CN117913399A - Method for inhibiting sodium precipitation of battery cathode by electrolyte optimized superposition step charging - Google Patents
Method for inhibiting sodium precipitation of battery cathode by electrolyte optimized superposition step charging Download PDFInfo
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Abstract
The invention provides a method for inhibiting sodium precipitation of a battery cathode by electrolyte optimized superposition step charging, which solves the problems that the polarization slowing down range is smaller, the sodium precipitation risk still exists, the sodium precipitation inhibition control is difficult to realize and the like when sodium precipitation of a hard carbon cathode of a sodium ion battery is inhibited at present. The method comprises the following steps: selecting reference electrode, quasi-reference electrode and positive electrode material to construct a three-electrode soft-package battery cell; charging the battery cell to a full state, and determining thermodynamic sodium precipitation voltage by a negative electrode sodium embedding curve; charging the three-electrode soft package battery core to different charge states to obtain dynamic sodium precipitation voltage; dividing a step charging interval according to thermodynamic sodium precipitation voltage and kinetic sodium precipitation voltage, and formulating a step charging strategy; according to the strategy, the battery cell is charged to a full state under the condition of unequal electrolyte injection quantity, and the optimization method for inhibiting the sodium precipitation of the hard carbon negative electrode by step charging is obtained. By constructing the three-electrode soft-package battery cell, the injection amount of the electrolyte is controlled to perform step charging, so that sodium precipitation degrees of different hard carbon cathodes are reduced, and the three-electrode soft-package battery cell has the advantages of convenience in control, high reliability and the like.
Description
Technical Field
The invention relates to the technical field of sodium ion batteries, in particular to a method for inhibiting sodium precipitation of a battery cathode by electrolyte optimized superposition step charging.
Background
In recent years, the development of sodium ion battery technology is accelerated in various countries in the world. The negative electrode materials of the sodium ion battery at present mainly comprise carbon-based negative electrodes, titanium-based negative electrodes, alloy negative electrodes, phosphorus/sulfide and organic materials. The hard carbon in the carbon-based negative electrode material has the characteristics of simple production process, abundant precursors, abundant sodium storage sites, low cost and the like, and is the material with the highest practical value and closest industrialization at present.
However, for a hard carbon negative electrode material, there is a risk of precipitation of sodium when the intercalation potential is close to the precipitation potential of metallic sodium 0V (vs. Na +/Na) during charging. The impedance of a hard carbon anode changes with its charge state, resulting in a change in its degree of polarization. Under the low charge state, the polarization of the hard carbon cathode is smaller, and the potential of the hard carbon cathode is more forward biased to isolate sodium potential. Under a high charge state, the polarization of the hard carbon cathode is larger, and the potential of the hard carbon cathode is closer to the sodium precipitation potential. If the hard carbon negative electrode is charged continuously at high multiplying power under different charge states, the polarization degree is aggravated, and sodium precipitation occurs earlier.
In order to avoid sodium precipitation of the hard carbon negative electrode of the sodium ion battery in the charging process, charging intervals are divided, stepped charging is used, charging with different multiplying powers is used in different intervals, and the excessively fast polarization of the hard carbon negative electrode can be controlled. However, no suitable strategy is found for dividing the intervals by using any parameters and selecting how large multiplying power is used for different intervals.
Furthermore, although the increase speed of hard carbon polarization can be effectively restrained by using the step charge, the polarization slowing range is smaller, and the risk of sodium precipitation still exists in the long-term charge-discharge cycle process of the battery. The injection amount of the electrolyte is optimized to improve the infiltration uniformity of the hard carbon cathode in the electrolyte, so that the diffusion speed of sodium ions in the electrolyte can be increased, the impedance of the pole piece can be reduced, and the polarization slowing amplitude of the pole piece in the charging process can be increased. However, for hard carbon materials with different sources, an appropriate scheme is not found for improving the injection amount of electrolyte with adaptive sodium storage kinetics performance.
The invention discloses a modified carbon negative pole piece for inhibiting sodium precipitation and a preparation method and application thereof, wherein the publication number of the modified carbon negative pole piece is CN 116825960A; the bulk phase modification is to add a functional coating material as an additive into slurry for preparing the original carbon negative electrode to form composite slurry, and the composite slurry is molded on a current collector to prepare the bulk phase modified carbon negative electrode plate. The main material of the functional coating material is selected from nano porous organic frame material or inorganic nano metal oxide, and the method effectively inhibits the sodium precipitation phenomenon of the negative electrode of the carbon negative electrode in the charging and discharging process of the sodium ion battery, but mainly inhibits the sodium precipitation through physical modification of the negative electrode material, so that the control of the sodium precipitation inhibition is difficult.
