Boron-Containing Plastic Crystal Polymer and Preparation Method therefor and Application thereof

Abstract

The present invention discloses a boron-containing plastic crystal polymer and a preparation method therefor and an application thereof. The described preparation method comprises the following step: curing a mixture containing a plastic crystal, a metal salt, a monomer and a photoinitiator. The plastic crystal polymer prepared by the present invention can be used as all-solid electrolyte, without any liquid additive being added therein. The obtained electrolyte has a room-temperature ionic conductivity up to 3.6×10−4 S/cm, and shows a high sodium ion transference number and a wide electrochemical window up to 4.7V. The present invention further prepares composite positive and negative electrodes for positive and negative electrode modification of a sodium ion battery. A finally assembled all-solid sodium ion battery shows good rate performance and cycle stability at room temperature, achieving a specific discharge capacity up to 104.8 mAh/g at room temperature and a capacity retention ratio of 85.4% after 80 cycles.

Claims

1. A method for preparing a boron-containing plastic crystal polymer, comprising the following steps: curing a mixture containing a plastic crystal, a metal salt, a monomer and a photoinitiator; the monomer is a boron-containing ternary crosslinker, the structure of which is shown below: ##STR00002## wherein, the value of n is 1 to 20; the plastic crystal is succinonitrile.

2. The method according to claim 1, wherein, the plastic crystal is mixed with the metal salt to obtain a mixed solution and then mixed with the monomer and the photoinitiator to obtain the mixture.

3. The method according to claim 2, wherein, the method for preparing the mixture comprises the following steps: (1) mixing the metal salt with the plastic crystal, heating and stirring to obtain a mixed solution; (2) mixing the mixed solution obtained in step (1) with the boron-containing ternary crosslinker and the photoinitiator to obtain the mixture.

4. The method according to claim 1, wherein, the metal salt is sodium salt, lithium salt or aluminum salt; or the photoinitiator is 2-hydroxy-2-methyl-1-phenylacetone or 1-hydroxycyclohexyl phenyl ketone; or, the curing is ultraviolet curing; or, the mixture is added to a porous support material before the curing; or, the mixture is present in liquid form; or, the mixture is formed from the plastic crystal, the metal salt, the monomer and the photo initiator.

5. The method according to claim 4, wherein, when the mixture is added to the porous support material, a porous support material containing the mixture is sandwiched between two glass sheets before subsequent curing.

6. A boron-containing plastic crystal polymer prepared by the method as defined in claim 1.

7. A use of the boron-containing plastic crystal polymer as defined in claim 6 as solid-state electrolyte in an all-solid-state ion battery.

8. An all-solid-state ion battery containing the boron-containing plastic crystal polymer as defined in claim 6.

9. A method for preparing an all-solid-state ion battery, comprising the following steps: (1) immersing an electrode sheet in the mixture as defined in claim 1 until the mixed solution is fully immersed into the inside of the electrode sheet, curing to obtain a composite positive and negative electrode sheet prepared in situ; (2) sandwiching the boron-containing plastic crystal polymer as defined in claim 6 between the composite positive and the negative electrode sheet, and assembling.

10. The method according to claim 9, wherein, the electrode sheet may be prepared by the following steps: (1) adding a positive/negative electrode active material for ion batteries, a conductive agent and a binder to N-methylpyrrolidone solvent and homogenizing to obtain a slurry; (2) evenly coating the slurry on aluminum foil, and drying in vacuum.

11. The method according to claim 2, wherein, a concentration of the metal salt in the mixed solution is 0.25 to 1.25 mol/L.

12. The method according to claim 11, wherein, the concentration of the metal salt in the mixed solution is 1 mol/L.

13. The method according to claim 1, wherein, in the mixture, a concentration of the boron-containing ternary crosslinker is 8 to 30 wt. %; or, an amount of the photoinitiator is 0.5 to 5 wt. % of the boron-containing ternary crosslinker; or, the value of n is 1, 6 or 20.

14. The method according to claim 13, wherein, in the mixture, the concentration of the boron-containing ternary crosslinker is 10 wt. %; or, the amount of the photoinitiator is 1 wt. % of the boron-containing ternary crosslinker.

