Sodium ion battery and activation method thereof

Abstract

The invention discloses a sodium ion battery and an activation method thereof, the activation method comprises the following steps: a first electrolyte with a concentration of 2-5 mol / L is injected into an assembled cell for pre-activation, a negative electrode material of the cell comprises carbon-coated titanium-based phosphate, the chemical formula of the carbon-coated titanium-based phosphate is K < 1-x > NaxTiOPO4 (at) C, and x is greater than or equal to 0 and less than 0.7; and the first electrolyte is pumped out, and a second electrolyte with the concentration being 1-2 mol / L is injected for activation. Pre-activation is carried out by adopting a strategy of high-concentration electrolyte, wide-range activation voltage and low-rate charging and discharging, rapid exchange of Na-K ions is completed, so that the battery reaches a stable state in a shorter time, the activation time is greatly shortened, meanwhile, the problems of low first efficiency and the like caused by exchange of the Na-K ions during normal activation are avoided, and the service life of the battery is prolonged. And the initial efficiency in the activation stage reaches 95% or above, so that the stability and reliability of the battery in subsequent use are ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a sodium ion battery and an activation method thereof. Background Art

[0002] Sodium-ion batteries have become a promising research direction in the field of energy storage due to their abundant sodium resources and relatively low cost. However, there are still many challenges in the practical application of sodium-ion batteries.

[0003] Sodium titanium phosphate is commonly used as the negative electrode material for sodium ion batteries. The high potential of sodium titanium phosphate comes from the fact that in this crystal structure, only Ti-OP bonds exist. 3- Polyanion to Ti 4+ It has a strong inductive effect, making Ti 4+ To Ti 3+ The electrochemical redox potential corresponding to the valence change is 2.1 V (vs Na / Na + For the titanium phosphate compound ATiOPO4, since the covalency of the titanium-oxygen-titanium bond is weaker than that of the oxygen-phosphorus bond, the redox potential can be significantly reduced to 1.2-1.5 V (vs Na / Na + Among various titanium-based phosphate anode materials, potassium titanyl phosphate (KTiOPO4) has a larger cross-cavity, and KTiOPO4 has the lowest potential of 1.23 V, which has great potential in achieving faster ion dynamics and lower cycle strain in sodium-ion batteries.

[0004] However, when KTiOPO4 carbon composite material is used as the negative electrode material of sodium ion battery, potassium ions will be replaced by sodium ions through ion exchange during the charge and discharge cycle. As the charge and discharge proceed, the specific capacity of the battery first increases and then tends to stabilize, and it can only reach a stable state after more than 400 cycles. This is the K after the sodium ion and potassium ion exchange. 1- x Na x The potential energy of the TiOPO4@C composite in the charged state is lower than that of the reference states KTiOPO4 and NaTiOPO4, which indicates that the exchange of K ions with Na ions is thermodynamically favorable and has the mixed K + / Na +The structure is more stable. In the initial stage of charge and discharge, part of the embedded Na ions undergo K-Na exchange (exchange with K ions in the lattice structure, and Ti does not undergo valence change), and part of them undergo interstitial embedding of Na ions (Ti ions undergo valence change, providing battery capacity). As the Na-K exchange deepens, the proportion of Ti ion valence change gradually increases, so the capacity gradually increases to stability. When it is stable, the Na-K exchange stops, and all reactions are Na ion deintercalation reactions.

[0005] This complex process of ion exchange and embedding requires a long activation time for the battery to reach a stable operating state, which seriously affects the battery's efficiency and practical application. The existing technology is often unsatisfactory in solving this problem, and cannot effectively shorten the activation time and improve the initial efficiency, which greatly limits the widespread application and performance improvement of sodium-ion batteries. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention provides a sodium ion battery and an activation method thereof. Before the normal battery activation step, a high-concentration electrolyte, a wide range of activation voltages, and a low-rate charge-discharge strategy are used for pre-activation to achieve rapid exchange of Na-K ions. Then, the electrolyte is replaced and the battery is normally activated. At this time, the first activation efficiency reaches more than 95%. By setting the pre-activation parameters, the activation time is greatly shortened, the first efficiency is significantly improved, and the stability and reliability of the battery in subsequent use are ensured.