Disclosure of Invention
The invention aims to solve the problems that the polarization slowing down amplitude is small, the sodium precipitation risk still exists, the sodium precipitation control is difficult to realize when the sodium precipitation of the hard carbon negative electrode of the sodium ion battery is inhibited at present.
The technical problems are solved by the following technical scheme: a method for inhibiting sodium precipitation of a battery cathode by electrolyte optimization and superposition step charging comprises the following steps:
S1, selecting a reference electrode and a quasi-reference electrode and a positive electrode material matched with a hard carbon negative electrode material to construct a three-electrode soft-package battery cell;
s2, charging the three-electrode soft package battery cell to a full state at a certain charging multiplying power to obtain a negative electrode sodium embedding curve, and determining thermodynamic sodium precipitation voltage according to the negative electrode sodium embedding curve;
S3, charging the three-electrode soft package battery core to different charge states at a certain charging multiplying power, and defining the full battery terminal voltage corresponding to the sodium precipitation of the hard carbon negative electrode as dynamic sodium precipitation voltage;
And S4, dividing a step charging interval according to the thermodynamic sodium precipitation voltage and the kinetic sodium precipitation voltage, making a step charging strategy, and charging the battery cell to a full state under the condition of unequal electrolyte injection quantity to obtain the optimization method for inhibiting the sodium precipitation of the hard carbon negative electrode by step charging.
The thermodynamic sodium precipitation voltage and the kinetic sodium precipitation voltage are taken as the division basis of the step charging interval, a step charging strategy is formulated, the increase speed of hard carbon polarization can be effectively restrained, the battery cell is charged under the condition of unequal electrolyte injection quantity, the infiltration uniformity of the hard carbon cathode in the electrolyte is improved, and the sodium precipitation degree in the long-term charging and discharging cycle process of the battery is slowed down.
Preferably, in step S4, the step charging strategy includes: charging the three-electrode soft package battery core with a charging rate of not less than 0.5 ℃ until the battery core voltage reaches the thermodynamic sodium precipitation voltage; after the cell voltage reaches the thermodynamic sodium precipitation voltage, adjusting the charging multiplying power to be within the range of 0.1-0.4C, and recharging until the cell voltage reaches the thermodynamic sodium precipitation voltage; and after the cell voltage reaches the kinetic sodium precipitation voltage, charging the three-electrode soft-package cell to a full-charge state at a charging rate smaller than 0.1 ℃. The impedance of the carbon negative electrode changes with the charge state, and thus the polarization degree of the carbon negative electrode changes. The polarization of the hard carbon cathode is smaller in the low-charge state, and the potential of the hard carbon cathode is more in positive bias sodium isolation potential; the polarization of the hard carbon cathode is larger under the high charge state, and the potential of the hard carbon cathode is closer to the sodium precipitation potential. Therefore, the phenomenon of aggravation of polarization degree can be relieved by charging according to different charge states of the hard carbon negative electrode with proper charging multiplying power, and the early occurrence of sodium precipitation can be effectively restrained.
Preferably, in step S4, the method for obtaining the step charge inhibition hard carbon negative electrode sodium precipitation optimization includes: and (3) according to a step charging interval divided by a step charging strategy, charging the battery core to a full state by using electrolyte injection amounts with unequal electrolyte injection amounts, disassembling the battery core after charging, and selecting an optimization mode for inhibiting sodium precipitation of the hard carbon negative electrode by step charging according to the sodium precipitation degree of the hard carbon negative electrode. According to a formulated step charging strategy, battery cells are charged under different electrolyte injection amounts, and a method for inhibiting sodium precipitation of hard carbon negative electrodes of the sodium ion battery by optimally overlapping the step charging of the electrolyte can be prepared aiming at soft package cells of the sodium ion battery assembled by hard carbon negative electrode materials with different sources.
Preferably, in step S4, the unequal electrolyte injection amount is between 1.1 and 2 times the normal electrolyte injection amount. Optimizing the injection amount of the electrolyte can improve the infiltration uniformity of the hard carbon cathode in the electrolyte, can improve the diffusion speed of sodium ions in the electrolyte and reduce the impedance of the pole piece, thereby improving the polarization slowing down amplitude of the pole piece in the charging process.