15. The method according to claim 4, wherein, the sodium salt is one or more of sodium perchlorate, sodium hexafluorophosphate, sodium bis(oxalate)borate and sodium trifluoromethanesulfonate; or, the addition is injection; or, the porous support material is one or a composite film of polyacrylonitrile nonwoven fabric, polypropylene hydrocarbon nonwoven fabric, cellulose film, glass fiber, polyethylene terephthalate film and polyimide nonwoven film.

16. The method according to claim 15, wherein, the porous support material is polyacrylonitrile nonwoven fabric, polypropylene-cellulose composite nonwoven fabric or cellulose film.

17. The method according to claim 10, wherein, in step (1), a mass ratio of the positive/negative electrode active material for the ion batteries to the conductive agent is (3 to 16): 1, a mass ratio of the binder to the conductive agent is (0.25 to 4): 1, and the homogenization time is 2 to 4 hours; or, the positive electrode active material is layered oxide, sodium vanadium phosphate, sodium iron sulfate, sodium ion fluorophosphate, Prussian blue, Prussian white, sodium vanadium fluorophosphate, sodium iron fluorophosphate, sodium manganese oxide or sodium cobalt oxide; or, the negative electrode active material is sodium metal, hard carbon or molybdenum disulfide; or, the conductive agent is Super P, acetylene black or Ketjen black; or, the binder is one or more of PVDF, sodium carboxymethyl cellulose and sodium alginate.

18. The method according to claim 17, wherein, in step (1), the mass ratio of the positive/negative electrode active material for the ion batteries to the conductive agent is 8:1, and the mass ratio of the binder to the conductive agent is 1:1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG. 1 shows the cycle stability of the all-solid-state battery at room temperature assembled with boron-containing and boron-free plastic crystal electrolytes as described in embodiment 1 and comparative embodiment 1, respectively.

[0038] FIG. 2 shows the discharge curves of the all-solid-state sodium ion battery described in embodiment 1 at different current densities.

[0039] FIG. 3 shows the discharge curves of the all-solid-state sodium ion battery described in comparative embodiment 1 at different current densities.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Embodiment 1

[0040] 1. Preparation of a Boron-Containing Ternary Crosslinker (B-Crosslinker)

[0041] 2.6 mL of trimethyl borate and 8.5 mL of hydroxyethyl methacrylate were measured and dissolved in 25 mL of anhydrous acetonitrile, and the mixed solution was stirred and reacted for 3 to 4 hours at 50° C. under the protection of inert atmosphere. Then, the temperature was raised to 70° C., and the stirring was continued for 3 to 5 hours to remove the methanol produced in the reaction to ensure the complete reaction. After the reaction was completed, the unreacted trimethyl borate and residual solvent were removed by distillation under reduced pressure, and dried under vacuum for 48 hours. The obtained light yellow liquid product (i.e., B-crosslinker) was sealed and stored in a glove box for future use to prevent hydrolysis (for the specific preparation method, see literature: ACS Appl. Mater. Interfaces 2016, 8, 27740-27752).

[0042] The boron-containing ternary crosslinker (B-crosslinker) used in the following embodiments and comparative embodiments were prepared according to this preparation method.

[0043] 2. Preparation of an all-Solid-State Plastic Crystal Polymer Electrolyte Film

[0044] A certain amount of sodium perchlorate (NaClO.sub.4) was weighed and added to succinonitrile (SN), and the mixture was heated and stirred to form a transparent and uniform NaClO.sub.4 salt solution 1 of succinonitrile, in which a concentration of NaClO.sub.4 in SN was 1 mol/L. Then a certain amount of the B-crosslinker (n=1) was added to the solution 1, and a certain mass fraction of 1173 photoinitiator was added to the system at the same time, and the stirring was continued to make a homogeneous solution 2. In the solution 2, a mass fraction of the added B-crosslinker (n=1) was 12 wt. %, and a content of the photoinitiator 1173 was 1 wt. % of the mass of the active monomer B-crosslinker (n=1). Then, the mixed solution was injected to the polypropylene-cellulose composite nonwoven fabric, and after the solution was completely immersed. The nonwoven fabric containing the mixed solution was sandwiched between two clean glass sheets, and was cured into a film by ultraviolet curing technology, so that the final all-solid-state plastic crystal polymer electrolyte was obtained.

