Battery separator, method of making the same, and battery

Abstract

The application discloses a battery diaphragm, a manufacturing method thereof and a battery, and relates to the technical field of batteries. The battery diaphragm is coated with a modification layer on a diaphragm base, and the modification layer contains MnO-Ni2P / C composite material, so that the oxidation and reduction rate of short-chain LiPS and Li2S is improved, the nucleation condition and decomposition condition of Li2S are improved, and the poor infiltration characteristic of the diaphragm base and electrolyte is improved, thereby realizing high LiPS utilization rate and improving the electrochemical performance of the battery. The manufacturing method of the battery diaphragm is used for manufacturing the battery diaphragm. The battery provided by the embodiment of the application comprises the battery diaphragm or the battery diaphragm manufactured by the manufacturing method, and therefore has better electrochemical performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to battery separators, methods for manufacturing the same, and batteries. Background Technology

[0002] Lithium-sulfur (LSB) batteries have attracted widespread attention due to their high theoretical energy density and high theoretical specific capacity. The electrochemical reaction process of LSBs involves solid-liquid-solid conversion processes. During discharge, the liquid-solid conversion occurs, specifically the conversion of short-chain LiPS (lithium polysulfides) to Li₂S (lithium sulfide); during charging, the solid-liquid conversion occurs, specifically the decomposition of Li₂S. Both of these processes are rate-controlling steps, significantly limiting the improvement of LSB energy storage performance. Therefore, improvements to these reaction processes are crucial. The polypropylene separators commonly used in LSBs have poor wetting properties for ether-based electrolytes, hindering the construction of the electrochemical reaction interface and ion mass transfer, thus significantly limiting the improvement of the electrochemical performance of existing LSBs.

[0003] Therefore, this application is hereby submitted. Summary of the Invention

[0004] The purpose of this application is to provide a battery separator, a method for manufacturing the same, and a battery. Improvements to the battery separator enhance the electrochemical performance of the battery.

[0005] This application is implemented as follows:

[0006] In a first aspect, this application provides a battery separator, comprising:

[0007] Diaphragm substrate;

[0008] A modification layer is coated on the surface of the membrane substrate, and the modification layer contains MnO-Ni2P / C composite material.

[0009] In an optional embodiment, the thickness of the diaphragm substrate is 20–30 μm.

[0010] In an optional embodiment, the thickness of the modification layer is 10–15 μm.

[0011] In an optional embodiment, the molar ratio of Mn to Ni in the MnO-Ni2P / C composite material is 2 to 2.5:1.

[0012] In an optional embodiment, the modification layer further includes a conductive agent and a binder.

[0013] In an optional embodiment, the mass ratio of the MnO-Ni2P / C composite material, the conductive agent, and the binder is 4-8:2-4:1; further, the mass ratio is 6:3:1.

[0014] In an optional embodiment, the conductive agent is carbon black, and / or the binder is polyvinylidene fluoride.

[0015] Secondly, this application provides a method for manufacturing the battery separator according to any of the foregoing embodiments, comprising:

[0016] A metal source solution containing manganese and nickel sources is mixed with a potassium citrate solution and then evaporated and crystallized to obtain a precursor material.

[0017] The precursor material was calcined to obtain the MnO-Ni / C composite material;

[0018] The MnO-Ni / C composite material was calcined with sodium hypophosphite under a protective gas atmosphere to obtain the MnO-Ni2P / C composite material.

[0019] A slurry was prepared using MnO-Ni2P / C composite material, coated onto a separator substrate, and dried to obtain a battery separator.

[0020] In an optional embodiment, the manganese source is manganese nitrate and the nickel source is nickel nitrate.

[0021] In an optional embodiment, the step of mixing a metal source solution containing manganese and nickel sources with a potassium citrate solution and evaporating and crystallizing to obtain the precursor material includes:

[0022] Dissolve manganese nitrate solution and nickel nitrate hexahydrate in water to obtain the first solution;

[0023] The first solution was added dropwise to the potassium citrate solution and stirred at room temperature to obtain a mixed solution;

[0024] The mixed solution was heated in a water bath to evaporate and crystallize, thus obtaining the precursor material.