Preferably, the normal electrolyte injection amount is an electrolyte injection amount when the three-electrode pouch cell capacity is 1 Ah.
Preferably, in step S1, the reference electrode comprises metallic sodium, the quasi-reference electrode comprises metallic platinum, and the positive electrode material comprises layered oxide and polyanion compound and prussian blue and prussian white.
Preferably, in step S1, the hard carbon anode material includes hard carbon prepared with biomass-based and high molecular species and resin-based and coal-based species as precursors.
Preferably, in step S2, the thermodynamic sodium precipitation voltage is a full cell terminal voltage corresponding to a negative electrode potential of 0V (vs. na+/Na) or negative electrode potential of-2V (vs. pt) on the negative electrode sodium intercalation curve.
The beneficial effects of the invention are as follows: in-situ monitoring of the change of the hard carbon negative electrode potential and the battery terminal voltage in the charging process is realized by a three-electrode soft-package battery core mode, so that accurate and reliable basis is provided for dividing the step charging interval; and through electrolyte optimization, stacked ladder charging, the risk of sodium precipitation of different hard carbon cathodes is further reduced.
Drawings
Fig. 1 is a flow chart of the method of the present invention.
Fig. 2 is an in-situ recording chart of the electric potential of a three-electrode soft package battery cell under the 4C magnification in the third embodiment.
Detailed Description
Embodiment one: the embodiment provides a method for inhibiting sodium precipitation of a battery cathode by electrolyte optimization superposition step charging, which comprises the following steps in combination with fig. 1:
S1, selecting a reference electrode and a quasi-reference electrode and a positive electrode material matched with a hard carbon negative electrode material to construct a three-electrode soft-package battery cell;
s2, charging the three-electrode soft package battery cell to a full state at a certain charging multiplying power to obtain a negative electrode sodium embedding curve, and determining thermodynamic sodium precipitation voltage according to the negative electrode sodium embedding curve;
S3, charging the three-electrode soft package battery core to different charge states at a certain charging multiplying power, and defining the full battery terminal voltage corresponding to the sodium precipitation of the hard carbon negative electrode as dynamic sodium precipitation voltage;
And S4, dividing a step charging interval according to the thermodynamic sodium precipitation voltage and the kinetic sodium precipitation voltage, making a step charging strategy, and charging the battery cell to a full state under the condition of unequal electrolyte injection quantity to obtain the optimization method for inhibiting the sodium precipitation of the hard carbon negative electrode by step charging.
In S1, using metallic sodium as a reference electrode or metallic platinum as a quasi-reference electrode, using any one of layered oxide, polyanion compound, prussian blue and Prussian white as a positive electrode material, matching hard carbon negative electrode materials with different sources on the market, and using the metallic sodium reference electrode or the metallic platinum quasi-reference electrode to construct a three-electrode soft-package battery core.
In S2, the three-electrode soft-package battery cell is charged to a full state with a certain multiplying power, the charging multiplying power is 0.5C or more, including 0.5C, 1C, 1.5C, 2C, 3C and 4C, a three-electrode soft-package full-battery charging curve, a positive electrode sodium removing curve and a hard carbon negative electrode sodium embedding curve are obtained, and a full-battery terminal voltage corresponding to a negative electrode potential of 0V (vs. na+/Na) or-2V (vs. pt) is obtained through the negative electrode sodium embedding curve, and is defined as a thermodynamic sodium precipitation voltage U 1.
In S3, charging the three-electrode soft package battery core with a certain multiplying power to different charge states, adjusting the charging multiplying power to 0.1C-0.4C including 0.1C, 0.2C, 0.3C and 0.4C, charging until the battery terminal voltage reaches U 2, and disassembling the battery core to obtain the full battery terminal voltage corresponding to the hard carbon negative electrode when sodium precipitation occurs, and defining the full battery terminal voltage as dynamic sodium precipitation voltage U 2.
In S4, the step charge strategy includes: charging the three-electrode soft package battery core with a charging rate of not less than 0.5 ℃ until the battery core voltage reaches the thermodynamic sodium precipitation voltage; after the cell voltage reaches the thermodynamic sodium precipitation voltage, adjusting the charging multiplying power to be within the range of 0.1-0.4C, and recharging until the cell voltage reaches the thermodynamic sodium precipitation voltage; and after the cell voltage reaches the kinetic sodium precipitation voltage, charging the three-electrode soft-package cell to a full-charge state at a charging rate smaller than 0.1 ℃.