[0045] The ionic conductivity of the all-solid-state plastic crystal polymer electrolyte was tested:

[0046] The electrolyte film was sandwiched between two stainless steel sheets and placed in a 2032 battery case, and then the ionic conductivity of the electrolyte was measured by electrochemical AC impedance spectroscopy, and the ionic conductivity was calculated by the formula: σ=d/SR.sub.b, where, d is the thickness of the electrolyte, S is the area of the stainless steel sheet at room temperature, and R.sub.b is the measured bulk impedance. The all-solid-state polymer electrolyte was tested to have an ionic conductivity of 3.6×10.sup.−4 S/cm at 25° C.

[0047] The electrochemical window of the all-solid-state plastic crystal polymer electrolyte was tested: the stainless steel sheet and a sodium sheet were used as working electrode and reference electrode respectively, and the electrolyte was sandwiched between them and placed in 2032 battery case. The electrochemical window of the electrolyte was measured by linear sweep voltammetry using an electrochemical workstation, the test temperature was 25° C., the starting potential was 2.0V, the highest potential was 6.0V, and the scanning speed was 0.5 mV/s. The electrochemical window of the all-solid-state plastic crystal polymer electrolyte was tested to be 4.7 V. The sodium ion migration number of the all-solid-state plastic crystal polymer electrolyte was tested: The electrolyte film was sandwiched between two sodium sheets, and the sodium ion migration number was measured by electrochemical AC impedance combined with DC polarization. The sodium ion migration number of the electrolyte was calculated by the formula

[00001]$t_{{\mathrm{Na}}^{+}}=\frac{I_s{R}_f\left(\Delta V-I_0{R}_I^0\right)}{I_0{R}_i\left(\Delta V-J_s{R}_I^s\right)}.$

Among them, ΔV is the DC voltage applied to both sides of the electrode, I.sub.0 and I.sub.s are the initial and stabilized current values respectively, R.sub.i and R.sub.f are the initial and polarized impedances of the electrolyte film, R.sub.I.sup.0 and R.sub.I.sup.s are the initial and polarized interface impedances of the electrode e/electrolyte respectively. The solid-state polymer electrolyte was tested to have a sodium ion migration number of 0.62 at 25° C.3. In-situ preparation of a sodium ion battery composite electrode

[0048] Preparation of a composite positive/negative electrode: polyvinylidene fluoride (PVdF) was dissolved in N,N-2-methylpyrrolidone at a concentration of 0.1 mol/L. Then the positive electrode active material layered oxide Na.sub.1/3Fe.sub.1/3Mn.sub.1/3O.sub.2/ negative electrode active material hard carbon, binder PVdF, and conductive agent Super P were mixed in a mass ratio of 8:1:1 and ground for at least 1 hour. The slurry obtained from the previous steps was evenly coated on the aluminum foil, vacuum dried and then cut according to the size. Next, the cut electrode sheet was immersed in the above mixture solution 2 to allow the reaction precursor solution to enter the inside of the electrode, and finally the electrode sheet was taken out and placed under an ultraviolet lamp for ultraviolet curing to obtain the final composite positive/negative electrode.

[0049] The composite Na.sub.1/3Fe.sub.1/3Mn.sub.1/3O.sub.2 electrode prepared above was used as the positive electrode and the composite hard carbon was used as the negative electrode, the plastic crystal polymer electrolyte was assembled into the all-solid-state sodium battery, and this embodiment was measured with a LAND battery charging and discharging instrument, as shown in FIG. 2 and FIG. 3. The discharge specific capacity of the all-solid-state sodium battery assembled with this plastic crystal polymer electrolyte was tested to be 104.8 mAh/g at room temperature, and after 80 cycles, the capacity retention rate was 85.4% (FIG. 1); and the all-solid-state sodium ion battery assembled with this solid-state polymer electrolyte had good rate performance, with a discharge capacity of 80.24 mAh/g at current density of 0.5 A/g.