[0007] In order to solve the above technical problems, the present invention provides a method for activating a sodium ion battery, comprising the following steps:

[0008] S1. Injecting a first electrolyte into the assembled battery cell for pre-activation, wherein the concentration C1 of the electrolyte salt in the first electrolyte is 2-5 mol / L;

[0009] The negative electrode material of the battery cell includes a carbon-coated titanium-based phosphate, the chemical formula of which is K 1-x Na x TiOPO4@C, where 0≤x<0.7;

[0010] S2. Draw out the first electrolyte and inject the second electrolyte for activation, wherein the concentration C2 of the electrolyte salt in the second electrolyte is 1-2 mol / L.

[0011] Furthermore, in S1, the pre-activation is specifically: charging to 3.5V at a rate of 0.1-1C, and then discharging to 0V, and the number of pre-activation cycles is 2-20 cycles.

[0012] Furthermore, in S2, the activation is specifically as follows: charging to 3V at a rate of 1-2C, and then discharging to 0.5V, and the number of activation cycles is 2 cycles.

[0013] Furthermore, in S2, the initial efficiency during activation is greater than>95%.

[0014] The present invention sets a pre-activation step before the normal activation step, adopts a high-concentration electrolyte, a wide range of activation voltages, and a low-rate charge-discharge strategy for pre-activation, completes the rapid exchange of Na-K ions, and enables the battery to reach a stable state in a shorter time. At the same time, it avoids the problem of low initial efficiency caused by the exchange of Na-K ions during normal activation. When the electrolyte is replaced for normal activation of the battery, the initial activation efficiency reaches more than 95%. At the same time, K 1-x Na x TiOPO4@C negative electrode material can be doped with sodium salt during the preparation of potassium titanyl phosphate carbon composite material to further reduce Na-K ion exchange. However, the doping ratio of Na ions should not be too high. When x≥0.7, as the proportion of potassium ions decreases, the potassium ions that serve as framework support during the charge and discharge process become less and less, and the sodium ion deintercalation tends to be difficult, which is manifested as a decrease in specific capacity and a decrease in the sodium ion diffusion coefficient. Therefore, the doping of sodium ions is limited to a specific range, and pre-activation is combined to obtain a stable negative electrode material.

[0015] The present invention greatly shortens the activation time and significantly improves the initial efficiency by setting the pre-activation parameters, thereby ensuring the stability and reliability of the battery in subsequent use, and providing strong technical support for the widespread application of sodium ion batteries.

[0016] Further, after S2, the negative electrode material K 1-x Na x The x range of TiOPO4@C is 0.7≤x≤0.85.

[0017] Further, in S1, the battery cell further comprises a positive electrode, and the positive electrode comprises a polyanion material Na 4-a Fe 3-b (PO4)2(P2O7), wherein a=0-1, b=0-1.

[0018] Furthermore, the electrolyte salt of the first electrolyte and the second electrolyte is selected from one or more of sodium hexafluorophosphate, sodium perchlorate, sodium bis(oxalate)borate, sodium bis(salicylate)borate and sodium tetraphenylborate.

[0019] Furthermore, the first electrolyte and the second electrolyte further include an organic solvent, and the organic solvent is selected from one or more of ethyl methyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, dimethyl carbonate and diethylene glycol dimethanol ether.

[0020] Furthermore, the first electrolyte extracted from S2 is supplemented with electrolyte salt to a concentration of C1 and then recycled into S1 as the first electrolyte in S1, thereby realizing the recycling of the electrolyte and saving energy.

[0021] The second aspect of the present invention provides a sodium ion battery prepared by the activation method described in the first aspect.