[0025] In an optional embodiment, the step of calcining the precursor material to obtain the MnO-Ni / C composite material includes:

[0026] Under a protective gas atmosphere, the precursor material is heated to 180–250°C and held at that temperature for 0.5–1.5 hours.

[0027] Then raise the temperature to 750–850℃ and hold for 1.5–3 hours;

[0028] The temperature was then lowered to 450–550°C, and then cooled to room temperature along with the furnace.

[0029] The calcined product was washed and dried to obtain the MnO-Ni / C composite material.

[0030] In an optional embodiment, the step of calcining the MnO-Ni / C composite material with sodium hypophosphite under a protective gas atmosphere to obtain the MnO-Ni2P / C composite material includes:

[0031] The MnO-Ni / C composite material and sodium hypophosphite were placed in a heating furnace, and a protective gas was introduced into the heating furnace. The sodium hypophosphite was located upstream of the MnO-Ni / C composite material along the flow direction of the protective gas.

[0032] Control the heating furnace temperature to 350–400℃ and maintain it for 2.5–3.5 hours;

[0033] The furnace was cooled to room temperature to obtain the MnO-Ni2P / C composite material.

[0034] In an optional embodiment, the steps of preparing a slurry using a MnO-Ni2P / C composite material, coating the slurry onto a separator substrate, and drying it to obtain a battery separator include:

[0035] The MnO-Ni2P / C composite material, conductive agent, and binder are mixed and ground to obtain a mixture;

[0036] The mixture is combined with a dispersant to obtain a slurry;

[0037] The slurry is coated onto the separator substrate and dried at 50–70°C for 3–8 hours to obtain the battery separator.

[0038] In an optional embodiment, the dispersant is N-methylpyrrolidone.

[0039] Thirdly, this application provides a battery, including a casing, a battery cell, and an electrolyte, wherein the battery cell and the electrolyte are placed inside the casing; the battery cell includes a positive electrode, a battery separator, and a negative electrode stacked together, wherein the battery separator in the battery cell is a battery separator of any of the aforementioned first aspects or a battery separator produced by any of the aforementioned second aspects.

[0040] In an alternative embodiment, the modification layer on the battery separator faces the positive electrode.

[0041] This application has the following beneficial effects:

[0042] The battery separator provided in this application improves the redox rate of short-chain LiPS and Li2S by coating a modification layer on the separator substrate. The modification layer contains MnO-Ni2P / C composite material, which improves the nucleation and decomposition of Li2S and improves the poor wetting characteristics between the separator substrate and the electrolyte, thereby achieving high LiPS utilization and improving the electrochemical performance of the battery.

[0043] The battery separator manufacturing method provided in this application embodiment is used to manufacture the battery separator described above; the battery provided in this application embodiment includes the battery separator described above or the battery separator obtained by the above manufacturing method, and therefore has better electrochemical performance. Attached Figure Description

[0044] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 This is a schematic diagram of the battery separator in one embodiment of this application;

[0046] Figure 2 This is a flowchart of a method for manufacturing a battery separator in one embodiment of this application.

[0047] Explanation of key component symbols: 100 - battery separator; 110 - separator substrate; 120 - modification layer. Detailed Implementation

[0048] Because the polypropylene separators commonly used in existing lithium-sulfur batteries have poor wetting properties for ether-based electrolytes, this hinders the construction of electrochemical reaction interfaces and ion mass transfer, significantly limiting the improvement of the electrochemical performance of existing lithium-sulfur batteries. To address the poor electrochemical performance of existing lithium-sulfur batteries, this application provides a battery separator and its fabrication method. By setting a modification layer on the battery separator, the redox rates of short-chain LiPS and Li2S are increased, the nucleation and decomposition of Li2S are improved, and the poor wetting properties between the separator substrate and the electrolyte are mitigated, thereby achieving high LiPS utilization and improving the battery's electrochemical performance.

