Activation method of sodium-based silicate material as positive electrode of lithium-free lithium-ion battery and its application in lithium-ion battery

Abstract

A method for activating a sodium-based silicate material as a positive electrode for a lithium-ion battery without a lithium source and its application in a lithium-ion battery. The present invention belongs to the field of electrochemistry. The present invention solves the problem in the prior art that sodium-containing electrode materials are directly used as positive electrodes for lithium-ion batteries, resulting in disordered charging curves, poor capacity performance, and the like, which make them unusable. The activation method of the present invention allows sodium-based silicate materials to be used as positive electrodes for lithium-ion batteries without a lithium source. The present invention de-sodiumates and activates sodium-based silicate materials by repeated step-by-step charging combined with cyclic voltammetry technology, thereby overcoming the problems of disordered charging curves and poor capacity performance of sodium-based silicate materials as positive electrodes for lithium-ion batteries without a lithium source, and enabling sodium-based silicate materials to replace lithium source materials as new positive electrode materials for lithium-ion batteries without a lithium source, thereby effectively reducing costs and environmental pollution.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemistry, and in particular relates to an activation method for a sodium-based silicate material as a positive electrode of a lithium-source-free lithium-ion battery and an application of the material in the lithium-ion battery. Background Art

[0002] Secondary batteries, which activate chemical reactions in active materials through charging, can be used repeatedly and are therefore considered an environmentally friendly energy source. Among them, lithium-ion batteries, with their high energy density, long service life, and energy-saving and environmentally friendly features, are widely favored. Positive electrode materials are one of the key materials in lithium-ion batteries. With the demand for increased battery specific capacity, there has been a gradual transition from the initial ternary materials to materials such as high-nickel. While high-nickel materials have high specific capacity, their safety and stability are still unsatisfactory. Therefore, positive electrode materials with high specific energy density, long cycle life, and high voltage will gradually become the focus of research.

[0003] Polyanionic compounds offer a wide variety of materials, diverse structures, adjustable operating voltages, and excellent cycling stability, making them promising cathode materials for the development of low-cost, environmentally friendly secondary batteries. Among these, iron-based silicate cathodes (A2FeSiO4, where A=Li or Na) possess a dual lithium / sodium structure and a multi-electron reaction system constructed with variable-valence transition metals. With theoretical capacities as high as 272-330 mAh / g, they hold the greatest potential for increasing the energy density of energy storage devices. Lithium-containing materials in lithium-ion batteries primarily come from the cathode and electrolyte, driving a growing demand for lithium resources and increasing the production costs of lithium-ion batteries. However, lithium resources are unevenly distributed in the Earth's crust and are limited in reserves, with 70% of the world's lithium being found in South America. Sodium-containing electrodes, similar to lithium-ion batteries, operate by intercalation and deintercalation. Using sodium-containing electrode materials as cathodes for lithium-free lithium-ion secondary batteries could significantly alleviate the need for lithium. Sodium resources are abundant and widely distributed in the Earth's crust, unrestricted by resource reserves and geographical distribution, resulting in low costs and minimal environmental pollution. However, sodium-containing electrode materials cannot be directly used as the positive electrode of lithium-ion batteries due to problems such as disordered charging curves and poor capacity performance. Therefore, developing an activation method that allows sodium-containing electrode materials to be directly used as the positive electrode of lithium-ion batteries is of great significance to economic development, scientific progress and cost savings. Summary of the Invention

[0004] The present invention aims to address the problem of sodium-containing electrode materials being unable to be used directly as positive electrodes in lithium-ion batteries due to irregular charging curves and poor capacity performance. The present invention provides a method for activating sodium-based silicate materials for use as positive electrode materials in lithium-free lithium-ion batteries.

[0005] The technical solutions of the present invention are as follows:

[0006] One of the purposes of the present invention is to provide a method for activating a sodium-based silicate material as a positive electrode of a lithium-ion battery without a lithium source, wherein the specific activation steps are as follows:

[0007] S1: Mix the sodium silicate material, conductive agent and binder evenly, add N-methylpyrrolidone, stir thoroughly to form a slurry, and evenly coat it on aluminum foil. After drying, use it as the positive electrode and the metal lithium sheet as the negative electrode to assemble into a button battery;

[0008] S2: Charge with current I1, voltage range V1-V2, set x step voltages between V1-V2, constant voltage time for each step voltage is T1, then discharge with current I1, repeat n1 times;

[0009] S3: Cyclic voltammetry is applied to the battery after S2 in an electrochemical workstation. Starting from the open circuit voltage, a scan rate of γ1 is set, and the voltage range of V3-V4 is scanned forward n2 times to the cut-off voltage V4.