[0022] Beneficial effects of the present invention:

[0023] The present invention arranges a pre-activation step before a normal activation step, adopts a high-concentration electrolyte, a wide range of activation voltages, and a low-rate charge-discharge strategy for pre-activation, completes the rapid exchange of Na-K ions, enables the battery to reach a stable state in a shorter time, and avoids problems such as low initial efficiency caused by the exchange of Na-K ions during normal activation; when the electrolyte is replaced for normal activation operation of the battery, the initial activation efficiency reaches more than 95%.

[0024] Compared with the traditional activation method, the present invention greatly shortens the activation time and significantly improves the initial efficiency by setting the pre-activation parameters, thus ensuring the stability and reliability of the battery in subsequent use, and providing strong technical support for the widespread application of sodium ion batteries. DETAILED DESCRIPTION

[0025] The technical solution of the present invention will be described clearly and completely below in conjunction with the specific embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] The present invention relates to a method for activating a sodium ion battery, comprising the following steps:

[0027] S1. Inject the assembled battery cell into a first electrolyte for pre-activation, wherein the concentration of electrolyte salt in the first electrolyte is 2-5 mol / L; the negative electrode material of the battery cell includes a carbon-coated titanium-based phosphate, whose chemical formula is K 1- x Na x TiOPO4@C, where 0≤x<0.7;

[0028] Specifically, the pre-activation is specifically: charging to 3.5V at a rate of 0.1-1C, and then discharging to 0V, and the number of pre-activation cycles is 2-20 cycles;

[0029] S2, extracting the first electrolyte and injecting the second electrolyte for activation, wherein the concentration C2 of the electrolyte salt in the second electrolyte is 1-2 mol / L;

[0030] Specifically, the activation is as follows: charging to 3V at a rate of 1-2C, and then discharging to 0.5V, and the number of activation cycles is 2 cycles.

[0031] In this embodiment, a pre-activation step S1 is set before the normal activation step S2, and a high-concentration electrolyte, a wide range of activation voltage, and a low-rate charge-discharge strategy are used for pre-activation to complete the rapid exchange of Na-K ions. 1-x Na x The x range of TiOPO4@C is increased to 0.7≤x≤0.85, so that the battery can reach a stable state in a shorter time, avoiding the problem of low initial efficiency caused by the exchange of Na-K ions during normal activation; when the second electrolyte is replaced for normal activation operation of the battery, the initial activation efficiency reaches more than 95%. 1-x Na x TiOPO4@C negative electrode material pre-dopes sodium into potassium titanyl phosphate carbon composite material to further reduce Na-K ion exchange; by setting pre-activation parameters, the activation time is greatly shortened, the first efficiency is significantly improved, and the stability and reliability of the battery in subsequent use are ensured, providing strong technical support for the widespread application of sodium-ion batteries.

[0032] As an embodiment, the battery cell further comprises a positive electrode, wherein the positive electrode comprises a polyanion material Na 4-a Fe 3-b (PO4)2(P2O7), wherein a=0-1, b=0-1. The electrolyte salt of the first electrolyte and the second electrolyte is selected from one or more of sodium perchlorate, sodium bis(oxalate)borate, sodium bis(salicylate)borate and sodium tetraphenylborate. The first electrolyte and the second electrolyte also include an organic solvent, and the organic solvent is selected from one or more of ethyl methyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, dimethyl carbonate and diethylene glycol dimethanol ether.

[0033] As an implementation mode, the first electrolyte extracted from S2 is supplemented with electrolyte salt to a concentration of C1 and then recycled into S1 as the first electrolyte in S1, thereby realizing the recycling of the electrolyte and saving energy.

[0034] Another embodiment provides a sodium ion battery prepared by the activation method described in the above embodiment.