The method for obtaining the optimization method for inhibiting sodium precipitation of the hard carbon negative electrode by step charging comprises the following steps: and (3) according to a step charging interval divided by a step charging strategy, charging the battery core to a full state by using electrolyte injection amounts with unequal electrolyte injection amounts, disassembling the battery core after charging, and selecting an optimization mode for inhibiting sodium precipitation of the hard carbon negative electrode by step charging according to the sodium precipitation degree of the hard carbon negative electrode. The injection amount of the unequal electrolyte is 1.1 times to 2 times of the injection amount of the normal electrolyte. The normal electrolyte injection amount is the electrolyte injection amount when the capacity of the three-electrode soft package battery cell is 1 Ah.
Embodiment two: the embodiment provides a specific method for constructing a three-electrode soft-package battery cell, namely, the manufacturing of the three-electrode sodium ion soft-package battery cell specifically adopts the following technical means: and (3) manufacturing a metal sodium reference electrode: taking an aluminum tab belt with tab glue at the upper end, wherein the middle is insulated by a height Wen Jiaotie, and the aluminum belt at the tail end is 3mm long and 1mm wide under the general condition. The terminal aluminum strip is wrapped by a sodium sheet or a sodium strip, so that the aluminum sheet is tightly attached to sodium. And finally, wrapping the middle insulating layer and the end sodium sheets or sodium bands by using a polypropylene PP diaphragm, and completing the manufacture of the reference electrode.
Manufacturing a three-electrode soft package battery cell: the positive electrode material of the sodium ion battery is fixed, and the positive electrode material of the sodium ion battery can be any one of layered oxide, polyanion compound, prussian blue or Prussian white, and is matched with hard carbon negative electrode materials with different sources on the market, such as hard carbon negative electrode materials named HC-1, HC-2, HC-3, HC-4 and the like, wherein the number of the materials is generally 7 for the positive electrode, 8 for the negative electrode, and the materials are laminated. After lamination is completed, the tab is welded and high-temperature glue is pasted, and then the battery cell is transferred to a glove box. The metal sodium reference electrode wrapped with the diaphragm is plugged into the cell, and the reference electrode should be close to the working electrode as much as possible, the current negative electrode is the working electrode, the current negative electrode is placed on one side close to the positive electrode plate, and the top end is sealed with the adhesive tape. And then, the battery cell is filled into an aluminum plastic film. In the glove box, the sides and top of the cell were heat sealed first. Then the electrolyte is injected from the unheated end cap. After the liquid injection is finished, the liquid injection end is heat-sealed and placed for a proper time, so that the electrolyte is ensured to fully infiltrate the pole piece. And finally, transferring the battery cell out, and performing secondary heat sealing. After the heat sealing is finished, the battery cell is transferred into a 45 ℃ incubator for aging to finish the manufacturing of the three-electrode soft package battery cell.
Embodiment III: the embodiment provides a specific determination method for thermodynamic sodium precipitation voltage, which adopts the following technical means: the manufacturing method of the metal sodium reference electrode is the same as that of the second embodiment; when the three-electrode soft package battery core is manufactured: the positive electrode material was layered oxide, the hard carbon negative electrode was HC-1, and the other portions were the same as in example two.
Regarding the setting of the charging system, different charging rates can be used according to practical application conditions, in this embodiment, the battery core is formed first, and then the battery core is charged to 100% soc by using 0.5C, 1C, and 4C rates.
Determination of different hard carbon negative electrode thermodynamic sodium precipitation terminal voltages U 1: and a multichannel data recorder is used for connecting the anode-cathode, the anode-reference electrode and the cathode-reference electrode, and meanwhile, the battery performance test cabinet is connected with the anode and the cathode of the three-electrode battery, and the change of potential is monitored in situ in the charging process. Recording the terminal voltage of the corresponding battery when the hard carbon negative electrode reaches the thermodynamic sodium precipitation potential 0V (vs. Na +/Na), wherein the terminal voltage is U 1, and fig. 2 is an in-situ record chart of the potential of a three-electrode soft-package battery core under the 4C multiplying power, and the record results are shown in the following table 1:
| Multiplying power | Thermodynamic sodium precipitation terminal voltage U 1 (V) |
| 0.5C | 3.561 |
| 1C | 3.423 |
| 4C | 2.913 |
TABLE 1 hard carbon negative electrode thermodynamic sodium precipitation terminal voltage U at different charging rates 1
Embodiment four: the embodiment provides a method for determining kinetic sodium precipitation voltage, which specifically adopts the following technical means:
The sodium metal reference electrode was prepared in the same manner as in example two. When the three-electrode soft-package battery core is manufactured, the layered oxide is used as the positive electrode material, HC-1 is used as the hard carbon negative electrode, and the other parts are the same as those in the second embodiment.