[0010] It is further defined that the general structural formula of the sodium-based silicate material in S1 is Na2MSiO4, wherein M is at least one of Fe, Mn, Al, Co, Ni, Ti, Cu, Mg or Zn.

[0011] It is further defined that the mass ratio of the sodium-based silicate material, the conductive agent and the binder in S1 is 5-20:1-2:1.

[0012] It is further defined that in S2, 0.2C≤I1≤2C, 1.5V≤V1<V2≤5.0V.

[0013] It is further defined that T1 in S2 is 15-60 min.

[0014] It is further limited that in S2, 1≤n1≤3, 2≤x≤4.

[0015] Further defined, in S3, 0.1 mV / s ≤ γ1 ≤ 5 mV / s, 1.5 V ≤ V3 ≤ 2.0 V, 4.0 V ≤ V4 ≤ 4.8 V. Further defined, in S3, 1 ≤ n2 ≤ 5.

[0016] The second object of the present invention is to provide a method for activating the above-mentioned sodium-based silicate material as a positive electrode of a lithium-free lithium-ion battery to prepare a positive electrode material for a lithium-free lithium-ion battery.

[0017] A third object of the present invention is to provide an application of the above-mentioned lithium-source-free lithium-ion battery positive electrode material in a lithium-source-free lithium-ion battery.

[0018] Compared with the prior art, the specific advantages of the present invention are as follows:

[0019] (1) The sodium-based silicate material selected in the present invention is a polyanion compound with a two-electron reaction, which has a high theoretical capacity and is cheap and safe. The activation method of the sodium-based silicate material of the present invention is the first proposed activation method based on a lithium-free intercalation-extraction positive electrode material. The activation method of the present invention can effectively improve the capacity and cycle performance, and the activation method of the present invention can make the sodium-based silicate material exhibit electrochemical properties equivalent to those of lithium-based silicates.

[0020] (2) The sodium-based silicate material activation method of the present invention can enable the sodium-based silicate material without lithium source to overcome the problems of disordered charging curve and poor capacity performance, greatly saving the use of positive lithium source in lithium-free lithium-ion batteries, effectively reducing costs, reducing resource waste, and achieving green environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a typical step-by-step constant voltage charge and discharge curve;

[0022] Figure 2 is a typical cyclic voltammetry step curve;

[0023] Figure 3 This is a 100-cycle charge-discharge curve of a lithium-ion battery without a lithium source after activation of the sodium-based silicate material in Example 2;

[0024] Figure 4 This is a 100-cycle charge-discharge curve of a lithium-ion battery without a lithium source after activation of the sodium-based silicate material in Example 4;

[0025] Figure 5 The first two charge and discharge curves of the lithium-ion battery without lithium source made of unactivated sodium-based silicate material in Comparative Example 1;

[0026] Figure 6 This is a 100-cycle charge-discharge curve of the sodium-based silicate material lithium-ion battery without lithium source that was only subjected to cyclic voltammetry treatment in Comparative Example 3. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0028] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods, and instruments used are conventional in the art and can be obtained commercially by those skilled in the art unless otherwise specified.

[0029] Example 1:

[0030] S1: Mix 0.96g Na2FeSiO4, 0.12g acetylene black (a conductive agent), and 0.12g polyvinylidene fluoride (a binder), add 10mL N-methylpyrrolidone, and stir thoroughly to form a uniform slurry. Then, use a spatula to evenly coat the slurry on a clean aluminum foil and vacuum dry it at 110°C for 24h to prepare an electrode sheet with a diameter of 16mm as the positive electrode. Finally, assemble the slurry with the negative electrode metal lithium sheet in a glove box to form a button battery.

[0031] S2: Charge the battery in S1 at 0.3C current with a charging voltage range of 1.5-4.6V. Set three gradient voltages of 4.2V, 4.4V, and 4.6V for 30min, 30min, and 15min, respectively. Then discharge the battery at 0.3C current to 1.5V, repeating this cycle three times.

