Composite secondary battery system

Abstract

The invention discloses a composite secondary battery system which comprises a positive electrode material, a negative electrode material and an electrolyte, the chemical formula of the positive electrode material is NaxK (1-x) CryTM (1-y) O2, and x ranges from 0.25 to 0.75; y ranges from 0.9 to 1; tM is a transition metal element, the transition metal TM is used as a doping ion, and the proportion is not more than 10%. The negative electrode material comprises a carbon material, an alloy material or a combination of the carbon material and the alloy material; the electrolyte is an electrolyte organic solution containing sodium ions and potassium ions at the same time; a charge-discharge potential window is 1.5-3.8 V, and the potential window not only can ensure the stability of the positive electrode structure, but also can ensure that all sodium ions in the positive electrode material participate in deintercalation and potassium ions participate in deintercalation as much as possible, so that the energy release of a composite secondary battery system is fully realized; the composite secondary battery system has the characteristics of good cycling stability, high energy density and wide electrochemical window.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and in particular to a composite secondary battery system. Background Art

[0002] Power modules based on lithium-ion batteries have been the main driving force behind the explosive growth of portable electronic devices and the re-emergence of electric vehicles in the past decade. However, as the demand for lithium-ion batteries increases, the shortage of lithium resources and the rising prices of lithium batteries have become a problem, which also restricts the further large-scale application of energy storage devices. In contrast, the abundance of sodium and potassium in the earth's crust is the sixth and seventh, respectively, far higher than that of lithium. Both are abundant and cheap. From a resource perspective, sodium-ion batteries and potassium-ion batteries are both ideal battery systems. The standard electrode potentials of lithium, sodium and potassium are -3.04 V, -2.71 V and -2.92 V, respectively. Due to the high standard electrode potential of sodium, the energy density of sodium-ion batteries is low. Considering the abundance of lithium, sodium and potassium in the earth's crust and their standard electrode potentials, sodium-potassium dual-ion batteries are one of the alternatives for large-scale application of battery systems.

[0003] In recent years, sodium ion batteries and potassium ion batteries have developed rapidly. + The standard electrode potential is -2.71 V, which is significantly higher than Li / Li + At standard electrode potential, the energy density of sodium-ion batteries is significantly lower than that of lithium-ion batteries, which restricts their application in electric vehicles, digital 3C and other fields; the potassium-ion battery system has a higher voltage platform, but due to the large size of potassium ions, the structure is prone to collapse when the escape ratio is too high, and deep discharge is impossible, so the discharge specific capacity is relatively low.

[0004] Composite secondary battery system is a new type of energy storage technology, which is mainly divided into anion-cation dual-ion batteries and multiple cation dual-ion batteries. Sodium-potassium dual-ion batteries are one of the typical representatives of composite secondary battery systems. Sodium and potassium elements are abundant in the earth's crust and have low costs. They also have high specific capacity and ideal voltage platforms. In addition, sodium-potassium dual-ion batteries can combine the advantages of sodium-ion batteries and potassium-ion batteries. They are potential substitutes for lithium-ion batteries and are a very promising development direction. However, there are few positive electrode materials suitable for composite secondary battery systems, and they are in the initial stage. Summary of the invention

[0005] The object of the present invention is to provide a composite secondary battery system having the characteristics of good cycle stability, high energy density and wide electrochemical window.

[0006] The present invention can be implemented by the following technical solutions: The present invention discloses a composite secondary battery system, comprising a positive electrode material, a negative electrode material and an electrolyte. The chemical formula of the positive electrode material is Na x K 1-x Cr y TM 1-y O2, wherein: x ranges from 0.25 to 0.75; y ranges from 0.9 to 1; TM is a transition metal element, and the transition metal TM is used as a doping ion, accounting for no more than 10%.

[0007] Furthermore, the negative electrode material is a carbon material and / or an alloy material.

[0008] Furthermore, the electrolyte includes: an electrolyte having both sodium ions and potassium ions and an organic solvent; and the charge and discharge potential window is 1.5 V to 3.8 V. The potential window can not only ensure the stability of the positive electrode structure, but also ensure that all sodium ions in the positive electrode material participate in the insertion and extraction, and potassium ions participate in the insertion and extraction as much as possible, thereby fully realizing the release of energy of the composite secondary battery system.