Regarding the setting of the charging regime, the cells were charged to 50%, 65%, 75% and 100% states of charge (SOC) using 0.05C, 0.5C, 1C, respectively.
Determination of different hard carbon negative electrode kinetics sodium end voltages U 2: and (3) connecting the positive electrode with the negative electrode, connecting the positive electrode with the reference electrode with the negative electrode with the reference electrode by using a multichannel data recorder, and simultaneously connecting the positive electrode with the negative electrode of the three-electrode battery by using a battery performance test cabinet, and respectively charging the battery cells to 50%, 65%, 75% and 100% of charging states by using 0.05C, 0.5C and 1C. After the charging is finished, the battery cell is disassembled, the sodium precipitation degree of the hard carbon negative electrode under different multiplying powers and different charging states and the corresponding battery terminal voltage when sodium precipitation starts to occur are analyzed, and the results are shown in table 2. As can be seen from table 2, using different charging rates, 75% SOC is the node at which hard carbon negative electrode sodium precipitation starts, and the corresponding battery terminal voltage is about 3.6V, 3.6V can be defined as hard carbon negative electrode kinetic sodium precipitation terminal voltage U 2.
TABLE 2 sodium precipitation of hard carbon negative electrode under different SOC conditions with different multiplying powers and battery terminal voltage
Fifth embodiment: the embodiment provides a formulation mode of a ladder charging strategy, which is provided with a plurality of comparison examples, and specifically adopts the following technical means:
The sodium ion soft-package battery core is manufactured, the positive electrode material is layered oxide, the hard carbon negative electrode is HC-1, the reference electrode is not implanted, and other parts are the same as the method in the second embodiment.
Making a ladder charging strategy: according to the thermodynamic sodium precipitation voltage U 1 determined in example three and the kinetic sodium precipitation voltage U 2 determined in example four, the step charge is divided into 3 intervals, and the following charge strategy is formulated according to the following steps:
Firstly, setting 1C multiplying power to charge the battery to a terminal voltage of U 1;
Secondly, setting 0.5C multiplying power to charge the battery to the voltage U 2;
and thirdly, setting the multiplying power of 0.05C to charge the battery to a full state.
To verify the feasibility of the full cell step charge strategy of this example, comparative examples 5-1, 5-2 were set for test comparison, wherein comparative examples 5-1, 5-2 used the same full cells as example five.
The charging strategy of comparative example 5-1 is: and setting the 1C multiplying power, and directly charging the battery to a full state.
The charging strategy of comparative example 5-2 is: and setting the multiplying power of 0.5C, and directly charging the battery to a full state.
The batteries were charged according to the charging strategies formulated in comparative example 5-1, comparative example 5-2 and example five, and after full charge, the cells were disassembled for hard carbon negative electrode sodium precipitation analysis. As can be seen from the comparison experiment results, the sodium precipitation of the hard carbon negative electrode is very serious when the charging strategy of comparative example 5-1 and the charging strategy of comparative example 5-2 are adopted. And when the step charging strategy of the fifth embodiment is used, the sodium precipitation degree of the hard carbon negative electrode is obviously improved.
Example six: the embodiment provides a formulation mode of an electrolyte optimization superposition step charging method for inhibiting sodium precipitation of a hard carbon negative electrode, which specifically adopts the following technical means:
the same full cell of example five was used, into which 1.2 times the normal electrolyte injection amount was injected, and charged using the step charge strategy described in example five.
Meanwhile, in order to verify the feasibility of the electrolyte optimizing and stacking step charging strategy in the embodiment, a comparative example 6-1 is set, wherein the comparative example 6-1 is a normal electrolyte injection amount, and the normal electrolyte injection amount is as follows: the sodium ion soft package battery core capacity is 1Ah, the injection amount of electrolyte is 4g, and the electrolyte is defined as normal injection amount E 0.
