CLOSED LOOP PROCESS FOR NEAR ZERO-ENERGY REGENERATION OF ELECTRODES BY RECYCLING SPENT RECHARGEABLE LITHIUM BATTERIES

Abstract

The present invention relates to a rechargeable battery and a process near zero-energy regeneration of electrodes by recycling spent rechargeable batteries. The present invention relates to a process for near zero-energy regeneration of lithium iron phosphate (LiFePO.sub.4) or sodium iron phosphate (NaFePO.sub.4) cathode by recycling spent Lithium ferro phosphate rechargeable batteries.

Claims

1. A closed loop process for regeneration of LiFePO.sub.4 or NaFePO.sub.4 cathode from spent Lithium ferro phosphate rechargeable battery (LFP), the process comprising the steps of: a. de-lithiating the spent LFP electrode by microwave assisted chemical dilithiation, conventional hydrothermal assisted chemical dilithiation or chemical dilithiation with an oxidiser, wherein the ratio of LFP to oxidizer is 2:1 to form pure FePO4, dilithiation at a temperature range of 20° C.-150° C. for time ranging from 5 minutes-24 hours. b. chemically lithiating the FePO.sub.4 by adding a lithiating agent in a solvent based on the amount of FePO.sub.4—in stoichiometric ratio of FePO.sub.4 to lithiating agent at a temperature range of 25-100° C. for lithiation time ranging 1-30 minutes, or c. chemically sodiating the pure FePO.sub.4 by adding a sodiating agent in a solvent based on the amount of FePO.sub.4 in stoichiometric ratio of FePO.sub.4 to sodiating agent at a temperature of 25° C.-100° C. for sodiation time of ranging 1-30 minutes, d. obtaining the regenerated pure LiFePO.sub.4 or NaFePO.sub.4 electrodes with the characteristics as the original Lithium or sodium ferro phosphate battery (LFP).

2. The process as claimed in claim 1, wherein the oxidizer is one of potassium persulphate or sodium persulphate or a combination thereof.

3. The process as claimed in claim 1, wherein the stoichiometric ratio of Lithium ferro phosphate to the oxidizer is 2:1 in DI water.

4. The process as claimed in claim 1, wherein the dilithiation/oxidation is carried out using a micro-wave assisted chemical dilithiation or chemical dilithiation in oxidation solution.

5. The process as claimed in claim 4, wherein the dilithiation/oxidation is carried out for 15 mins in micro-wave at 250 W in deionized water.

6. The process as claimed in claim 4, wherein the chemical dilithiation/oxidation is carried out 24 hrs in oxidation solution.

7. The process as claimed in claim 1, wherein the solvent, for lithiation is one of, acetonitrile or isopropyl alcohol or a combination thereof.

8. The process as claimed in claim 1, wherein the lithiating agent is LiI or LiBr.

9. The process as claimed in claim 1, wherein the sodiating agent is NaI or NaBr.

10. The process as claimed in claim 1, wherein the ratio of ferro phosphate to the lithiating agent 1:3.5.

11. The process as claimed in claim 1, wherein the ratio of ferro phosphate to the sodiating agent 1:4.2.

12. The process as claimed in claim 1, wherein the process is a closed loop process.

13. A regenerated Lithium ferro phosphate electrode, wherein the regenerated electrode has a discharge capacity of 150 mAh/g at 1C; with 200 cycles at 5C; retaining 90% of initial capacity.

14. The regenerated sodium ferro phosphate electrode, wherein the regenerated electrode has a discharge capacity of 150 mAh/g at 1C; 150 cycles at a current rate of C/1.5 retaining 85%.

15. The process as claimed in claim 1, further comprises of LiMnPO.sub.4 or LiCoPO.sub.4 or mixed metal phosphates such as, LiFe.sub.xM.sub.1-xPO.sub.4 where M=Mn, Co, Ni and x may vary between 0 and 1.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0019] The accompanying drawings illustrate some of the embodiments of the present invention and together with the descriptions, serve to explain the invention. These drawings have been provided by way of illustration and not by way of limitation. The components in the drawings are not necessarily drawn to scale, emphasis instead being placed upon clearly illustrating the principles of the aspects of the embodiments.

