A composite separator for a semi-solid battery and a preparation method thereof

Abstract

The present invention relates to the technical field of diaphragms for batteries, and discloses a composite diaphragm for a semi-solid battery and a preparation method thereof. The composite diaphragm comprises an ABA three-layer structure obtained by co-extrusion of three layers; the raw material of the B layer comprises polypropylene; by mass percentage, the raw materials of the A layer are 85-95% of PEO, 0-5% of Zn-MOF material and the remaining Zn-MOF-derived carbon material; the Zn-MOF-derived carbon material is prepared by calcining the Zn-MOF material at 900-1200 °C in an inert atmosphere for 3-6 h. Through the structural design and raw material ratio of the diaphragm, the present invention improves the ion transport efficiency and battery energy density on the premise of ensuring the safety of the product, and can also reduce the usage amount of the liquid electrolyte, further enhancing the battery safety.

Description

Technical Field

[0001] The present invention relates to the technical field of diaphragms for batteries, and in particular to a composite diaphragm for a semi-solid battery and a preparation method thereof. Background Art

[0002] Since the ionic conductivity of most current solid electrolytes is lower than that of liquid electrolytes, this may lead to a relatively high internal resistance of the battery, affecting its power density. At the same time, the interfacial stability between the solid electrolyte and the electrode material is a challenge, and the interfacial impedance may cause a decline in battery performance. Moreover, the processing technologies of solid electrolytes and electrodes are not yet mature, and the manufacturing process may be complex and costly, which limits the large-scale application of solid-state batteries. Before significant breakthroughs are made in the interfacial problems and manufacturing costs of solid-state batteries, semi-solid batteries are the only way at this stage and the optimal solution under the current environment considering factors such as comprehensive costs and market choices.

[0003] As a semi-solid battery that does not completely abandon liquid electrolytes, the diaphragm plays an important role in the semi-solid battery and is an important component thereof. Solid polymer electrolyte (SPE), also known as ion-conducting polymer. The research on solid polymer electrolytes began in 1973 with the discovery of the conductivity of complexes of polyethylene oxide (PEO) and alkali metal ions by Wright et al. In 1979, Armand et al. in France reported that the ionic conductivity of PEO alkali metal salt complexes reached 10 -5 S / cm at 40 - 60 °C, and it has good film-forming properties and can be used as an electrolyte for lithium-ion batteries. Replacing traditional liquid electrolytes with solid electrolytes is expected to fundamentally solve the safety problems of batteries. However, solid electrolytes still have problems such as low mechanical strength and poor wettability, which limit their application in diaphragms. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a composite diaphragm for a semi-solid battery and a preparation method thereof. The diaphragm adopts an ABA three-layer structure. The A layer uses a Zn-MOF-derived carbon material and polyethylene oxide, which can synergistically improve the ionic conductivity of the electrolyte. The use of polymer solid electrolyte can also reduce the usage amount of liquid electrolyte and further enhance battery safety. The B layer uses a polypropylene material, which can endow the diaphragm with strong mechanical properties, making the overall composite diaphragm have sufficient puncture strength and tensile strength, and thus obtaining a composite diaphragm with better overall performance.

[0005] The object of the present invention is achieved through the following technical solutions:

[0006] In a first aspect, the present invention provides a composite separator for a semi-solid battery. The composite separator includes an ABA three-layer structure obtained by co-extrusion of three layers; the raw material of the B layer includes polypropylene; by mass percentage, the raw material of the A layer is 85-95% of PEO, 0-5% of Zn-MOF material, and the remaining Zn-MOF-derived carbon material; the Zn-MOF-derived carbon material is obtained by calcining the Zn-MOF material at 900-1200 °C in an inert atmosphere for 3-6 h.

[0007] The composite separator in the present invention has an ABA three-layer structure. The A layer (upper and lower surface layers) uses Zn-MOF-derived carbon material and polyethylene oxide (PEO). As a polymer solid electrolyte, PEO can reduce the usage amount of liquid electrolyte and improve the overall energy density of the battery at the same time. Since the Zn-MOF-derived carbon material is obtained by high-temperature anaerobic calcination of the Zn-MOF material, the Zn element in the framework can be removed, and only the MOF skeleton structure is retained. It can also avoid the risk of degradation of the MOF composed of redox elements (Zn) near the electrode interface. And due to the vaporization and escape of Zn in the calcined MOF skeleton, defect structures will appear, so more active sites will be provided during the entire electrochemical process, greatly shortening the ion transport path and promoting the progress of the electrochemical reaction. At the same time, mixing the Zn-MOF-derived carbon material with PEO can prevent the recombination of PEO, reduce its crystal phase ratio, improve the movement of PEO chains, and increase the ionic conductivity of the electrolyte.