The battery was charged according to the charging strategy determined in this example and comparative example 6-1, respectively, and after full charge, the cell was disassembled for hard carbon negative electrode sodium analysis. The comparison result shows that when the injection amount of the electrolyte is increased to 1.2 times of the normal injection amount and a step charging system is overlapped, the sodium precipitation of the hard carbon negative electrode can be completely avoided.
Embodiment seven: the embodiment provides a method for inhibiting sodium precipitation of a battery cathode by electrolyte optimization superposition step charging, which comprises the following steps: s1, selecting a reference electrode and a quasi-reference electrode and a positive electrode material matched with a hard carbon negative electrode material to construct a three-electrode soft-package battery cell; s2, charging the three-electrode soft package battery cell to a full state at a certain charging multiplying power to obtain a negative electrode sodium embedding curve, and determining thermodynamic sodium precipitation voltage according to the negative electrode sodium embedding curve;
S3, charging the three-electrode soft package battery core to different charge states at a certain charging multiplying power, and defining the full battery terminal voltage corresponding to the sodium precipitation of the hard carbon negative electrode as dynamic sodium precipitation voltage;
And S4, dividing a step charging interval according to the thermodynamic sodium precipitation voltage and the kinetic sodium precipitation voltage, making a step charging strategy, and charging the battery cell to a full state under the condition of unequal electrolyte injection quantity to obtain the optimization method for inhibiting the sodium precipitation of the hard carbon negative electrode by step charging.
The reference electrode may be selected from a material comprising sodium metal and the quasi-reference electrode may be selected from a material comprising platinum metal. The positive electrode material comprises layered oxide, polyanion compound, prussian blue and Prussian white; the hard carbon anode material comprises hard carbon prepared by taking biomass-based and high-molecular and resin-based and coal-based materials as precursors.
The thermodynamic sodium precipitation voltage is generally the full cell terminal voltage corresponding to a negative electrode potential of 0V (vs. Na+/Na) or negative electrode potential of-2V (vs. Pt) on a negative electrode sodium intercalation curve.
The formulated step charging strategy specifically comprises the following steps: charging the three-electrode soft package battery core with a charging rate of not less than 0.5 ℃ until the battery core voltage reaches the thermodynamic sodium precipitation voltage; after the cell voltage reaches the thermodynamic sodium precipitation voltage, adjusting the charging multiplying power to be within the range of 0.1-0.4C, and recharging until the cell voltage reaches the thermodynamic sodium precipitation voltage; and after the cell voltage reaches the kinetic sodium precipitation voltage, charging the three-electrode soft-package cell to a full-charge state at a charging rate smaller than 0.1 ℃. The first step, the sodium ion soft package battery core is charged with high multiplying power, the charging multiplying power is 0.5C or above, including 0.5C, 1C, 1.5C, 2C, 3C and 4C, until the battery terminal voltage reaches U 1; secondly, after the battery terminal voltage reaches U 1, the charging multiplying power is adjusted to be between 0.1C and 0.4C, including 0.1C, 0.2C, 0.3C and 0.4C, and the battery terminal voltage reaches U 2; and thirdly, after the battery terminal voltage reaches U 2, charging the battery cell to a full state by using a small multiplying power, wherein the small multiplying power is <0.1C and comprises 0.01C, 0.02C, 0.04C, 0.05C, 0.06C and 0.08C.
According to a formulated step charging strategy, battery cells are charged under different electrolyte injection amounts, and a method for inhibiting sodium precipitation of hard carbon negative electrodes of the sodium ion battery by optimally overlapping the step charging of the electrolyte can be prepared aiming at soft package cells of the sodium ion battery assembled by hard carbon negative electrode materials with different sources.
The method for obtaining the optimization method for inhibiting sodium precipitation of the hard carbon negative electrode by step charging comprises the following steps: and (3) according to a step charging interval divided by a step charging strategy, charging the battery core to a full state by using electrolyte injection amounts with unequal electrolyte injection amounts, disassembling the battery core after charging, and selecting an optimization mode for inhibiting sodium precipitation of the hard carbon negative electrode by step charging according to the sodium precipitation degree of the hard carbon negative electrode.