[0032] S3: Cyclic voltammetry (CV) was performed on the button cell of S2 in an electrochemical workstation. The open circuit voltage was used as the starting point, and the scan rate was set to 0.5 mV / s. The voltage range was 1.5-4.6 V, and the forward scan was performed three times to a cutoff voltage of 4.6 V.

[0033] The electrochemical performance test was carried out, and the test parameters and results are shown in Table 1.

[0034] Example 2:

[0035] S1 is the same as Example 1;

[0036] S2: Charge the battery in S1 at 0.3C current with a charging voltage range of 1.5-4.6V. Set three gradient voltages of 4.0V, 4.2V, and 4.4V with constant voltage durations of 30min, 30min, and 60min, respectively. After charging to a cutoff voltage of 4.6V, discharge at 0.3C current to 1.5V, repeating this cycle three times.

[0037] S3: Cyclic voltammetry was performed on the battery of S2 in an electrochemical workstation. The open circuit voltage was used as the starting point, and the scan rate was set to 0.2 mV / s. The voltage range was 1.5-4.6 V, and the forward scan was performed once to the cutoff voltage of 4.6 V.

[0038] The electrochemical performance test was carried out, and the test parameters and results are shown in Table 1.

[0039] Example 3:

[0040] S1 is the same as Example 1;

[0041] S2: Charge the battery in S1 at 0.3C current with a charging voltage range of 1.5-4.6V. Set four gradient voltages of 4.0V, 4.2V, 4.4V and 4.6V. The constant voltage durations are 15min, 15min, 30min and 15min respectively. After charging to a cut-off voltage of 4.6V, discharge at 0.3C current to 1.5V, repeating once.

[0042] S3: Cyclic voltammetry was performed on the battery of S2 in an electrochemical workstation. The open circuit voltage was used as the starting point, and a scan rate of 0.5 mV / s was set. The voltage range of 1.5-4.6 V was scanned in the forward direction twice to a cutoff voltage of 4.6 V.

[0043] The electrochemical performance test was carried out, and the test parameters and results are shown in Table 1.

[0044] Example 4:

[0045] S1 is the same as Example 1;

[0046] S2: Charge the battery in S1 at 1.0C current with a charging voltage range of 1.5-4.6V. Set three gradient voltages of 4.2V, 4.4V, and 4.6V for 30min, 15min, and 30min, respectively. Then discharge it at 0.3C current to 1.5V, repeating this process three times.

[0047] S3: Cyclic voltammetry was performed on the battery of S2 in an electrochemical workstation. The open circuit voltage was used as the starting point, and the scan rate was set to 1.0 mV / s. The voltage range was 1.5-4.6 V, and the forward scan was performed three times to a cutoff voltage of 4.6 V.

[0048] The electrochemical performance test was carried out, and the test parameters and results are shown in Table 1.

[0049] Comparative Example 1:

[0050] S1 is the same as in Example 1, and S2 and S3 are omitted. The activation experiment is not performed. The test conditions are the same as in Example 4. The test parameters and results are detailed in Table 1.

[0051] Comparative Example 2:

[0052] S1 is the same as in Example 1, and S2 and S3 are omitted. No activation experiment is performed. The test conditions are the same as in Example 1. The test parameters and results are detailed in Table 1.

[0053] Comparative Example 3:

[0054] S1 is the same as Example 1;

[0055] S2: Cyclic voltammetry was performed on the button cell of S1 in an electrochemical workstation. The open circuit voltage was used as the starting point, and the scan rate was set to 1.0 mV / s. The voltage range was 1.5-4.6 V, and the forward scan was performed three times to a cutoff voltage of 4.6 V.

[0056] S3 was omitted and the electrochemical performance test was carried out directly. The test conditions were the same as those in Example 1. The test parameters and results are detailed in Table 1.

[0057] Comparative Example 4:

[0058] S1 is the same as Example 1, omitting S2 and directly proceeding to S3: charging the button battery of S1 at a current of 0.3C to a cut-off voltage of 4.6V, maintaining a constant voltage for 60 minutes, and then discharging at a current of 0.3C, repeating this process three times.

[0059] The test conditions are the same as those in Example 1. The test parameters and results are detailed in Table 1.

[0060] Electrochemical performance test:

[0061] Electrochemical performance tests were conducted on Examples 1-4 and Comparative Examples 1-4. Specific test methods: voltage range 1.5-4.6 V, charge and discharge current 0.3 C, cycle test 100 times, test results are detailed in Table 1.