[0008] In addition, the raw material of the A layer (upper and lower surface layers) can also use Zn-MOF-derived carbon material, Zn-MOF material and polyethylene oxide (PEO). Adding a certain amount of Zn-MOF material can cooperate with the Zn-MOF-derived carbon material. The Zn-MOF and its derived carbon material particles are distributed in the PEO matrix as cross-linking centers, which can prevent the recombination of PEO. However, when the addition amount of the Zn-MOF material is too much, even if the Zn-MOF-derived carbon material is added, it is impossible to well reduce the influence of the redox problem existing in the Zn-MOF material during the reaction and the disintegration problem existing during long-term charge and discharge, resulting in a lower capacity retention rate of the battery.

[0009] The B layer uses polypropylene material. The properties of the polypropylene material itself endow the separator with strong mechanical properties, making the overall composite separator have sufficient puncture strength and tensile strength, and having a sufficient safety factor during battery testing. At the same time, using polypropylene material with a low melt index can reduce the thickness of the overall separator as much as possible while ensuring the mechanical strength, which is beneficial to the lightweight of the battery.

[0010] Through the structural design of the separator and the raw material ratio, on the premise of ensuring sufficient mechanical strength of the separator, by introducing a polymer solid electrolyte and co-extruding it with the base film in the form of a film layer, the phenomenon of coating peeling that easily occurs when coating the solid electrolyte on the film surface is alleviated to a certain extent. Moreover, the use of the polymer solid electrolyte can increase the energy density of the battery and also reduce the usage amount of the liquid electrolyte, further enhancing the battery safety.

[0011] Preferably, in the ABA three-layer structure, the thickness ratio of the A layer, the B layer, and the A layer is 10-20%: 60-80%: 10-20%, and the thicknesses of the upper and lower A layers are the same. More preferably, in the ABA three-layer structure, the thickness ratio of the A layer, the B layer, and the A layer is 10-15%: 70-80%: 10-15%, and the thicknesses of the upper and lower A layers are the same.

[0012] Preferably, the thickness of the composite separator is 12-20 μm.

[0013] Preferably, the melt index of the polypropylene is 0.8-1.0 g / 10min.

[0014] Preferably, the mass percentage of the Zn-MOF material added is not greater than the mass percentage of the Zn-MOF-derived carbon material added.

[0015] Preferably, the heating rate during the calcination is 10-15 °C / min.

[0016] Preferably, the inert atmosphere is a nitrogen and / or argon atmosphere.

[0017] In a second aspect, the present invention provides a method for preparing a composite separator for a semi-solid battery, comprising the following steps:

[0018] (1) Under an inert atmosphere environment, calcine the Zn-MOF material at 900-1200 °C for 3-6 h to obtain a Zn-MOF-derived carbon material;

[0019] (2) After mixing the raw materials of the A layer and the B layer respectively in proportion, obtain a cast sheet through three-layer co-extrusion and cooling traction;

[0020] (3) Subject the cast sheet to heat treatment, longitudinal cold stretching, longitudinal hot stretching, and heat setting in sequence to obtain a composite separator for a semi-solid battery.

[0021] Preferably, the preparation of the Zn-MOF material comprises the following steps: Add zinc nitrate hexahydrate and 2-methylimidazole to a mixed solution of methanol and ethanol, stir and then let stand, and then filter and dry to obtain the Zn-MOF material.

[0022] Preferably, the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:10 - 11; the standing time is 30 - 50 min.

[0023] Preferably, in the mixed solution of methanol and ethanol, the volume ratio of methanol to ethanol is 1:1.

[0024] Preferably, the extrusion temperature of the three-layer co-extrusion is 200 - 240 °C.

[0025] Preferably, the cooling temperature is 80 - 100 °C; the traction speed is 40 - 80 m / min.

[0026] Preferably, the heat treatment temperature is 110 - 150 °C, and the time is 10 - 30 h.

[0027] Preferably, the temperature of the longitudinal cold stretching is 50 - 100 °C, and the stretching ratio is 1.1 - 1.5.

[0028] Preferably, the temperature of the longitudinal hot stretching is 140 - 170 °C, and the stretching ratio is 1.7 - 2.2.