[0020] FIG. 1.: Cycling performance of the commercial cell for 1000 cycles at 5 A current rate.

[0021] FIG. 2.: TGA analysis of the spent LFP electrode from 23° C. to 650° C. in air.

[0022] FIG. 3.: X-Ray diffraction pattern of (a) spent-LFP, (b) FP-MW, (c) CL-FP and (d) CS-FP. Standard LFP data from JCPDS file #01-081-1173 is also provided in the bottom panel.

[0023] FIG. 4.: Low magnification TEM images of and high-resolution TEM images of (a & e) spent LiFePO.sub.4, (b & F) chemically delithiated FePO.sub.4 (c & g) CL-FP and (d & h) CS-FP.

[0024] FIG. 5.: XPS spectra of spent Li.sub.xFePO.sub.4 and chemically delithiated FePO.sub.4 (a) survey spectrum (b) Fe 2p and (c) O 1s.

[0025] FIG. 6.: Electrochemical Performance of Microwave prepared FePO.sub.4 Upon Chemical Lithiation (a) 1.sup.st cycle charge-discharge profile at 1C rate (lithiated at 80° C.) (b) LIB rate performances of chemically lithiated FePO.sub.4 electrodes at different rates (lithiated at three different temperatures) and (c) cycling performance of CL-FP electrode at 5C for 300 cycles (lithiated at 80° C.)

[0026] FIG. 7.: Electrochemical Performance of Microwave prepared FePO.sub.4 Upon Chemical Sodiation (a) 1.sup.st cycle charge-discharge profile of chemically sodiated FePO.sub.4 sample at C/15 (Sodiated at 80° C.) (b) NIB rate performances of chemically sodiated FePO.sub.4 electrodes at different rates as indicated in legend (Sodiated at three different temperatures) and (c) cycling performance of the same electrode, initial 3 cycles at C/15 and then at C/1.5 (Sodiated at 80° C.).

[0027] FIG. 8.: Coulombic Efficiency plot of LiI-FP LIB cell at 5C rate.

[0028] FIG. 9.: Coulombic Efficiency plot of NaI-FP sodium ion cell, first 3 cycles at C/15 and following cycles at C/1.5.

[0029] FIG. 10.: Electrochemical rate performance of Chemically delithiated FePO.sub.4 (at 70° C.) and Chemical lithiated (at 80° C.).

DETAILED DESCRIPTION OF THE INVENTION

[0030] At the very outset of the detailed description, it may be understood that the ensuing description only illustrates a particular form of this invention. However, such a particular form is only exemplary embodiment, and without intending to imply any limitation on the scope of this invention. Accordingly, the description is to be understood as an exemplary embodiment and teaching of invention and not intended to be taken restrictively.

[0031] Unless defined otherwise, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Further, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular.

[0032] The present invention discloses a process which operates at a temperature ranging from 25° C. to 100° C. for recycling spent rechargeable batteries, a near zero-energy regeneration process of both lithium and sodium ion electrodes for use in rechargeable battery applications.

[0033] An aspect of the present invention is that the process can be modified depending on the type of the rechargeable battery for example, the spent Lithium ferro phosphate battery (LFP) which is first delithiated for the regeneration of ferro phosphate which is either converted to fresh Lithium ferro phosphate electrode (LFP) for Lithium-ion batteries, or sodium ion electrode for sodium ion batteries, for use in battery application.

[0034] In an embodiment the process includes dilithiation of the spent LFP batteries. The recycled ferro phosphate electrode, is subjected to lithiation process which operates at a temperature below or equal to 100° C. and hence is energy efficient for the recycle and regeneration of rechargeable batteries.