Embodiment 2

[0050] 1. Preparation of an all-Solid-State Plastic Crystal Polymer Electrolyte Film

[0051] A certain amount of sodium trifluoromethanesulfonate (NaOTf) was weighed and added to succinonitrile (SN), and the mixture was heated and stirred to form a transparent and uniform NaOTf salt solution 1 of succinonitrile, in which the concentration of NaOTf in SN was 1.25 mol/L. Then a certain amount of the B-crosslinker (n=6) was added to the solution 1, and a certain mass fraction of 184 photoinitiator was added to the system at the same time, and stirring was continued to make a homogeneous solution 2. In the solution 2, the mass fraction of B-crosslinker (n=6) was 30 wt. %, and the content of photoinitiator 184 was 5 wt. % of the mass of active monomer B-crosslinker (n=6). Then, the mixed solution was injected to the polyacrylonitrile nonwoven fabric, and after the solution was completely immersed. The nonwoven fabric containing the mixed solution was sandwiched between two clean glass sheets, and was cured into a film by ultraviolet curing technology, so that the final all-solid-state plastic crystal polymer electrolyte was obtained.

[0052] The ionic conductivity of the all-solid-state plastic crystal polymer electrolyte was tested:

[0053] The electrolyte film was sandwiched between two stainless steel sheets and placed in a 2032 battery case, and then the ionic conductivity of the electrolyte was measured by electrochemical AC impedance spectroscopy, and the ionic conductivity was calculated by the formula: σ=d/SR.sub.b, where, d is the thickness of the electrolyte, S is the area of the stainless steel sheet at room temperature, and R.sub.b is the measured bulk impedance. The solid polymer electrolyte was tested to have an ionic conductivity of 9.2×10.sup.−5 S/cm at 25° C.

[0054] The electrochemical window of the all-solid-state plastic crystal polymer electrolyte was tested: a stainless steel sheet and a sodium sheet were used as working electrode and reference electrode respectively, and the electrolyte was sandwiched between them and placed in 2032 battery case. The electrochemical window of electrolyte was measured by linear sweep voltammetry in the electrochemical workstation, the test temperature was 25° C., the starting potential was 2.0V, the highest potential was 6.0V, and the scanning speed was 0.5 mV/s. The electrochemical window of the all-solid-state plastic crystal polymer electrolyte was tested to be 4.8 V.

[0055] The sodium ion migration number of the all-solid-state plastic crystal polymer electrolyte was tested:

[0056] The electrolyte film was sandwiched between two sodium sheets, and the sodium ion migration number was measured by electrochemical AC impedance combined with DC polarization. The sodium ion migration number of the electrolyte was calculated by the formula

[00002]$t_{{\mathrm{Na}}^{+}}=\frac{I_s{R}_f\left(\Delta V-I_0{R}_I^0\right)}{I_0{R}_i\left(\Delta V-J_s{R}_I^s\right)}.$

Among them, ΔV is the DC voltage applied to both sides of the electrode, I.sub.0 and I.sub.s are the initial and stabilized current values, respectively, R.sub.i and R.sub.f are the initial and polarized impedances of the electrolyte film, and R.sub.I.sup.0 and R.sub.I.sup.s are the initial and polarized interface impedances of the electrode e/electrolyte respectively. The solid-state polymer electrolyte was tested to have a sodium ion migration number of 0.67 at 25° C.

[0057] 2. In-Situ Preparation of the Sodium Ion Battery Composite Electrode

[0058] Preparation of the composite positive/negative electrode: sodium carboxymethyl cellulose was dissolved in N,N-2-methylpyrrolidone at a concentration of 0.1 mol/L. Then, the positive electrode active material sodium vanadium phosphate [Na.sub.3V.sub.2(PO.sub.4).sub.3]/ negative electrode active material molybdenum disulfide (MoS.sub.2), binder sodium carboxymethyl cellulose and conductive agent acetylene black were mixed in a mass ratio of 7:2:1 and ground for at least 1 hour. The slurry obtained from the previous steps was evenly coated on the aluminum foil, vacuum dried and then cut according to the size. Next, the cut electrode sheet was immersed in the above mixture solution 2 to allow the reaction precursor solution to enter the inside of the electrode, and finally the electrode sheet was taken out and placed under an ultraviolet lamp for ultraviolet curing to obtain the final composite positive/negative electrode.

[0059] The composite Na.sub.3V.sub.2(PO.sub.4).sub.3 electrode prepared above was used as the positive electrode and the composite MoS.sub.2 was used as the negative electrode, the plastic crystal polymer electrolyte was assembled into the all-solid-state sodium battery, and this embodiment was measured with the LAND battery charging and discharging instrument. The all-solid-state sodium battery assembled with this plastic crystal polymer electrolyte was tested to have a current density of 0.2 A/g and a discharge specific capacity of 84 mAh/g at room temperature.