[0035] Example 1

[0036] This embodiment relates to a method for activating a sodium ion battery, comprising the following steps:

[0037] (1) Preparation of negative electrode active materials: Weigh the corresponding mass of potassium dihydrogen phosphate, anatase phase titanium dioxide and glucose (glucose is carbonized as carbon coating material, and the mass of carbon coating material is 0.8% of the total mass of negative electrode active materials) according to the stoichiometric ratio, add deionized water, solid content is 50%, put into a planetary ball mill, use zirconium oxide beads as grinding media, material-to-ball ratio is 2:1, ball mill at 400 rpm and 80 ° C for 5 h, and use a laser particle size analyzer to test the slurry particle size. diameter until the particle size D50 of the slurry is less than 0.5μm; the slurry is then spray-dried in a centrifugal spray dryer with an inlet air temperature of 200℃ and a rotation speed of 15000rpm to obtain a precursor with a particle size D50 of about 10μm; the precursor is transferred to a tubular furnace in a nitrogen atmosphere, heated to 700℃ at a heating rate of 2℃ / min and kept warm for 5h, and then ground after naturally cooling to room temperature to obtain a sodium ion battery negative electrode material KTiOPO4@C composite material.

[0038] (2) Preparation of battery cells: The positive and negative electrode active materials, conductive carbon black, polyvinylidene fluoride, and N-methyl-2-pyrrolidone were mixed uniformly at a mass ratio of 97:2:1:150 to obtain positive and negative electrode slurries, respectively. The positive electrode active material was sodium iron pyrophosphate Na 3.5 Fe 2.9 (PO4)2(P2O7); the negative electrode active material is the KTiOPO4@C composite material prepared in step (1); the positive and negative electrode slurries are coated on aluminum foil respectively, dried at 120°C, rolled at 4.0MPa, and die-cut into positive electrode sheets with a size of 56mm*43mm and negative electrode sheets with a size of 58mm*45mm; the sheets are stacked in a Z-shape in the order of "positive electrode sheet, diaphragm, negative electrode sheet, diaphragm", with the number of stacked layers being 199 layers of positive electrode sheets and 200 layers of negative electrode sheets, and after making welding ears, the sheets are put into the shell, placed in a vacuum oven with a vacuum degree of -0.095MPa and a temperature of 120°C and baked for 12h to obtain dry cells, and the cells to be activated are assembled.

[0039] (3) Injecting the battery cell to be activated into the first electrolyte for pre-activation, wherein the solvent of the first electrolyte is ethylene carbonate, the electrolyte salt is sodium hexafluorophosphate, the concentration is 3 mol / L, charging to 3.5 V at a rate of 0.2C, discharging to 0 V, and pre-activating for 10 cycles;

[0040] (4) After the first electrolyte is extracted, the second electrolyte is injected for normal activation, wherein the solvent of the second electrolyte is ethylene carbonate, the electrolyte salt is sodium hexafluorophosphate, the concentration is 1 mol / L, and the battery is charged to 3 V at a rate of 1 C, discharged to 0.5 V, and pre-activated for 2 cycles.

[0041] Example 2

[0042] This embodiment relates to a method for activating a sodium ion battery. The difference from Embodiment 1 is that the concentration of the electrolyte salt of the first electrolyte in step (2) is 2 mol / L, and the other steps and parameters remain unchanged.

[0043] Example 3

[0044] This embodiment relates to a method for activating a sodium ion battery. The difference from Embodiment 1 is that the concentration of the electrolyte salt of the first electrolyte in step (2) is 5 mol / L, and the other steps and parameters remain unchanged.

[0045] Example 4

[0046] This embodiment relates to a method for activating a sodium ion battery. The difference from Embodiment 1 is that in step (2), the charging rate is 0.1C, the number of pre-activation cycles is 3, and the other steps and parameters remain unchanged.

[0047] Example 5

[0048] This embodiment relates to a method for activating a sodium ion battery. The difference from Embodiment 1 is that in step (2), the charging rate is 0.5C, the number of pre-activation cycles is 5, and the other steps and parameters remain unchanged.