[0035] It is known in the art that a direct chemical lithiation process to supplement the deficient concentration of lithium in the recovered Lithium ferro phosphate battery (LFP) material for reuse is not suitable because the recovered LFP from different batteries will have varying degrees of Li deficiency and having a composition Li.sub.xFePO.sub.4 with x varying anywhere between 0 and 1. Further, conventional lithiation of spent Lithium ferro phosphate battery (LFP) promotes side reactions during chemical lithiation process that can lead to poor performance of the re-lithiated Lithium ferro phosphate battery (LFP).

[0036] In an embodiment, the process discloses recycling of spent lithium ferro phosphate battery wherein FePO.sub.4 is obtained by complete dilithiation (or oxidation of Li.sub.xFePO.sub.4). This homogenous FePO.sub.4 is subsequently lithiated chemically to form LiFePO.sub.4 without any high temperature processing. This LiFePO.sub.4 is then tested for its electrochemical performance as Li-ion battery cathode.

[0037] In another embodiment, the process discloses recycling of spent lithium ferro phosphate battery wherein FePO.sub.4 is obtained by complete dilithiation (or oxidation of Li.sub.xFePO.sub.4). This homogenous FePO.sub.4 is subjected to sodiation to form NaFePO.sub.4 without any high temperature processing such that the NaFePO.sub.4 can be reused as Na-ion battery cathode material.

[0038] Accordingly, an important embodiment of the present invention is for a process for regeneration of LiFePO.sub.4 or NaFePO.sub.4 cathode from spent Lithium ferro phosphate rechargeable battery (LFP), the process comprising the steps of: [0039] a. de-lithiating the spent LFP battery by adding an oxidizer in a molar ratio of 0.5 and the ratio of LFP to oxidizer is 2:1 to form pure FePO.sub.4, [0040] b. chemically lithiating the FePO.sub.4 by adding a lithiating agent in a solvent based on the amount of FePO.sub.4 in stoichiometric ratio of FePO.sub.4 to lithiating agent of 1:1.0-3.5 at a temperature of 25° C.-100° C. for lithiation time ranging 1-30 minutes, or [0041] c. chemically sodiating the pure FePO.sub.4 by adding a sodiating agent in a solvent based on the amount of FePO.sub.4 in stoichiometric ratio of FePO.sub.4 to sodiating agent of 1:1.0-4.2 at a temperature of 25° C.-100° C. for sodiation time of ranging 1-30 minutes, [0042] d. obtaining the regenerated pure LiFePO.sub.4 or NaFePO.sub.4 electrodes with the characteristics as the original lithium or sodium ferro phosphate battery (LFP or NFP).

[0043] In an aspect, the oxidizer is one of potassium persulphate (K.sub.2S.sub.2O.sub.8) or sodium persulphate (Na.sub.2S.sub.2O.sub.8) a combination thereof.

[0044] In another aspect, the dilithiation/oxidation is carried out using a micro-wave assisted chemical process in oxidation solution or chemical process in oxidation solution.

[0045] The dilithiation/oxidation is carried out for 15 mins in micro-wave (with 250 W power) in oxidation solution and mole ratio of LFP to oxidizer is 2:1 (example: 1 gram of spent LFP, 0.86 gram of K.sub.2S.sub.2O.sub.8 oxidizer in 30 ml of DI water).

[0046] The chemical dilithiation/oxidation is carried for 1 hr. in an oxidation solution in the mole ratio of 2:1 (example: 1 gram of LFP, 0.86 gram of K.sub.2S.sub.2O.sub.8 oxidizer in 30 ml of DI water) on a hot plate at a temperature of 70° C.

[0047] The solvent for dilithiation is deionized water.

[0048] The solvent for lithiation is one of, acetonitrile or isopropyl alcohol.

[0049] In an aspect the process of lithiation is carried at a temp ranging 25° C. to 100° C.

[0050] In an aspect the process of lithiation time ranges from 1-30 minutes.

[0051] In an aspect the lithiating agent of the process is one of lithium iodide (LiI) or lithium bromide (LiBr).