[0049] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0050] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0051] Figure 1 This is a schematic diagram of the battery separator 100 in one embodiment of this application. Figure 1As shown, the battery separator 100 provided in this embodiment includes a separator substrate 110 and a modification layer 120 coated on the surface of the separator substrate 110. The separator substrate 110 can be made of existing separator materials, such as polypropylene (PP). The modification layer 120 contains a MnO-Ni2P / C composite material.

[0052] Furthermore, the modification layer 120 also includes a conductive agent and a binder; the mass ratio of the MnO-Ni2P / C composite material, the conductive agent, and the binder is 4-8:2-4:1. Optionally, the mass ratio of the MnO-Ni2P / C composite material, the conductive agent, and the binder is 6:3:1.

[0053] Optionally, the molar ratio of Mn to Ni in the MnO-Ni2P / C composite material is 2 to 2.5:1.

[0054] Optionally, the conductive agent is carbon black and the binder is polyvinylidene fluoride (PVDF).

[0055] Optionally, the thickness of the membrane substrate 110 is 20–30 μm, and the thickness of the modification layer 120 is 10–15 μm.

[0056] In this embodiment, the modification layer 120 can be disposed on one side of the separator substrate 110, and the modification layer 120 is oriented towards the positive electrode. In the MnO-Ni2P / C composite material, MnO is responsible for adsorbing lithium polysulfides (mainly Li2S8) and lowering the decomposition barrier of Li2S; Ni2P is responsible for adsorbing the lithium polysulfides (mainly Li2S6 and Li2S4) converted from MnO adsorption, and also mainly catalyzes the conversion of lithium polysulfides. MnO and Ni2P together improve the poor wettability of the electrolyte to the separator substrate 110, thereby ultimately improving the cycle stability and rate performance of the lithium-sulfur battery.

[0057] The battery separator manufacturing method provided in this application embodiment can be used to manufacture the battery separator 100 described above. Figure 2 This is a flowchart illustrating a method for fabricating a battery separator according to one embodiment of this application. Figure 2 As shown, the method for manufacturing the battery separator provided in this application embodiment includes:

[0058] In step S100, a metal source solution containing manganese and nickel sources is mixed with a potassium citrate solution and evaporated to crystallize in order to obtain a precursor material.

[0059] Optionally, the manganese source is manganese nitrate, and the nickel source is nickel nitrate; further, step S100 may specifically include:

[0060] Step S110: Dissolve manganese nitrate solution and nickel nitrate hexahydrate in water to obtain the first solution;

[0061] Step S120: The first solution is added dropwise to the potassium citrate solution and stirred at room temperature to obtain a mixed solution;

[0062] Step S130: The mixed solution is heated in a water bath to evaporate and crystallize to obtain the precursor material.

[0063] Optionally, the molar ratio of potassium citrate to the metal source is 10:1, and the molar ratio of manganese source to nickel source is 2:1.

[0064] Step S200: The precursor material is calcined to obtain the MnO-Ni / C composite material.

[0065] Optionally, step S200 includes: heating the precursor material to 180–250°C under a protective gas atmosphere and holding it at that temperature for 0.5–1.5 h; then raising the temperature to 750–850°C and holding it for 1.5–3 h; then cooling the temperature to 450–550°C and then cooling it to room temperature in the furnace; washing and drying the calcined product to obtain the MnO-Ni / C composite material. Optionally, a tube furnace is used to heat the precursor material, and argon can be selected as the protective gas; deionized water can be used for washing, and a vacuum drying oven can be used for drying.

[0066] In step S300, the MnO-Ni / C composite material and sodium hypophosphite are calcined under a protective gas atmosphere to obtain the MnO-Ni2P / C composite material.