[0062] Table 1: Electrochemical performance test table of Examples 1-4 and Comparative Examples 1-4

[0063]

[0064] As can be seen from Table 1, Examples 1-4 all exhibited an initial discharge capacity of 108-131 mAh / g. After 100 cycles, the discharge capacity remained above 97 mAh / g, and the capacity retention rate was above 84%, showing performance equivalent to that of lithium-based silicate positive electrode materials. Figure 3 This is a 100-cycle charge-discharge curve of a lithium-ion battery without a lithium source after activation of the sodium-based silicate material of Example 2. Figure 4 The charge and discharge curves of the lithium-ion battery without lithium source after activation of the sodium-based silicate material in Example 4 are shown in FIG. Figure 3 and Figure 4 It can be seen that the charge and discharge curves of Example 2 and Example 4 are regular, the cycles are normal, and there is no disorder.

[0065] Figure 5 The first two charge and discharge curves of the lithium-ion battery without lithium source and the unactivated sodium-based silicate material in Comparative Example 1 are shown. Figure 5 It can be seen that in Comparative Example 1, which was not activated according to the present invention, the curves were disordered during the initial two charging processes and normal cycling could not be achieved. This was related to the inability of sodium ions in the active material to be released smoothly.

[0066] Figure 6 This is a 100-cycle charge-discharge curve of a lithium-ion battery made of sodium silicate material and without lithium source, which is processed only by cyclic voltammetry in Comparative Example 3. Figure 6 It can be seen that the coulombic efficiency of comparative example 3 is high, but the capacity attenuation is serious. After 100 charge and discharge cycles, the discharge capacity is only 43mAh / g. This result indicates that after cyclic voltammetry treatment, a phase interface passivation film with a certain stability is formed on the surface of the material, but the sodium ion extraction efficiency in the bulk phase is poor, which reduces the capacity of the material.

[0067] Comparative Example 4 is a sample that has only undergone constant voltage charging. Compared with the example that has undergone step charge and discharge and complete cyclic voltammetry activation, the charge and discharge specific capacity is lower and the capacity decay is faster. Compared with Example 1 that has undergone step charge and discharge and complete cyclic voltammetry activation, the discharge capacity is 30-70 mAh / g lower, which is related to the instability of the interfacial SEI film caused by the lack of the cyclic voltammetry step.

[0068] In summary, the activation method of the present invention can fully remove sodium ions from sodium-based silicate, which helps to form a stable and high-quality SEI film, so that the sodium-based silicate material can be used as the positive electrode of a lithium-free lithium-ion battery.

[0069] The foregoing are merely preferred embodiments of the present invention. These embodiments are all different implementations based on the overall concept of the present invention. The scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for activating a sodium-based silicate material as a positive electrode of a lithium-free lithium-ion battery, characterized in that: The specific activation steps are: S1: Mix a sodium-based silicate material, a conductive agent, and a binder, add N-methylpyrrolidone, stir thoroughly to form a slurry, and evenly coat it on an aluminum foil. After drying, use it as the positive electrode and a metal lithium sheet as the negative electrode to assemble into a button battery; the general structural formula of the sodium-based silicate material is Na2MSiO4, wherein M is at least one of Fe, Mn, Al, Co, Ni, Ti, Cu, Mg, or Zn; S2: Charge with current I1, voltage range V1-V2, set x step voltages between V1-V2, constant voltage time for each step voltage is T1, then discharge with current I1, back and forth n1 times; 0.2C≤I1≤2C, 1.5V≤V1<V2≤5.0V; T1 is 15-60min; 1≤n1≤3, 2≤x≤4; S3: Cyclic voltammetry is applied to the battery after S2 in an electrochemical workstation. Starting from the open circuit voltage, the scan rate is set to γ1. The voltage range of V3-V4 is scanned in the forward direction for n2 times until the cut-off voltage V 4； 0.1mV / s≤γ1≤5mV / s, 1.5V≤V3≤2.0V, 4.0V≤V4≤4.8V; 1≤n2≤5.

2. The method according to claim 1, characterized in that The mass ratio of the sodium-based silicate material, the conductive agent and the binder in S1 is 5-20:1-2:

1.

3. A lithium-source-free lithium-ion battery cathode material, characterized in that: The sodium-based silicate material according to claim 1 or 2 is prepared by an activation method for a lithium-free lithium-ion battery positive electrode.

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