[0052] In another aspect the sodiating agent of the process is one of sodium iodide (NaI) or sodium bromide (NaBr).

[0053] In an embodiment the disclosure is for a regenerated lithium ferro phosphate electrode or a sodium ferro phosphate electrode obtained by recycling the spent LFP rechargeable batteries from the process of the invention.

[0054] The regenerated lithium ferro phosphate electrode delivered discharge capacity of 150 mAh/g at 1C and was able to cycle for 200 cycles at 5C rate retaining 90% of initial capacity.

[0055] The regenerated sodium ferro phosphate electrode delivered discharge capacity of 150 mAh/g at 1C and was able to provide 85% capacity retention for 150 cycles at a current rate of C/1.5.

[0056] The closed loop process for recycling spent LFP batteries is done with compounds similar to LiFePO.sub.4 compound, such as: LiMnPO.sub.4 or LiCoPO.sub.4 and even mixed metal phosphates such as, LiFe.sub.xM.sub.1-xPO.sub.4 (where M=Mn, Co, Ni and x may vary between 0 and 1).

Abbreviations and Definitions

[0057] Spent-LFP—spent Lithium phosphate electrode recovered from a failed battery, FP-MW microwave delithiated Spent-LiFePO.sub.4,

[0058] CL-FP chemically lithiated FePO.sub.4 and CS-FP for chemically sodiated FePO.sub.4 respectively.

[0059] Closed loop process—is defined as a process including recovery from the spent battery, oxidizing to FePO.sub.4 and chemically lithiating or sodiating to produce regenerated LFP or NaFP

[0060] Stoichometric ratio—the mole fraction of LFP to oxidizer.

[0061] Spent/failed batteries are used synonymously and have the same meaning and used interchangeably throughout the specification.

EXAMPLES

[0062] Without limiting the scope of the present invention as described above in any way, the present invention has been further explained through the examples provided below.

[0063] Obtaining Spent Lithium Ferro Phosphate Electrode from Spent Lithium Ferro Phosphate Batteries

[0064] Lithium ferro phosphate electrode was obtained from spent LFP rechargeable batteries. The failed battery cathode (LiFePO.sub.4) was removed from the aluminum current collector by an ultra-sonication process.

[0065] Extraction of spent LFP cathode was carried out from a commercially obtained 5 Ah cylindrical cell that was cycled at a current of 5 A for 1000 cycles in the voltage window from 2.5 to 4 V in the lab. Though the cell performed well in the initial cycles, capacity retention of merely 36% was observed at the end of 1000 cycles which is considered as failed cell (FIG. 1). The loss of Li in the sample is confirmed by the presence of FePO.sub.4 denoted by asterisk in the spectra of FIG. 1a with the overall structure corresponding to that of LFP Olivine.

[0066] Dilithiation of Spent LFP Electrode to Prepare FePO.sub.4:

[0067] Microwave Assisted Chemical Dilithiation:

[0068] For recycling the spent LFP electrode to prepare FePO.sub.4, a microwave assisted chemical dilithiation to obtain spent FePO.sub.4 powders (FP-MW) was carried out. The same FePO.sub.4 powders (FP-MW) was used for both lithium and for sodium ion battery applications. The choice of microwave assisted process is in its potential to be used in lab scale as well as extendable to large scale and the process results in rapid material preparation. A stoichiometric mixture of spent LFP and K.sub.2S.sub.2O.sub.8 (LFP:K.sub.2S.sub.2O.sub.8 is 2:1 mole ratio, example: for 1 gram of spent LFP, 0.9 gram in 30 ml of DI water) was treated in a microwave at a power of 250 W for 15 minutes. Resulting solution was washed to neutralize the pH and dried to obtain delithiated LFP or FePO.sub.4.