[0067] Optionally, step S300 includes:

[0068] Step S310: Place the MnO-Ni / C composite material and sodium hypophosphite in a heating furnace, and introduce a protective gas into the heating furnace. Along the flow direction of the protective gas, the sodium hypophosphite is located upstream of the MnO-Ni / C composite material.

[0069] Step S320: Control the heating furnace to heat to 350-400℃ and maintain the temperature for 2.5-3.5 hours;

[0070] In step S330, the furnace is cooled to room temperature to obtain the MnO-Ni2P / C composite material.

[0071] In step S310, the protective gas can be argon; the MnO-Ni / C composite material can be placed on one side of the ceramic boat, and the sodium hypophosphite can be placed on the other side of the ceramic boat. The mass ratio of sodium hypophosphite to MnO-Ni / C composite material can be 10:1. The ceramic boat is placed in a tube furnace, with the side of sodium hypophosphite close to the upper gas flow port.

[0072] In step S400, a slurry is prepared using MnO-Ni2P / C composite material, coated onto the separator substrate, and dried to obtain the battery separator.

[0073] Optionally, step S400 may include:

[0074] Step S410: Mix and grind the MnO-Ni2P / C composite material, conductive agent, and binder to obtain a mixture;

[0075] Step S420: Mix the mixture with a dispersant to obtain a slurry;

[0076] In step S430, the slurry is coated onto the separator substrate 110 and dried at 50-70°C for 3-8 hours to obtain the battery separator 100.

[0077] In step S410, the conductive agent can be carbon black, and the binder can be polyvinylidene fluoride (PVDF). In step S420, the dispersant can be N-methylpyrrolidone. The membrane substrate 110 can be an existing PP membrane, such as the Celgard 2500 membrane.

[0078] The battery (not shown in the figure) provided in this application embodiment includes a casing, a battery cell, and an electrolyte, with the battery cell and electrolyte disposed within the casing. The battery cell includes a positive electrode, a battery separator 100, and a negative electrode stacked together. The battery separator 100 in the battery cell is the aforementioned battery separator 100 or a battery separator 100 manufactured by the aforementioned method. This battery can be a lithium-sulfur battery. Furthermore, the modification layer 120 on the battery separator 100 faces the positive electrode.

[0079] The beneficial effects of the battery separator 100 of this application will be described in detail below with reference to embodiments, comparative examples and tests.

[0080] Example 1

[0081] This embodiment provides a method for manufacturing a battery separator, which specifically includes the following steps:

[0082] (1) Weigh potassium citrate into a first beaker and dissolve it in deionized water; weigh manganese nitrate solution (50 wt%) and nickel nitrate hexahydrate into a second beaker and dissolve them in deionized water by sonication; after both are dissolved, add the solution from the second beaker dropwise to the first beaker, mix and stir at room temperature for 3 hours, then place it in a constant temperature water bath at 80°C to evaporate and crystallize to obtain the precursor material. The molar ratio of potassium citrate to the metal source is 10:1, and the molar ratio of manganese source to nickel source is 2:1.

[0083] (2) The precursor material obtained in step (1) was placed in a tube furnace and calcined under an argon atmosphere. First, the temperature was increased to 200℃ at a heating rate of 2℃ / min and held for 1 hour; then, the temperature was increased to 800℃ at a heating rate of 2℃ / min and held for 2 hours. After the holding period, the temperature was reduced to 500℃ at a cooling rate of 5℃ / min, and finally cooled to room temperature with the tube furnace. The calcined material was washed with deionized water and dried in a vacuum drying oven at 60℃ to obtain the MnO-Ni / C composite material.

[0084] (3) Place the MnO-Ni / C composite material obtained in step (2) on one side of the ceramic boat, weigh sodium hypophosphite and place it on the other side of the ceramic boat. The mass ratio of sodium hypophosphite to MnO-Ni / C composite material is 10:1. Place the entire ceramic boat in a tube furnace, with the side of sodium hypophosphite close to the upper gas flow port. Calcinate in an argon atmosphere, raise the temperature to 375℃ at a heating rate of 2℃ / min and hold for 3h. After the holding period, cool the furnace to room temperature to obtain the final MnO-Ni2P / C composite material.