Embodiment 3

[0060] 1. Preparation of an all-Solid-State Plastic Crystal Polymer Electrolyte Film

[0061] A certain amount of sodium bis(trifluoromethylsulfonylimine) (NaTFSI) was weighed and added to succinonitrile (SN), and the mixture was heated and stirred to form a transparent and uniform NaTFSI salt solution 1 of succinonitrile, in which the concentration of NaTFSI in SN was 0.25 mol/L. Then a certain amount of B-crosslinker (n=20) was added to the solution 1, and a certain mass fraction of 1173 photoinitiator was added to the system at the same time, and stirring was continued to make a homogeneous solution 2. In the solution 2, the mass fraction of B-crosslinker (n=20) was 8 wt. %, and the content of photoinitiator 1173 was 0.5 wt. % of the mass of active monomer B-crosslinker (n=20). Then, the mixed solution was injected to the cellulose film support material, and after the solution was completely immersed, the nonwoven fabric containing the mixed solution was sandwiched between two clean glass sheets, and was cured into a film by ultraviolet curing technology, so that the final all-solid-state plastic crystal polymer electrolyte was obtained.

[0062] The ionic conductivity of the all-solid-state plastic crystal polymer electrolyte was tested:

[0063] The electrolyte film was sandwiched between two stainless steel sheets and placed in a 2032 battery case, and then the ionic conductivity of the electrolyte was measured by electrochemical AC impedance spectroscopy, and the ionic conductivity was calculated by the formula: σ=d/SR.sub.b, where, d is the thickness of the electrolyte, S is the area of the stainless steel sheet at room temperature, and R.sub.b is the measured bulk impedance. The solid polymer electrolyte was tested to have an ionic conductivity of 1.32×10.sup.−4 S/cm at 25° C.

[0064] The electrochemical window of the all-solid-state plastic crystal polymer electrolyte was tested: the stainless steel sheet and the sodium sheet were used as working electrode and reference electrode respectively, and the electrolyte was sandwiched between them and placed in 2032 battery case. The electrochemical window of electrolyte was measured by linear sweep voltammetry in the electrochemical workstation, the test temperature was 25° C., the starting potential was 2.0V, the highest potential was 6.0V, and the scanning speed was 0.5 mV/s. The electrochemical window of the all-solid-state plastic crystal polymer electrolyte was tested to be 4.3 V.

[0065] The sodium ion migration number of the all-solid-state plastic crystal polymer electrolyte was tested:

[0066] The electrolyte film was sandwiched between two sodium sheets, and the sodium ion migration number was measured by electrochemical AC impedance combined with DC polarization. The sodium ion migration number of the electrolyte was calculated by the formula

[00003]$t_{{\mathrm{Na}}^{+}}=\frac{I_s{R}_f\left(\Delta V-I_0{R}_I^0\right)}{I_0{R}_i\left(\Delta V-J_s{R}_I^s\right)}.$

Among them, ΔV is the DC voltage applied to both sides of the electrode, I.sub.0 and I.sub.s are the initial and stabilized current values, respectively, R.sub.i and R.sub.f are the initial and polarized impedances of the electrolyte film, R.sub.I.sup.0 and R.sub.I.sup.s are the initial and polarized interface impedances of the electrode e/electrolyte, respectively. The all-solid-state polymer electrolyte was tested to have a sodium ion migration number of 0.40 at 25° C.

[0067] 2. In-Situ Preparation of the Sodium Ion Battery Composite Electrode

[0068] Preparation of the composite positive electrode: the binder sodium alginate was dissolved in N,N-2-methylpyrrolidone at a concentration of 0.1 mol/L. Then, the positive electrode active material Prussian blue, binder sodium alginate and conductive agent Ketjen carbon were mixed in a mass ratio of 6:2:2 and ground for at least 1 hour. The slurry obtained from the previous steps was evenly coated on the aluminum foil, vacuum dried and then cut according to the size. Next, the cut electrode sheet was immersed in the above mixture solution 2 to allow the reaction precursor solution to enter the inside of the electrode, and finally the electrode sheet was taken out and placed under an ultraviolet lamp for ultraviolet curing to obtain the final composite positive electrode. In this embodiment, the negative electrode adopted a metal sodium sheet.