[0069] Conventional Hydrothermal Assisted Chemical Dilithiation:

[0070] For recycling the spent LFP electrode to prepare FePO.sub.4, a conventional hydrothermal assisted chemical dilithiation to obtain spent FePO.sub.4 powders (FP-MW) was carried out. The same FePO.sub.4 powders (FP-MW) could be used for both lithium and for sodium ion battery applications. The choice of conventional hydrothermal assisted process is in its potential to be used in lab scale as well as extendable to large scale and the process results in rapid material preparation. A stoichiometric mixture of spent LFP and K.sub.2S.sub.2O.sub.8 (LFP:K.sub.2S.sub.2O.sub.8 is 2:1 mole ratio, example: for 1 gram of spent LFP, 0.9 gram in 30 ml of DI water) was treated in a conventional hydrothermal system at a temperature of 100° C. for 60 minutes. Resulting solution was washed to neutralize the pH and dried to obtain delithiated LFP or FePO.sub.4.

[0071] Chemical Dilithiation:

[0072] For recycling the spent LFP electrode to prepare FePO.sub.4, chemical dilithiation to obtain spent FePO.sub.4 powders (FP-MW) was carried out. The same FePO.sub.4 powders (FP-MW) was used for both lithium and for sodium ion battery applications. A stoichiometric mixture of spent LFP and K.sub.2S.sub.2O.sub.8 was treated on a hot plate at 70° C. for 1 hour and the resulting solution was washed to neutralize the pH and dried to obtain delithiated LFP or FePO.sub.4.

[0073] The possible chemical dilithiation reaction may be given as

LiFePO.sub.4+0.5K.sub.2S.sub.2O.sub.8.fwdarw.FePO.sub.4+0.5Li.sub.2SO.sub.4+0.5K.sub.2SO.sub.4  Equation-1

LiFePO.sub.4+0.5Na.sub.2S.sub.2O.sub.8.fwdarw.FePO.sub.4+0.5Li.sub.2SO.sub.4+0.5Na.sub.2SO.sub.4  Equation-2

[0074] The high redox activity of K.sub.2S.sub.2O.sub.8/K.sub.2SO.sub.4 couple resulted in the dilithiation/oxidation of spent-LFP to form FePO.sub.4.

[0075] Regeneration of Li.sub.xFePO.sub.4 Spent Li-Ion Battery:

[0076] The homogenous FePO.sub.4 obtained by dilithiation process either chemically or microwave assisted is subsequently lithiated chemically to form LiFePO.sub.4 in LiI solution with stoichiometric concentration of LiI 240 mg of FePO.sub.4 mixed with a solution containing 320 mg of LiI in 10 ml of acetonitrile (excess LiI is required for complete lithiation of FePO.sub.4) at a temperature of 100° C. for 15 min without any subsequent high temperature annealing process.

[0077] The possible chemical lithiation reaction may be given as

FePO.sub.4+3/2LiI.fwdarw.LiFePO.sub.4+½LiI.sub.3  Equation-3

FePO.sub.4+3/2LiBr.fwdarw.LiFePO.sub.4+½LiBr.sub.3  Equation-4

[0078] The homogenous FePO.sub.4 obtained by dilithiation process either chemically or microwave assisted is subsequently lithiated chemically to form LiFePO.sub.4 in LiI solution with stoichiometric concentration of LiI. 240 mg of FePO.sub.4 mixed with a solution containing 320 mg of LiI in 10 ml of acetonitrile (excess LiI is required for complete lithiation of FePO.sub.4) at a temperature of 80° C. for 15 min without any subsequent high temperature annealing process.