[0049] Example 6

[0050] This embodiment relates to a method for activating a sodium ion battery. The difference from Embodiment 1 is that in step (2), the charging rate is 1C, the number of pre-activation cycles is 20, and the other steps and parameters remain unchanged.

[0051] Example 7

[0052] This embodiment relates to a method for activating a sodium ion battery. The difference from the embodiment 1 is that in step (1), the negative electrode active material prepared by adding sodium carbonate in a stoichiometric ratio is K 0.9 Na 0.1 TiOPO4@C composite material, and other steps and parameters remained unchanged.

[0053] Example 8

[0054] This embodiment relates to a method for activating a sodium ion battery. The difference from Embodiment 7 is that the negative electrode active material prepared in step (1) is K 0.8 Na 0.2 TiOPO4@C composite material, and other steps and parameters remained unchanged.

[0055] Example 9

[0056] This embodiment relates to a method for activating a sodium ion battery. The difference from Embodiment 7 is that the negative electrode active material prepared in step (1) is K 0.6 Na 0.4TiOPO4@C composite material, and other steps and parameters remained unchanged.

[0057] Comparative Example 1

[0058] This comparative example relates to a method for activating a sodium ion battery, which differs from Example 1 in that the battery is charged to 3 V in step (2), and the other steps and parameters remain unchanged.

[0059] Comparative Example 2

[0060] This comparative example relates to a method for activating a sodium ion battery, which differs from Example 1 in that the concentration of the electrolyte salt of the first electrolyte in step (2) is 1 mol / L, and the other steps and parameters remain unchanged.

[0061] Comparative Example 3

[0062] This comparative example relates to a method for activating a sodium ion battery, which differs from Example 1 in that the concentration of the electrolyte salt of the first electrolyte in step (2) is 6 mol / L, and the other steps and parameters remain unchanged.

[0063] Comparative Example 4

[0064] This comparative example relates to a method for activating a sodium ion battery, which differs from Example 1 in that the charging rate in step (2) is 2C, the number of pre-activation cycles is 30, and the other steps and parameters remain unchanged.

[0065] Comparative Example 5

[0066] This comparative example relates to a method for activating a sodium ion battery, which differs from Example 1 in that the charging rate in step (2) is 0.1C, the number of pre-activation cycles is 1, and the other steps and parameters remain unchanged.

[0067] Test Case

[0068] The sodium ion batteries activated in Examples 1-9 and Comparative Examples 1-5 were placed on a battery cycle test device with a discharge voltage range of 0.5V-3V. The sodium ion batteries were subjected to a 5C charge and 5C discharge cycle test at room temperature, and the number of cycles at which the capacity tended to be stable was recorded. At the same time, the capacity Qstable when the capacity was stable and the capacity Q3000 at the 3000th cycle were recorded. The capacity retention rate of each battery after 3000 cycles was calculated as (Q3000 cycles / Qstable)×100%. The first effect in the activation stage = the ratio of the activation capacity in step (3) / the design capacity (10Ah). The performance test results of the batteries in Examples 1-9 and Comparative Examples 1-5 are shown in Table 1.

[0069]

[0070]

[0071] It can be seen from Table 1 that the battery cycle stability number of obtained under the activation conditions of Examples 1-6 is small, because the Na-K exchange is completed in the pre-activation stage, and the number of stable cycles is the change of voltage adjustment, which is stable within 5 cycles, and the first efficiency in the activation stage and the 3000-cycle capacity retention rate are both at a high level, and the battery performance is stable.

[0072] From the comparison between Example 1 and Examples 7-9, it can be seen that Examples 7-9 use different negative electrode active materials. It can be seen that with the increase of the proportion of Na ions in the negative electrode active material, the first efficiency in the activation stage is slightly improved. This is mainly because the Na ions contained in the material itself can further shorten the degree of K-Na exchange and improve the first efficiency in the activation stage and the cycle stability.