[0069] The composite Prussian blue electrode prepared above was used as the positive electrode and the sodium metal was used as the negative electrode, the plastic crystal polymer electrolyte was assembled into an all-solid-state sodium battery, and this embodiment was measured with a LAND battery charging and discharging instrument. The all-solid-state sodium battery assembled with this plastic crystal polymer electrolyte was tested to have a discharge specific capacity of 92.0 mAh/g at room temperature.

Comparative Embodiment 1

[0070] 1. Preparation of a Boron-Free all-Solid-State Plastic Crystal Polymer Electrolyte Film

[0071] A certain amount of sodium perchlorate (NaClO.sub.4) was weighed and added to succinonitrile (SN), and the mixture was heated and stirred to form a transparent and uniform NaClO.sub.4 salt solution 1 of succinonitrile, in which the concentration of NaClO.sub.4 in SN was 1 mol/L. Then a certain amount of ETPTA crosslinker was added to the solution 1, and a certain mass fraction of 1173 photoinitiator was added to the system at the same time, and stirring was continued to make a homogeneous solution 2. In the solution 2, a mass fraction of ETPTA was 12 wt. %, and a content of photoinitiator 1173 was 1 wt. % of the mass of active monomer ETPTA. Then, the mixed solution was injected to the polypropylene-cellulose composite nonwoven fabric, and after the solution was completely immersed, the nonwoven fabric containing the mixed solution was sandwiched between two clean glass sheets, and was cured into a film by ultraviolet curing technology, so that the final boron-free all-solid-state plastic crystal polymer electrolyte was obtained, marked as C-PCPE.

[0072] The ionic conductivity of the boron-free all-solid-state plastic crystal polymer electrolyte was tested:

[0073] The electrolyte film was sandwiched between two stainless steel sheets and placed in a 2032 battery case, and then the ionic conductivity of the electrolyte was measured by electrochemical AC impedance spectroscopy, and the ionic conductivity was calculated by the formula: σ=d/SR.sub.b, where, d is the thickness of the electrolyte, S is the area of the stainless steel sheet at room temperature, and R.sub.b is the measured bulk impedance. The solid-state polymer electrolyte was tested to have an ionic conductivity of 4.0×10.sup.−4 S/cm at 25° C.

[0074] The electrochemical window of the boron-free all-solid-state plastic crystal polymer electrolyte was tested: a stainless steel sheet and a sodium sheet were used as working electrode and reference electrode respectively, and the electrolyte was sandwiched between them and placed in 2032 battery case. The electrochemical window of electrolyte was measured by linear sweep voltammetry in an electrochemical workstation, the test temperature was 25° C., the starting potential was 2.0V, the highest potential was 6.0V, and the scanning speed was 0.5 mV/s. The electrochemical window of the all-solid-state plastic crystal polymer electrolyte was tested to be 4.5 V.

[0075] The sodium ion migration number of the boron-free all-solid-state plastic crystal polymer electrolyte was tested:

[0076] The electrolyte film was sandwiched between two sodium sheets, and the sodium ion migration number was measured by electrochemical AC impedance combined with DC polarization. The sodium ion migration number of the electrolyte was calculated by the formula

[00004]$t_{{\mathrm{Na}}^{+}}=\frac{I_s{R}_f\left(\Delta V-I_0{R}_I^0\right)}{I_0{R}_i\left(\Delta V-J_s{R}_I^s\right)}.$

Among them, ΔV is the DC voltage applied to both sides of the electrode, I.sub.0 and I.sub.s are the initial and stabilized current values, respectively, R.sub.i and R.sub.f are the initial and polarized impedances of the electrolyte film, R.sub.I.sup.0 and R.sub.I.sup.s are the initial and polarized interface impedances of the electrode e/electrolyte, respectively. The all-solid-state polymer electrolyte was tested to have a sodium ion migration number of 0.26 at 25° C.