[0079] Regeneration of Na.sub.xFePO.sub.4 from Spent Li-Ion Battery:

[0080] The homogenous FePO.sub.4 obtained by dilithiation process either chemically or microwave assisted is subsequently sodiated chemically to form NaFePO.sub.4 in NaI solution with stoichiometric concentration of Nat 240 mg of FePO.sub.4 mixed with a solution containing 320 mg of NaI in 10 ml of acetonitrile (excess LiI is required for complete lithiation of FePO.sub.4) at a temperature of 100° C. for 15 min without any subsequent high temperature annealing process

[0081] The possible chemical sodiation reaction may be given as

2FePO.sub.4+3/2NaI.fwdarw.NaFePO.sub.4+½NaI.sub.3  Equation-5

2FePO.sub.4+3/2NaBr.fwdarw.NaFePO.sub.4+½NaBr.sub.3  Equation-6

[0082] The homogenous FePO.sub.4 obtained by dilithiation process either chemically or microwave assisted is subsequently sodiated chemically to form NaFePO.sub.4 in NaI solution with stoichiometric concentration of Nat 240 mg of FePO.sub.4 mixed with a solution containing 320 mg of NaI in 10 ml of acetonitrile (excess LiI is required for complete lithiation of FePO.sub.4) at a temperature of 80° C. for 15 min without any subsequent high temperature annealing process

[0083] Structural, Morphological, and Surface Chemical Characterization of the Recovered Li.sub.xFePO.sub.4, Recycled FePO.sub.4 and Regenerated CS-FP (LiFePO.sub.4) and CL-FP (NaFePO.sub.4):

[0084] The success of chemical dilithiation to obtain FePO.sub.4 in the microwaved sample (FP-MW) was also investigated via XRD (FIG. 3b). The 15-minute microwave process was reasonably enough to completely delithiate the sample as can be seen from the XRD pattern. The resulting FePO.sub.4 retained the orthorhombic crystal structure which was utilized for sodium ion battery applications. Extend of chemical lithiation and sodiation by using LiI/NaI was confirmed by XRD technique. FIG. 3c represents the LiI lithiated LFP (CL-FP) while FIG. 3d represents the NaI sodiated NFP (CS-FP). Both CL-FP and CS-FP holds olivine structure (LiFePO.sub.4 and NaFePO.sub.4) with Pnma space group. Thus, from the spectra it can be confirmed that effective lithiation/sodiation can be done by utilizing LiI/NaI as reducing agents.

[0085] FIG. 4a, b, c, d represents the low magnification TEM images and FIG. 4e, f, g, h represents the high-resolution TEM images of spent-LFP, MW processed FP, CL-FP and CS-FP respectively. TEM image provided as FIG. 4a shows that spent LiFePO.sub.4 particles are irregular shaped with an average size range of nearly 200 nm. Chemically delithiated FePO.sub.4 sample also held similar particle morphology as evident from the low magnification images (refer FIG. 4b). Thus, it can be confirmed that the microwave treatment could not invoke any morphological change rather it removes the Li present in the spent electrode without destructing the particle morphology. Similar particle size was observed for CL-FP (FIG. 4c) and CS-FP (FIG. 4d). This implies that chemical treatment with LiI/NaI does not invoke any morphological change as it was a low temperature process.

[0086] HRTEM images (FIG. 4e, f, g, h) further confirms the crystalline nature of all the samples. Spent LiFePO.sub.4 hold a d-spacing consistent with the LiFePO.sub.4 (0.51 nm corresponding to (200)) while microwave processed FePO.sub.4 has a d-spacing of 0.48 nm corresponding to (200) planes. CL-FP sample was observed to have a d-spacing of 0.51 nm confirming proper lithiation while CS-FP sample holds a d-value of 0.45 nm consistent with the (101) plane of NaFePO.sub.4.