[0009] Furthermore, the organic solvent includes, but is not limited to, one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene glycol dimethyl ether, vinylene carbonate, acetonitrile, succinonitrile, and isobutyronitrile.

[0010] Furthermore, the sodium-containing electrolyte includes, but is not limited to, one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium bistrifluoromethanesulfonate, sodium difluorooxalatoborate, sodium bisfluorosulfonyl imide and sodium bisoxalatoborate.

[0011] Furthermore, the potassium-containing electrolyte includes, but is not limited to, one or more of potassium hexafluorophosphate, potassium tetrafluoroborate, potassium perchlorate, potassium tetrafluoroborate, potassium bistrifluoromethanesulfonate, potassium difluorooxalatoborate, potassium bisfluorosulfonyl imide and potassium bisoxalatoborate.

[0012] Furthermore, the carbon negative electrode material is hard carbon and / or graphite.

[0013] Furthermore, the positive electrode material and the negative electrode material are formed into positive electrode sheets and negative electrode sheets through manufacturing, and then separated by a separator and wound or stacked.

[0014] Furthermore, the secondary battery is a cylindrical battery or a square battery.

[0015] The composite secondary battery system of the present invention has the following beneficial effects: The composite secondary battery system of the present invention uses Na x K 1-x Cr y TM 1-yO2 layered oxide material is used as the positive electrode. By optimizing the ratio of sodium and potassium ions in the structure and optimizing the doping ratio of transition metal ions, when it is used as the positive electrode material of the composite secondary battery system, the structural limitations of the chromium-based oxide material are eliminated. Under the premise of ensuring cycle stability, the energy density of the dual cation battery system can be maximized; the composite secondary battery system of the present invention effectively expands the structural richness of the negative electrode and can effectively increase the proportion of graphite used in the negative electrode; the composite secondary battery system of the present invention can not only ensure the stability of the positive electrode structure within its charge and discharge potential window, but also ensure that all sodium ions in the positive electrode material participate in the insertion and extraction, and potassium ions participate in the insertion and extraction as much as possible, thereby fully realizing the release of energy of the composite secondary battery system. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the cycle performance test curve of Example 1. DETAILED DESCRIPTION

[0017] In order to enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention is further described in detail below in conjunction with embodiments.

[0018] The present invention discloses a composite secondary battery system, comprising a positive electrode material, a negative electrode material and an electrolyte. The chemical formula of the positive electrode material is Na x K 1-x Cr y TM 1-y O2, wherein: x ranges from 0.25 to 0.75; y ranges from 0.9 to 1; TM is a transition metal element, and the transition metal TM is used as a doping ion, accounting for no more than 10%.

[0019] Furthermore, the negative electrode material is a carbon material and / or an alloy material.

[0020] Furthermore, the electrolyte includes: an electrolyte having both sodium ions and potassium ions and an organic solvent; and a charge and discharge potential window of 1.5 V to 3.8 V.

[0021] Furthermore, the organic solvent includes, but is not limited to, one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene glycol dimethyl ether, vinylene carbonate, acetonitrile, succinonitrile, and isobutyronitrile.

[0022] Furthermore, the sodium-containing electrolyte includes, but is not limited to, one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium bistrifluoromethanesulfonate, sodium difluorooxalatoborate, sodium bisfluorosulfonyl imide and sodium bisoxalatoborate.

[0023] Furthermore, the potassium-containing electrolyte includes, but is not limited to, one or more of potassium hexafluorophosphate, potassium tetrafluoroborate, potassium perchlorate, potassium tetrafluoroborate, potassium bistrifluoromethanesulfonate, potassium difluorooxalatoborate, potassium bisfluorosulfonyl imide and potassium bisoxalatoborate.

[0024] Furthermore, the carbon negative electrode material is hard carbon and / or graphite.

[0025] Furthermore, the positive electrode material and the negative electrode material are formed into positive electrode sheets and negative electrode sheets through manufacturing, and then separated by a separator and wound or stacked.