In the process of filling the battery cell to a full state, the normal electrolyte injection amount is the electrolyte injection amount when the capacity of the three-electrode soft package battery cell is 1Ah, and the unequal electrolyte injection amount is between 1.1 and 2 times of the normal electrolyte injection amount. The different electrolyte injection amounts include: the normal electrolyte injection amount, namely the sodium ion soft package battery core capacity of 1Ah, is 4g, and is defined as normal electrolyte injection amount E 0;0.5E0 and half of the normal electrolyte injection amount; 1.5E 0, 1.5 times the normal injection volume; other liquid injection amounts include 1.1E 0、1.2E0、1.4E0、1.6E0、1.8E0 and 2E 0.
In summary, the method monitors the changes of the hard carbon negative electrode potential and the battery terminal voltage in the charging process in situ by means of the three-electrode soft-package battery core, and provides accurate and reliable basis for dividing the step charging interval; and through electrolyte optimization, stacked ladder charging, the risk of sodium precipitation of different hard carbon cathodes is further reduced. By making a ladder charging strategy: charging the three-electrode soft package battery core with a charging rate of not less than 0.5 ℃ until the battery core voltage reaches the thermodynamic sodium precipitation voltage; after the cell voltage reaches the thermodynamic sodium precipitation voltage, adjusting the charging multiplying power to be within the range of 0.1-0.4C, and recharging until the cell voltage reaches the thermodynamic sodium precipitation voltage; and after the cell voltage reaches the kinetic sodium precipitation voltage, charging the three-electrode soft-package cell to a full-charge state at a charging rate smaller than 0.1 ℃. The impedance of the carbon negative electrode changes with the charge state, and thus the polarization degree of the carbon negative electrode changes. The polarization of the hard carbon cathode is smaller in the low-charge state, and the potential of the hard carbon cathode is more in positive bias sodium isolation potential; the polarization of the hard carbon cathode is larger under the high charge state, and the potential of the hard carbon cathode is closer to the sodium precipitation potential. Therefore, the phenomenon of aggravation of polarization degree can be relieved by charging according to different charge states of the hard carbon negative electrode with proper charging multiplying power, and the early occurrence of sodium precipitation can be effectively restrained.
The invention relates to a method for inhibiting sodium precipitation of a hard carbon negative electrode of a sodium ion battery by electrolyte optimization and superposition step charging, which comprises the following steps: manufacturing a reference electrode or a quasi-reference electrode; implanting a reference electrode or a quasi-reference electrode to construct a three-electrode sodium ion soft-package cell; acquiring a three-electrode soft-package full-battery charging curve, a positive electrode sodium removing curve and a hard carbon negative electrode sodium embedding curve; determination of thermodynamic sodium precipitation terminal voltage: obtaining full cell terminal voltage corresponding to the negative electrode potential of 0V (vs. Na+/Na) or-2V (vs. Pt) through a negative electrode sodium embedding curve, and defining the full cell terminal voltage as thermodynamic sodium precipitation voltage U 1; the determination of the kinetic sodium precipitation terminal voltage is carried out according to the fact that the battery cells charged to different charge states are disassembled, the full battery terminal voltage corresponding to the hard carbon negative electrode when sodium precipitation occurs is obtained, and the full battery terminal voltage is defined as the kinetic sodium precipitation voltage U 2; taking U 1 and U 2 as division basis of step charging intervals, and formulating a step charging strategy of the full battery; s2, charging the battery cell to a full state under different electrolyte addition amounts by using the step charging strategy, and preparing a method for inhibiting sodium precipitation of the hard carbon negative electrode by optimally overlapping the step charging with the electrolyte according to the sodium precipitation degree of the hard carbon negative electrode.
The method is mainly applicable to three-electrode sodium ion soft-package battery cells, sodium ion cylindrical battery cells, sodium ion square shell battery cells and other battery cells.
The above description is only of the preferred embodiments of the present application and is not intended to limit the present application, but various modifications and variations can be made to the present application by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application, that is, the specific embodiments described herein are only illustrative to the spirit of the present application. Those skilled in the art may make various modifications or additions to the described embodiments or substitutions thereof without departing from the spirit of the application or exceeding the scope of the application as defined in the accompanying claims.
Although terms of a step charge strategy, a step charge interval, a normal electrolyte injection amount, etc. are used more herein, the possibility of using other terms is not excluded. These terms are used merely for convenience in describing and explaining the nature of the application; they are to be interpreted as any additional limitation that is not inconsistent with the spirit of the present application.
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