renewable energy, energy storage devices, and telecom hardware units. As evident from Figure 3, the cell maintains high capacity retention of 82-85% even after 5000 cycles of being charged and discharged repeatedly at aggressive rates (~1000mA/g). When compared with the state-of-the-art ion-batteries, the present cell demonstrates high capacity retention of above 80% till 5000 cycles.

Advantages:
[0077] The present invention provides phenolic resin-based hard carbon-graphite composite as anode material for energy devices particularly in secondary batteries wherein little or no fading without significant loss in charge capacity while cycling is obtained.

[0078] The electrochemical properties of the anode product formed through the present synthesis method enhance battery performance with minimal capacity loss. The reduction in capacity fade is attributed to the stable structure and small graphitic domains that help stabilize the insertion and de-insertion of ions. Additionally, the cyclic stability of the battery is improved due to the controlled structure formed by the graphitic domains introduced during the resin formulation stage for making the anode composite material.

[0079] The present invention discloses a phenolic resin based hard carbon-graphite composite as an anode active material in secondary batteries or alkali-metal ion batteries which may improve the cyclic properties of secondary batteries. Though the present invention may apply to secondary batteries, it may also be appreciated that the present invention may also be applicable to electrical energy accumulators or more commonly occurring rechargeable batteries.

[0080] Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.
,CLAIMS:1. A phenolic resin based hard carbon-graphite composite as an anode material comprising a phenol and formaldehyde in a ratio ranging from 1:1 to 1:5 along with graphite, wherein the graphite percentage varies from 0.1 - 20 wt% of the phenol.

2. The phenolic resin based hard carbon-graphite composite as the anode material as claimed in claim 1, wherein the ratio of phenol and formaldehyde is 1:2.5 by volume or 1:1 by molar ratio.

3. The phenolic resin based hard carbon-graphite composite as the anode material as claimed in claim 1, wherein the preferred graphite concentration is 10 wt% of the phenol or 5 wt% of the phenol.

4. A method for synthesizing a composite material for an anode electrode, the method comprising steps of:
a) preparing a thermosetting phenolic resin solution by mixing phenol and formaldehyde under an alkaline solution in a molar ratio ranging from 1:1 to 1:5;
b) mixing graphite with the thermosetting phenolic resin solution in a predetermined quantity to obtain a precursor mixture;
c) performing a hydrothermal reaction on the precursor mixture obtained from step (a) to yield a polymerized phenolic resin;
d) crushing the polymerized phenolic resin obtained from step (c) into a fine uniform powder; and
d) pyrolyzing said powder obtained from step (d) at a high temperature to yield the composite material for the anode electrode.

5. The method as claimed in claim 4, wherein the predetermined quantity of graphite lies between 0.1% to 20% wt of the phenol.

6. The method as claimed in claim 4, wherein the alkaline solution in the process step (a) acts as a polymerizing catalyst.

7. The method as claimed in claim 4, wherein the hydrothermal reaction of step (c) is performed at the temperature of 100oC- 220oC.

8. The method as claimed in claim 4, wherein the pyrolysis of step (d) is carried out at the temperature from 1000? to 1300? with a heating rate of 5-20?/min.

9. An electrochemical cell comprising:
a cathode electrode comprising a layered transition metal oxide;
an anode electrode comprising a phenolic resin based hard carbon-graphite composite comprising phenol and formaldehyde in a molar ratio ranging from 1:1 to 1:5 along with graphite, wherein the graphite percentage varies from 0.1 - 20 wt% of the phenol;
a separator; and
an electrolyte.

10. The electrochemical cell as claimed in claim 10, wherein the electrolyte comprises of an alkali salt dissolved in an organic solvent with an additive.

11. The electrochemical cell as claimed in claim 11, wherein the alkali salt is selected from NaPF6, NaClO4, LiPF6 or KPF6.

12. The electrochemical cell as claimed in claim 10, wherein said anode is used with a counter electrode and with one or more electrolytes in an energy storage device.

13. The electrochemical cell as claimed in claim 10, wherein said anode is used in secondary batteries, electrical energy accumulators and/or rechargeable batteries.

14. The electrochemical cell as claimed in claim 14, wherein the secondary batteries may be lithium-ion batteries, sodium-ion and/or potassium ion batteries.

15. The electrochemical cell as claimed in claim 10, wherein the electrochemical cell achieves coulombic efficiency and discharge capacity of 86.6% and 296mAh/gm respectively and exhibits stability about 5000 cycles.