[0073] From the comparison between Example 1 and Comparative Example 1, it can be seen that the pre-activation voltage range in Comparative Example 1 is narrow, resulting in incomplete Na-K exchange, which leads to a decrease in the first coulombic efficiency and an extension of the cycle stability number during the later normal activation. However, in Example 1, there is no capacity growth process after activation, and the activation number is the capacity stability number.

[0074] From the comparison between Example 1 and Comparative Examples 2-3, it can be seen that in Comparative Example 2, the electrolyte concentration is 1 mol / L. Since complete Na-K exchange cannot be achieved in the pre-activation stage, the first effect in the activation stage is reduced, and the number of cycle stability circles is large; in Comparative Example 3, the electrolyte concentration is 6 mol / L. Due to the 0.2C low rate charge and discharge, the high voltage stage time is longer. In the pre-activation stage, K ions may be completely exchanged by Na ions, resulting in changes in the lattice structure, and the long-term cycle stability in the later stage is very poor.

[0075] From the comparison between Example 1 and Comparative Examples 4-5, it can be seen that in Comparative Example 4, 30 cycles of pre-activation at a 2C rate, the first efficiency in the activation stage is only 84.9%, and the number of cycle stability cycles is large. This is because under the high-rate charging state, the high voltage time at the end of charging is short, which is not enough to provide time for Na-K exchange; in Comparative Example 5, 1 cycle of pre-activation at a 0.1C rate is not enough to complete the Na-K exchange, the first efficiency in the activation stage is low, and the number of cycle stability cycles is large.

[0076] The present invention has been described in detail above in conjunction with specific implementations and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached claims.

Claims

1. A method for activating a sodium ion battery, characterized in that: The steps include: S1. Injecting a first electrolyte into the assembled battery cell for pre-activation, wherein the concentration C1 of the electrolyte salt in the first electrolyte is 2-5 mol / L; The negative electrode material of the battery cell includes a carbon-coated titanium-based phosphate, the chemical formula of which is K 1-x Na x TiOPO4@C, where 0≤x<0.7; S2. Draw out the first electrolyte and inject the second electrolyte for activation, wherein the concentration C2 of the electrolyte salt in the second electrolyte is 1-2 mol / L.

2. The method for activating a sodium ion battery according to claim 1, wherein: In S1, the pre-activation is specifically: charging to 3.5V at a rate of 0.1-1C, and then discharging to 0V, and the number of pre-activation cycles is 2-20 cycles.

3. The method for activating a sodium ion battery according to claim 1, wherein: In S2, the activation is specifically as follows: charging to 3V at a rate of 1-2C, and then discharging to 0.5V, and the number of activation cycles is 2 cycles.

4. The method for activating a sodium ion battery according to claim 1, wherein: In S2, the initial efficiency during activation is >95%.

5. The method for activating a sodium ion battery according to claim 1, wherein: After S2, the negative electrode material K 1- x Na x The x range of TiOPO4@C is 0.7≤x≤0.

85.

6. The method for activating a sodium ion battery according to claim 1, wherein: In S1, the battery cell further comprises a positive electrode, wherein the positive electrode comprises a polyanion material Na 4-a Fe 3-b (PO4)2(P2O7), wherein a=0-1, b=0-1.

7. The method for activating a sodium ion battery according to claim 1, wherein: The electrolyte salt of the first electrolyte and the second electrolyte is selected from one or more of sodium hexafluorophosphate, sodium perchlorate, sodium bis(oxalate)borate, sodium bis(salicylate)borate and sodium tetraphenylborate.

8. The method for activating a sodium ion battery according to claim 1, wherein: The first electrolyte and the second electrolyte further include an organic solvent, and the organic solvent is selected from one or more of ethyl methyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, dimethyl carbonate and diethylene glycol dimethanol ether.

9. The method for activating a sodium ion battery according to claim 1, wherein: The first electrolyte extracted from S2 is supplemented with electrolyte salt to a concentration of C1 and then reused in S1.

10. A sodium ion battery prepared by the activation method according to any one of claims 1 to 9.

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