[0087] Surface chemical analyses of the samples as seen in FIG. 5 were conducted using X-ray photo electron spectroscopy. FIG. 5a shows the XPS survey spectrum which provides information about the elements present in all four samples. All samples have similar elemental composition (Fe, P, O, C, F etc.) expect that CS-FP shows the presence of sodium (Na KLL) in the sample. Presence of fluorine in the sample can be related to the PVDF additive being used during electrode fabrication. High resolution Fe 2p can be utilized to confirm the oxidation change of Fe in the samples. As can be seen from the high-resolution Fe 2p spectra (FIG. 5b), spent-LFP sample holds mixed oxidation states of both Fe.sup.2+ and Fe.sup.3+. This could be due to the loss of Li in the cycled sample resulting in the occurrence of both LFP and FP in the sample and is consistent with the XRD spectrum provided before. However, FePO.sub.4 was observed to have predominantly Fe.sup.3+ which further confirms the complete dilithiation of spent electrode under microwave processing. Both CL-FP and CS-FP shows Fe 2p.sub.3/2 spectra peaks at around 711 eV confirming the prevalence of Fe in 2+ oxidation state. However, the slight shifts in peaks could be ascribed to the delocalized surface distortions emerging due to the chemical treatment processes. O 1s (FIG. 5c) indicates peaks at ˜531 eV, corresponding to the lattice oxygen and is consistent for all the samples. Nevertheless, an additional peak was observed around 533 eV in the CL-FP sample which correlates to the surface carbon contamination (emerging due to carbon additive).

[0088] Electrochemical Characterizations:

[0089] Failure of a commercial lithium-ion cell could predominantly be because of three reasons. i) failure of battery components (anode/cathode/current collector), ii) electrolyte boil off/leakage and iii) battery abuse (overcharging, dendritic growth, gas evolution etc.). Herein, cycled commercial cell retained only 36% of its initial capacity at the end of 1000 cycles. This can be considered as a completely drained cell. This spent LFP electrode was reused for lithium-ion battery applications. In order to do so, the spent LFP material recovered from the failed commercial cell (without any processing upon recovery) was slurry casted. TGA analysis was done on the spent electrode to confirm the weight percentage of LFP in the commercial cell and was estimated to be nearly 90% (FIG. 2). Depending on the concentration of LiI, complete lithiation is possible and this transformation is visible from the XRD spectrum provided as FIG. 3c. This chemically lithiated LiFePO.sub.4 (CL-FP) was tested for its electrochemical performances as a lithium-ion battery cathode. The half-cell was initially tested at a rate of 1C (FIG. 6a) wherein the cell delivered a discharge capacity of 145 mAh/g (all the capacities values are based on the active weight of LFP) which further confirm the potential of this chemical lithiation process. FIG. 6b indicates the rate capability of the half-cell wherein the cell delivered discharge capacity of 107 mAh/g even at a high rate of 10C. Another feature is the capability of the cell to deliver capacity of 148 mAh/g even after ramping from 10C to 1C, which denotes its excellent reversibility. FIG. 6c shows the cycling performance of the regenerated LFP for 300 cycles at a rate of 5C. The electrode demonstrated a flat discharge capacity profile with a value of 110.5 mAh/g and a retention value of 95% at the end of 300 cycles. Moreover, the Coulombic efficiency value reached 99% in the 3.sup.rd cycle and stable thereafter demonstrating excellent reversibility (refer FIG. 8). Thus, based on the above results chemical lithiation taught by the present invention can be considered as a feasible approaching in recycling and regeneration of spent LFP based batteries.

[0090] The obtained sample was structurally characterized using XRD analysis and confirmed the crystal structure as NaFePO.sub.4 (refer FIG. 3d).

[0091] FIG. 7 display the electrochemical performance of the chemically sodiated FePO.sub.4 electrode. At a current density of C/15, the electrode delivered charge capacity of 125 mAh/g while the discharge capacity improved to 138 mAh/g. FIG. 7b shows the rate performance of the electrodes at rates ranging from C/6 to C/1.5, as indicated in the figure. Even after ramping from C/6 to C/1.5, the chemically sodiated electrode maintained 79% of the capacity which was delivered at C/6. Moreover, reverting the cell back to C/6 from C/1.5, the delivered capacity was almost 96% of the value provided at the 5.sup.th cycle. Cycling study was also tested similar to electrochemically sodiated cell, initial 3 cycles at C/15 and then at C/1.5. Capacity delivered at the initial 3 cycles was 138 mAh/g and was further able to retain 77% of the initial capacity displayed at C/1.5 for 100 cycles. Though the initial Coulombic efficiency was beyond 100% (since additional sodium is supplemented from the metallic electrode), the cell delivered an average Coulombic efficiency of 99.5% in the subsequent cycles (FIG. 9). From the electrochemical results it can be confirmed that a commercially viable chemical sodiation process can also be adopted in recycling such spent LFP batteries. From the data provided in Table 1 and Table 2, it can be seen that the present set of data is comparable to freshly prepared NaFePO.sub.4 sodium ion battery reports and freshly prepared LiFePO.sub.4 lithium ion battery reports available in literature. The chemically delithiated (on a hot plate at 70° C.) was tested for its electrochemical rate performance and the results are displayed in FIG. 10.