[0026] Furthermore, the secondary battery is a cylindrical battery or a square battery.

[0027] Example 1 This embodiment relates to a composite secondary battery system, and its preparation method is as follows: 1. Put Na 0.5 K 0.5 CrO2 is used as a positive electrode material, and a positive electrode sheet is prepared using the positive electrode material, PVDF, and conductive carbon in a mass ratio of 8:1:1; 2. Hard carbon is used as the negative electrode material. The negative electrode sheet is prepared with the negative electrode material, CMC and conductive carbon in a mass ratio of 90:5:5 to ensure that the N / P ratio of the positive and negative electrode sheets is 1.2; 3. Use 1 mol / L NaPF6 and 1 mol / L KPF6 EC:DMC (3:7) solution as the electrolyte; 4. Assemble the composite secondary battery in a glove box filled with argon; 5. The operating voltage window of the composite secondary battery system is 1.5 V~3.8 V.

[0028] Example 2 This embodiment relates to a composite secondary battery system, and its preparation method is as follows: 1. Put Na 0.25 K 0.75 CrO2 is used as a positive electrode material, and a positive electrode sheet is prepared using the positive electrode material, PVDF, and conductive carbon in a mass ratio of 8:1:1; 2. Hard carbon is used as the negative electrode material. The negative electrode sheet is prepared with the negative electrode material, CMC and conductive carbon in a mass ratio of 90:5:5 to ensure that the N / P ratio of the positive and negative electrode sheets is 1.2; 3. Use 1 mol / L NaPF6 and 1 mol / L KPF6 EC:DMC (3:7) solution as the electrolyte; 4. Assemble the composite secondary battery in a glove box filled with argon; 5. The operating voltage window of the composite secondary battery system is 1.5 V~3.8 V.

[0029] Example 3 This embodiment relates to a composite secondary battery system, and its preparation method is as follows: 1. Put Na 0.35 K 0.65 CrO2 is used as a positive electrode material, and a positive electrode sheet is prepared using the positive electrode material, PVDF, and conductive carbon in a mass ratio of 8:1:1; 2. Hard carbon: graphite (9:1) is mixed as the negative electrode material. The negative electrode material, CMC, and conductive carbon are used to prepare the negative electrode sheet in a mass ratio of 90:5:5 to ensure that the N / P ratio of the positive and negative electrode sheets is 1.2; 3. Use 1 mol / L NaPF6 and 1 mol / L KPF6 EC:DMC (3:7) solution as the electrolyte; 4. Assemble the composite secondary battery in a glove box filled with argon; 5. The operating voltage window of the composite secondary battery system is 1.5 V~3.8 V.

[0030] Example 4 This embodiment relates to a composite secondary battery system, and its preparation method is as follows: 1. Put Na 0.3 K 0.7 CrO2 is used as a positive electrode material, and a positive electrode sheet is prepared using the positive electrode material, PVDF, and conductive carbon in a mass ratio of 8:1:1; 2. Hard carbon is used as the negative electrode material. The negative electrode sheet is prepared with the negative electrode material, CMC and conductive carbon in a mass ratio of 90:5:5 to ensure that the N / P ratio of the positive and negative electrode sheets is 1.2; 3. Use EC:DMC (3:7) solution of 1mol / L NaClO4 and 1mol / L KPF6 as the electrolyte; 4. Assemble the composite secondary battery in a glove box filled with argon; 5. The operating voltage window of the composite secondary battery system is 1.5 V~3.8 V.

[0031] Example 5 This embodiment relates to a composite secondary battery system, and its preparation method is as follows: 1. Put Na 0.4 K 0.6 Cr 0.99 W 0.01 O2 is used as the positive electrode material, and the positive electrode sheet is prepared by using the positive electrode material, PVDF and conductive carbon in a mass ratio of 8:1:1; 2. Hard carbon is used as the negative electrode material. The negative electrode sheet is prepared with the negative electrode material, CMC and conductive carbon in a mass ratio of 90:5:5 to ensure that the N / P ratio of the positive and negative electrode sheets is 1.2; 3. Use EC:EMC:FEC (3:5:2) solution of 1mol / L NaPF6 and 1mol / L KPF6 as the electrolyte; 4. Assemble the composite secondary battery in a glove box filled with argon; 5. The operating voltage window of the composite secondary battery system is 1.5 V~3.8 V.