[0085] (4) The MnO-Ni2P / C composite material, conductive carbon black and PVDF obtained in step (3) are mixed in an agate mortar in a mass ratio of 6:3:1 and ground until the particles are fine and evenly dispersed. Then, the mixture is transferred to a beaker and N-methylpyrrolidone is added to adjust the viscosity so that the slurry has a certain fluidity. The slurry is coated on the surface of the separator substrate using a 100μm scraper and dried in a 60℃ drying oven for 6 hours to obtain the battery separator.

[0086] Comparative Example 1

[0087] The difference from Example 1 is that steps (1) to (3) related to the preparation of MnO-Ni2P / C composite material are omitted, and in step (4), MnO-Ni2P / C composite material is replaced with MnO / C material.

[0088] Comparative Example 2

[0089] The difference from Example 1 is that steps (1) to (3) related to the preparation of MnO-Ni2P / C composite material are omitted, and in step (4), MnO-Ni2P / C composite material is replaced with Ni2P / C material.

[0090] Comparative Example 3

[0091] The difference from Example 1 is that steps (1) to (3) related to the preparation of MnO-Ni2P / C composite material are omitted, and in step (4), MnO-Ni2P / C composite material is replaced with MnO-Ni / C.

[0092] Button batteries were assembled in a glove box using the battery separators from Examples 1 and Comparative Examples 1-3. Specifically, elemental sulfur, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 6:3:1 and coated to form a positive electrode. A lithium sheet was used as the negative electrode. The battery separators prepared in Examples 1 and Comparative Examples 1-3 were used as the battery separators, respectively. A lithium bis(trifluoromethanesulfonyl)imide solution (DOL and DME as solvents) was used as the electrolyte. The modified layer of the battery separator faced the positive electrode.

[0093]

[0094] The assembled batteries were tested, and the results are shown in the table below.

[0095] As shown in the table above, the lithium-sulfur battery assembled using the battery separator of Example 1 exhibits higher specific capacity and better cycle performance even at low E / S conditions. This can be attributed to the improved electrochemical reaction activity interface resulting from the improved wetting properties of the electrolyte and battery separator, and also to the synergistic effect of MnO and Ni2P.

[0096] Other test results are shown in the table below.

[0097]

[0098]

[0099] As can be seen from the table above, the lithium-sulfur battery assembled using the separator of Example 1 has a higher reversible specific capacity even at low E / S and high rate.

[0100] As can be seen, the battery separator provided in this application embodiment can achieve the following beneficial effects:

[0101] (1) The MnO-Ni2P / C composite material is coated on the surface of the separator substrate as a functional material. The appropriate adsorption strength of MnO for lithium polysulfide and the catalytic conversion of lithium polysulfide by Ni2P are utilized to improve the utilization rate of active material sulfur, that is, to improve the battery capacity.

[0102] (2) After the MnO-Ni2P / C composite material is coated on the surface of the separator substrate, since both MnO and Ni2P are polar substances, the wetting ability of the electrolyte to the battery separator is significantly improved. This optimizes the electrochemical reaction interface and enhances the mass transfer ability of ions, which increases the concentration of polysulfides and the concentration of solvated lithium ions at the interface between the battery separator and the positive electrode electrolyte. This enhances the conversion rate and reaction depth of lithium polysulfides, which is beneficial to improving the rate performance of the battery, especially the electrochemical performance of the battery under low electrolyte conditions.

[0103] (3) In the MnO-Ni2P / C composite material, Ni2P can capture other Li2S8 after MnO adsorption saturation through PS bonds and P-Li bonds on the one hand; and capture Li2S6 and Li2S4 after adsorption and transformation on the MnO surface on the other hand, so as to facilitate the catalytic transformation of Li2S4 on the Ni2P surface.