[0077] 2. In-Situ Preparation of a Sodium Ion Battery Composite Electrode

[0078] Preparation of a composite positive/negative electrode: polyvinylidene fluoride (PVdF) was dissolved in N,N-2-methylpyrrolidone at a concentration of 0.1 mol/L. Then the positive electrode active material layered oxide Na.sub.1/3Fe.sub.1/3Mn.sub.1/3O.sub.2/ negative electrode active material hard carbon, binder PVdF, and conductive agent Super P were mixed in a mass ratio of 8:1:1 and ground for at least 2 hours. The slurry obtained from the previous step was evenly coated on the aluminum foil, vacuum dried and then cut according to the size. Next, the cut electrode sheet was immersed in the above mixture solution 2 to allow the reaction precursor solution to enter the inside of the electrode, and finally the electrode sheet was taken out and placed under an ultraviolet lamp for ultraviolet curing to obtain the final composite positive/composite negative electrode.

[0079] The composite Na.sub.1/3Fe.sub.1/3Mn.sub.1/3O.sub.2/ electrode prepared above was used as the positive electrode and the composite hard carbon was used as the negative electrode, boron-free plastic crystal polymer electrolyte was assembled into the all-solid-state sodium battery, and this embodiment was measured with a LAND battery charging and discharging instrument. The discharge specific capacity of the all-solid-state sodium battery assembled with this plastic crystal polymer electrolyte was tested to be 101.2 mAh/g at room temperature, but as the number of cycles increased, the capacity decreased significantly, and after 80 cycles, the capacity retention rate was less than 65% (FIG. 1); and the all-solid-state sodium ion battery assembled with this boron-free plastic crystal all-solid-state polymer electrolyte had poor rate performance, with a low discharge capacity of 48.1 mAh/g at current density of 0.5 A/g (FIG. 3).

Comparative Embodiment 2

[0080] Preparation of an all-Solid-State Plastic Crystal Polymer Electrolyte Film

[0081] A certain amount of NaClO.sub.4 was weighed and added to succinonitrile (SN), and the mixture was heated and stirred to form a transparent and uniform NaClO.sub.4 salt solution 1 of succinonitrile, in which the concentration of NaClO.sub.4 in SN was 2 mol/L. Then a certain amount of B-HEMA crosslinker was added to the solution 1, and a certain mass fraction of 1173 photoinitiator was added to the system at the same time, and stirring was continued to make a homogeneous solution 2. In the solution 2, a mass fraction of B-HEMA was 35 wt. %, and a content of photoinitiator 1173 was 0.5 wt. % of the mass of active monomer B-HEMA. Then, the mixed solution was injected to the cellulose support material, and after the solution was completely immersed, the nonwoven fabric containing the mixed solution was sandwiched between two clean glass sheets, and was cured into a film by ultraviolet curing technology, so that the final all-solid-state plastic crystal polymer electrolyte was obtained.

[0082] The ionic conductivity of the all-solid-state plastic crystal polymer electrolyte was tested:

[0083] The electrolyte film was sandwiched between two stainless steel sheets and placed in a 2032 battery case, and then the ionic conductivity of the electrolyte was measured by electrochemical AC impedance spectroscopy, and the ionic conductivity was calculated by the formula: σ=d/SR.sub.b, where, d is the thickness of the electrolyte, S is the area of the stainless steel sheet at room temperature, and R.sub.b is the measured bulk impedance. The all-solid-state polymer electrolyte was tested to have a very low ionic conductivity of 9.4×10 S/cm at 25° C.

[0084] The electrochemical window of the all-solid-state plastic crystal polymer electrolyte was tested: a stainless steel sheet and a sodium sheet were used as working electrode and reference electrode respectively, and the electrolyte was sandwiched between them and placed in 2032 battery case. The electrochemical window of electrolyte was measured by linear sweep voltammetry in an electrochemical workstation, the test temperature was 25° C., the starting potential was 2.0V, the highest potential was 6.0V, and the scanning speed was 0.5 mV/s. The electrochemical window of the all-solid-state plastic crystal polymer electrolyte was tested to be 4.4 V.

[0085] The sodium ion migration number of the all-solid-state plastic crystal polymer electrolyte was tested.