[0032] Example 6 This embodiment relates to a composite secondary battery system, and its preparation method is as follows: 1. Put Na 0.55 K 0.45 CrO2 is used as a positive electrode material, and a positive electrode sheet is prepared using the positive electrode material, PVDF, and conductive carbon in a mass ratio of 8:1:1; 2. Hard carbon: graphite: tin (6:3:1) is mixed as the negative electrode material. The negative electrode material, CMC, and conductive carbon are used to prepare the negative electrode sheet in a mass ratio of 90:5:5 to ensure that the N / P ratio of the positive and negative electrode sheets is 1.2; 3. Use 1 mol / L NaPF6 and 1 mol / L KPF6 EC:DMC (3:7) solution as the electrolyte; 4. Assemble the composite secondary battery in a glove box filled with argon; 5. The operating voltage window of the composite secondary battery system is 1.5 V~3.8 V.

[0033] Example 7 This embodiment relates to a composite secondary battery system, and its preparation method is as follows: 1. Put Na 0.4 K 0.6 CrO2 is used as a positive electrode material, and a positive electrode sheet is prepared using the positive electrode material, PVDF, and conductive carbon in a mass ratio of 8:1:1; 2. Hard carbon is used as the negative electrode material. The negative electrode sheet is prepared with the negative electrode material, CMC and conductive carbon in a mass ratio of 90:5:5 to ensure that the N / P ratio of the positive and negative electrode sheets is 1.2; 3. Use PC:DMC (3:7) solution of 1 mol / L NaClO4 and 1 mol / L KClO4 as the electrolyte; 4. Assemble the composite secondary battery in a glove box filled with argon; 5. The operating voltage window of the composite secondary battery system is 1.5 V~3.8 V.

[0034] Example 8 This embodiment relates to a composite secondary battery system, and its preparation method is as follows: 1. Put Na 0.3 K 0.7 Cr0.97 Mn 0.03 O2 is used as the positive electrode material, and the positive electrode sheet is prepared by using the positive electrode material, PVDF and conductive carbon in a mass ratio of 8:1:1; 2. Hard carbon is used as the negative electrode material. The negative electrode sheet is prepared with the negative electrode material, CMC and conductive carbon in a mass ratio of 90:5:5 to ensure that the N / P ratio of the positive and negative electrode sheets is 1.2; 3. Use 2mol / L NaPF6 and 1mol / L KPF6 EC:DMC (2:8) solution as the electrolyte; 4. Assemble the composite secondary battery in a glove box filled with argon; 5. The operating voltage window of the composite secondary battery system is 1.5 V~3.8 V.

[0035] Example 9 This embodiment relates to a composite secondary battery system, and its preparation method is as follows: 1. Put Na 0.65 K 0.35 CrO2 is used as a positive electrode material, and a positive electrode sheet is prepared using the positive electrode material, PVDF, and conductive carbon in a mass ratio of 8:1:1; 2. Hard carbon: graphite (7:3) is mixed as the negative electrode material. The negative electrode material, CMC, and conductive carbon are used to prepare the negative electrode sheet in a mass ratio of 90:5:5 to ensure that the N / P ratio of the positive and negative electrode sheets is 1.2; 3. Use EC:DME:AN (3:3:4) solution of 1mol / L NaPF6 and 1mol / L KPF6 as the electrolyte; 4. Assemble the composite secondary battery in a glove box filled with argon; 5. The operating voltage window of the composite secondary battery system is 1.5 V~3.8 V.