[0104] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for manufacturing a battery separator, characterized in that, The battery separator includes a separator substrate and a modification layer. The modification layer is coated on the surface of the separator substrate and contains a MnO-Ni2P / C composite material. The method for manufacturing the battery separator includes: A metal source solution containing manganese and nickel sources is mixed with a potassium citrate solution and then evaporated and crystallized to obtain a precursor material. The precursor material is calcined to obtain a MnO-Ni / C composite material; The MnO-Ni / C composite material was calcined with sodium hypophosphite under a protective gas atmosphere to obtain the MnO-Ni2P / C composite material. A slurry is prepared using the MnO-Ni2P / C composite material, coated onto a separator substrate, and dried to obtain the battery separator.

2. The manufacturing method according to claim 1, characterized in that, The manganese source is manganese nitrate, and the nickel source is nickel nitrate; The steps of mixing a metal source solution containing manganese and nickel sources with a potassium citrate solution and evaporating and crystallizing to obtain the precursor material include: Dissolve manganese nitrate solution and nickel nitrate hexahydrate in water to obtain the first solution; The first solution was added dropwise to a potassium citrate solution and stirred at room temperature to obtain a mixed solution; The mixed solution is heated in a water bath to evaporate and crystallize, thereby obtaining the precursor material.

3. The manufacturing method according to claim 1, characterized in that, The step of calcining the precursor material to obtain the MnO-Ni / C composite material includes: Under a protective gas atmosphere, the precursor material is heated to 180~250℃ and held at that temperature for 0.5~1.5h. Then raise the temperature to 750~850℃ and keep it warm for 1.5~3 hours; The temperature was then lowered to 450-550℃, and then cooled to room temperature along with the furnace. The calcined product was washed and dried to obtain the MnO-Ni / C composite material.

4. The manufacturing method according to claim 1, characterized in that, The step of calcining the MnO-Ni / C composite material with sodium hypophosphite under a protective gas atmosphere to obtain the MnO-Ni2P / C composite material includes: The MnO-Ni / C composite material and the sodium hypophosphite are placed in a heating furnace, and a protective gas is introduced into the heating furnace. Along the flow direction of the protective gas, the sodium hypophosphite is located upstream of the MnO-Ni / C composite material. The heating furnace is heated to 350~400℃ and held at that temperature for 2.5~3.5 hours. The furnace was cooled to room temperature to obtain the MnO-Ni2P / C composite material.

5. The manufacturing method according to claim 1, characterized in that, The steps of preparing a slurry using the MnO-Ni2P / C composite material, coating the slurry onto a separator substrate, and drying it to obtain the battery separator include: The MnO-Ni2P / C composite material, conductive agent, and binder are mixed and ground to obtain a mixture; The mixture is combined with a dispersant to obtain the slurry; The slurry is coated onto the separator substrate and dried at 50-70°C for 3-8 hours to obtain the battery separator.

6. The manufacturing method according to any one of claims 1-5, characterized in that, The thickness of the diaphragm substrate is 20~30μm.

7. The manufacturing method according to claim 6, characterized in that, The thickness of the modified layer is 10~15μm.

8. The manufacturing method according to any one of claims 1-5, characterized in that, The molar ratio of Mn to Ni in the MnO-Ni2P / C composite material is 2~2.5:

1.

9. The manufacturing method according to any one of claims 1-5, characterized in that, The modified layer also includes a conductive agent and a binder; the mass ratio of the MnO-Ni2P / C composite material, the conductive agent, and the binder is 4-8:2-4:

1.

10. A battery, characterized in that, The device includes a housing, a battery cell, and an electrolyte, wherein the battery cell and the electrolyte are disposed within the housing; the battery cell includes a positive electrode, a battery separator, and a negative electrode stacked together, wherein the battery separator in the battery cell is a battery separator prepared by the manufacturing method of any one of claims 1-9.

11. The battery according to claim 10, characterized in that, The modification layer on the battery separator faces the positive electrode.

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