[0086] The electrolyte film was sandwiched between two sodium sheets, and the sodium ion migration number was measured by electrochemical AC impedance combined with DC polarization. The sodium ion migration number of the electrolyte was calculated by the formula

[00005]$t_{{\mathrm{Na}}^{+}}=\frac{I_s{R}_f\left(\Delta V-I_0{R}_I^0\right)}{I_0{R}_i\left(\Delta V-J_s{R}_I^s\right)}.$

Among them, ΔV is the DC voltage applied to both sides of the electrode, I.sub.0 and I.sub.s are the initial and stabilized current values, respectively, R.sub.i and R.sub.f are the initial and polarized impedances of the electrolyte film, R.sub.I.sup.0 and R.sub.I.sup.s are the initial and polarized interface impedances of the electrode e/electrolyte, respectively. The all-solid-state polymer electrolyte was tested to have a sodium ion migration number of 0.69 at 25° C.

[0087] Due to the low ionic conductivity of the plastic crystal polymer electrolyte prepared in this comparative embodiment at room temperature, the assembled all-solid-state battery cannot be charged and discharged at room temperature, no later experiments were performed.

Comparative Embodiment 3

[0088] Preparation of an all-Solid-State Plastic Crystal Polymer Electrolyte Film

[0089] A certain amount of NaTf was weighed and added to succinonitrile (SN), and the mixture was heated and stirred to form a transparent and uniform NaTf salt solution 1 of succinonitrile, in which the concentration of NaTf in SN was 0.2 mol/L. Then a certain amount of B-crosslinker (n=6) was added to the solution 1, and a certain mass fraction of 1173 photoinitiator was added to the system at the same time, and stirring was continued to make a homogeneous solution 2. In the solution 2, a mass fraction of B-crosslinker (n=6) was 5 wt. %, and a content of photoinitiator 1173 was 1 wt. % of the mass of active monomer B-crosslinker (n=6). Then, the mixed solution was injected to the cellulose support material, and after the solution was completely immersed, the nonwoven fabric containing the mixed solution was sandwiched between two clean glass sheets, and was cured into a film by ultraviolet curing technology, so that the final all-solid-state plastic crystal polymer electrolyte was obtained.

[0090] The ionic conductivity of the all-solid-state plastic crystal polymer electrolyte was tested:

[0091] The electrolyte film was sandwiched between two stainless steel sheets and placed in a 2032 battery case, and then the ionic conductivity of the electrolyte was measured by electrochemical AC impedance spectroscopy, and the ionic conductivity was calculated by the formula: σ=d/SR.sub.b, where, d is the thickness of the electrolyte, S is the area of the stainless steel sheet at room temperature, and R.sub.b is the measured bulk impedance. The all-solid-state polymer electrolyte was tested to have a very low ionic conductivity of 1.2×10.sup.−5 S/cm at 25° C. The electrochemical window of the all-solid-state plastic crystal polymer electrolyte was tested: a stainless steel sheet and a sodium sheet were used as working electrode and reference electrode respectively, and the electrolyte was sandwiched between them and placed in 2032 battery case. The electrochemical window of electrolyte was measured by linear sweep voltammetry in an electrochemical workstation, the test temperature was 25° C., the starting potential was 2.0V, the highest potential was 6.0V, and the scanning speed was 0.5 mV/s. The electrochemical window of the all-solid-state plastic crystal polymer electrolyte was tested to be 3.8 V.

[0092] The sodium ion migration number of the all-solid-state plastic crystal polymer electrolyte was tested.

[0093] The electrolyte film was sandwiched between two sodium sheets, and the sodium ion migration number was measured by electrochemical AC impedance combined with DC polarization. The sodium ion migration number of the electrolyte was calculated by the formula

[00006]$t_{{\mathrm{Na}}^{+}}=\frac{I_s{R}_f\left(\Delta V-I_0{R}_I^0\right)}{I_0{R}_i\left(\Delta V-J_s{R}_I^s\right)}.$

Among them, ΔV is the DC voltage applied to both sides of the electrode, I.sub.0 and I.sub.s are the initial and stabilized current values, respectively, R.sub.i and R.sub.f are the initial and polarized impedances of the electrolyte film, R.sub.I.sup.0 and R.sub.I.sup.s are the initial and polarized interface impedances of the electrode e/electrolyte, respectively. The all-solid-state polymer electrolyte was tested to have a sodium ion migration number of 0.29 at 25° C.

[0094] Due to the low ionic conductivity of the plastic crystal polymer electrolyte prepared in this comparative embodiment at room temperature, the narrow electrochemical window, the assembled all-solid-state battery cannot be charged and discharged at room temperature, no later experiments were performed.