[0036] Example 10 This embodiment relates to a composite secondary battery system, and its preparation method is as follows: 1. Put Na 0.45 K 0.55 Cr 0.95 Ti 0.05 O2 is used as the positive electrode material, and the positive electrode sheet is prepared by using the positive electrode material, PVDF and conductive carbon in a mass ratio of 8:1:1; 2. Hard carbon is used as the negative electrode material. The negative electrode sheet is prepared with the negative electrode material, CMC and conductive carbon in a mass ratio of 90:5:5 to ensure that the N / P ratio of the positive and negative electrode sheets is 1.2; 3. Use 1 mol / L NaDFOB and 2 mol / L KPF6 EC:DMC (3:7) solution as the electrolyte; 4. Assemble the composite secondary battery in a glove box filled with argon; 5. The operating voltage window of the composite secondary battery system is 1.5 V~3.8 V.

[0037] In order to effectively evaluate the technical effect of the present invention, the cycle performance test of Example 1 was carried out, and the results are as follows: Figure 1 As shown; the discharge capacity tests of Examples 1-10 were carried out, and the results are shown in Table 1.

[0038] Table 1 Discharge capacity test results Figure 1 This is the charge and discharge cycle diagram of the composite secondary battery in Example 1. It can be seen that within the operating voltage range of 1.5 V to 3.8 V, the stability of the positive electrode structure can be guaranteed, and all the sodium ions in the positive electrode material can be ensured to participate in the intercalation and deintercalation, and the potassium ions can participate in the intercalation and deintercalation as much as possible, so that the energy release of the composite secondary battery system is fully realized, and the intercalation and deintercalation of sodium and potassium dual ions are successfully realized. The discharge specific capacity in the first week is 100.33 mAh g-1, and the capacity retention rate after 25 cycles is 92.99%.

[0039] Table 1 shows the statistical results of the discharge capacity of the composite secondary battery of each embodiment. The discharge capacity of embodiments 1-10 is above 92 mAh / g, and the highest discharge capacity is 104.54 mAh / g. x K 1-x Cr y TM 1-y O2 layered oxide material as the positive electrode, an organic electrolyte containing a sodium and potassium mixed electrolyte, supplemented by hard carbon, graphite, alloy or a combination thereof as the negative electrode, can successfully realize the function of stable charging and discharging of the composite secondary battery.

[0040] The above embodiments are only specific embodiments of the present invention, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and these obvious replacement forms all belong to the protection scope of the present invention.

Claims

1. A composite secondary battery system, comprising a positive electrode material, a negative electrode material and an electrolyte, characterized in that: The chemical formula of the positive electrode material is Na x K 1-x Cr y TM 1-y O2, wherein: x ranges from 0.25 to 0.75; y ranges from 0.9 to 1; TM is a transition metal element, and the transition metal TM is used as a doping ion, accounting for no more than 10%.

2. The composite secondary battery system according to claim 1, characterized in that: The negative electrode material is a carbon material and / or an alloy material.

3. The composite secondary battery system according to claim 1, characterized in that: The electrolyte includes: an electrolyte having both sodium ions and potassium ions and an organic solvent; and the charge and discharge potential window is 1.5 V to 3.8 V.

4. The composite secondary battery system according to claim 3, characterized in that: The organic solvent includes, but is not limited to, one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene glycol dimethyl ether, vinylene carbonate, acetonitrile, succinonitrile, and isobutyronitrile.

5. The composite secondary battery system according to claim 4, characterized in that: The sodium-containing electrolyte includes, but is not limited to, one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium bistrifluoromethanesulfonate, sodium difluorooxalatoborate, sodium bisfluorosulfonyl imide, and sodium bisoxalatoborate.

6. The composite secondary battery system according to claim 4, characterized in that: The potassium-containing electrolyte includes, but is not limited to, one or more of potassium hexafluorophosphate, potassium tetrafluoroborate, potassium perchlorate, potassium tetrafluoroborate, potassium bistrifluoromethanesulfonate, potassium difluorooxalatoborate, potassium bisfluorosulfonyl imide and potassium bisoxalatoborate.

7. The composite secondary battery system according to claim 5 or 6, characterized in that: The carbon negative electrode material is hard carbon and / or graphite.

8. The composite secondary battery system according to claim 7, characterized in that: The positive electrode material and the negative electrode material are formed into positive electrode sheets and negative electrode sheets through manufacturing, and then separated by separators and wound or stacked.

9. The composite secondary battery system according to claim 8, characterized in that: The secondary battery is a cylindrical battery or a square battery.

Images