TABLE-US-00001 TABLE 1 Electrochemical performance comparison of NaFePO.sub.4 cathodes available in literature Sl. NaFePO.sub.4 Capacity No. Sample Details C-Rate or (Current) (mAh/g) Reference 1 NaFePO.sub.4-MWCNT C/10 (15.4 mA/g) 90 24 2 Triphylate NaFePO.sub.4 C/10 (15.4 mA/g) 132 25 1C (154 mA/g) 95 5C (770 mA/g) 66 20C (3080 mA/g) 25 3 NaFePO.sub.4 C/20 (7.5 mA/g) 120 26 1C (154 mA/g) 60 4 Olivine C/10 (15.4 mA/g) 111 27 NaFePO.sub.4− microsphere 1C (154 mA/g) 71 2C (308 mA/g) 46 5 Polythiophene coated C/15.4 (10 mA/g) 141.5 28 NaFePO.sub.4 Uncoated NaFePO.sub.4 108 6 NaFePO.sub.4/Graphene C/10 (15.5 mA/g) 142 29 1C (154 mA/g) 79 3C (462 mA/g) 67 5C (770 mA/g) 51 7 NaFePO.sub.4 C/20 (7.5 mA/g) 125 30 8 Maricite NaFePO.sub.4 C/20 (7.5 mA/g) 142 31 9 FP-MW C/15 (11.11 mA/g) 159 This work (1C assumed as C/6 (27.75 mA/g) 139 167 mAh/g) C/3 (83.25 mA/g) 114 C/1.5 (111 mA/g) 100 10 CS-FP C/15 (11.11 mA/g) 138 This work (1C assumed as C/6 (27.75 mA/g) 120 167 mAh/g) C/3 (83.25 mA/g) 107 C/1.5 (111 mA/g) 95

TABLE-US-00002 TABLE 2 Electrochemical performance comparison of fresh LiFePO.sub.4 cathodes available in literature with reused and recycled LFP cells (1C = 167 mA/g) Sl Capacity No. LiFePO.sub.4 Sample details C-Rate (mAh/g) Reference 1 LFP C/5  110 32  1C 80 LFP + 1% Cu C/5  140  1C 100 2 C-LFP C/10 145 33 10C 50 C-LFP/7% Polypyrrole C/10 148 10C 100 3 LFP Bare C/10 146 34  5C 90 LFP Surfactant C/10 170  5C 142 4 LFP C/10 132 35  5C 83.4 5 LFP C/10 118 36 F-Doped LFP C/10 175 6 LFP C/10 140 37 10C 70 LFP/Nanofibers C/10 150 10C 80 7 LFP @ Glucose C/5  160 38 10C 100 8 Commercial LFP  1C 130 39 30C 60 Self-assembled LFP  1C 150 30C 110 9 Recycled LFP  1C 150 This work 10C 95 10 CL-FP  1C 145 This work 10C 107

Advantages

[0092] Thus, the present invention demonstrates a facile way and means to reuse/recycle/regenerate spent LFP for lithium as well as sodium ion battery applications. It is well established that the spent Lithium ferro phosphate battery (LFP) electrode can be reused for lithium-ion battery without much complicated processing or high temperature treatment.

REFERENCES

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