[0029] Preferably, the heat setting temperature is 130 - 140 °C, the stretching ratio is 0.9 - 1.2, and the time is 1 - 10 min.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) Through the structural design of the separator and the raw material ratio, on the premise of ensuring the safety of the product, the ion transport efficiency of the product is improved, the usage amount of the electrolyte required for preparing the battery is reduced, and the performance requirements of the separator in multiple fields such as energy storage and power can be satisfied simultaneously.

[0032] (2) The lithium-ion battery separator for semi-solid batteries prepared by the preparation method described in this patent has a puncture performance greater than 350 gf, a thickness of 12 - 20 μm, a tensile strength in the MD direction greater than 150 MPa, a tensile strength in the TD direction greater than 14 MPa, an air permeability not greater than 400 s / 100 mL, and a capacity retention rate of the battery not less than 90% after 100 cycles. Detailed Embodiments

[0033] The following specific examples are used to illustrate the technical solutions of the present invention, but the protection scope of the present invention is not limited thereto.

[0034] Example 1

[0035] The composite separator for semi-solid batteries includes an ABA three-layer structure with a total thickness of 18 μm.

[0036] A layer: The thickness is 1.8 μm (10% of the total thickness), and the thickness of the upper and lower A layers is the same; in terms of mass percentage, the raw materials of the A layer are 90% PEO and 10% Zn-MOF-derived carbon material.

[0037] Layer B: thickness is 14.4 μm (80% of the total thickness); the raw material of layer B is polypropylene material with a low melt index (0.8-1.0 g / 10min).

[0038] The preparation of the composite diaphragm for the semi-solid battery comprises the following steps:

[0039] (1) Zinc nitrate hexahydrate and 2-methylimidazole were added to a mixture of methanol and ethanol (volume ratio of 1:1) in a molar ratio of 1:10, stirred thoroughly and allowed to stand for 30 minutes, then filtered, washed with ethanol and water, dried and ground to obtain Zn-MOF material. In a nitrogen atmosphere, the Zn-MOF material was placed in a muffle furnace, heated at a rate of 10°C / min, heated to 900°C and calcined for 4 hours to obtain a Zn-MOF-derived carbon material.

[0040] (2) The raw materials of layer A are put into a mixing silo in proportion for mixing, and then put into a first twin-screw extruder; the raw materials of layer B are put into a second twin-screw extruder; the extrusion volume ratio of the first twin-screw extruder (including the upper and lower A layers) and the second twin-screw extruder is set to 2:8, and the extruder temperature is adjusted to 210°C. After melting, the materials are filtered, and the materials extruded by the first twin-screw extruder are used as the A layer, and the materials extruded by the second twin-screw extruder are used as the B layer, and are extruded through a three-layer die; the melt extruded through the die is cooled at a temperature of 100°C, and is pulled at a pulling speed of 60m / min to obtain a three-layer composite casting sheet.

[0041] (3) The cast sheet was heat treated at 135°C for 18 h; then the heat treated cast sheet was firstly cold stretched longitudinally at 85°C with a stretching ratio of 1.2, then hot stretched longitudinally at 140°C with a stretching ratio of 2.0, and then heat set at 140°C for 4 min with a heat setting stretching ratio of 0.98, thereby obtaining a composite separator for a semi-solid battery.

[0042] Example 2

[0043] The difference from Example 1 is that the raw material of layer A uses 85% PEO and 15% Zn-MOF derived carbon material.

[0044] The composite separator for semi-solid batteries includes an ABA three-layer structure with a total thickness of 18μm.

[0045] Layer A: The thickness is 1.8 μm (the thickness is 10% of the total thickness), and the thicknesses of the upper and lower Layer A are the same; by mass percentage, the raw materials of Layer A are 85% PEO and 15% Zn-MOF-derived carbon material.

[0046] Layer B: The thickness is 14.4 μm (the thickness is 80% of the total thickness); the raw material of Layer B is a polypropylene material with a low melt index (0.8 - 1.0 g / 10min).

[0047] The preparation of the composite separator for the semi-solid battery includes the following steps:

[0048] (1) Zinc nitrate hexahydrate and 2-methylimidazole were added to a mixed solution of methanol and ethanol (volume ratio 1:1) at a molar ratio of 1:10, stirred well and left to stand for 30 min, then filtered by suction, washed with ethanol and water respectively, and dried and ground to obtain Zn-MOF material. Under a nitrogen atmosphere, the Zn-MOF material was placed in a muffle furnace and heated at a rate of 10 °C / min to 900 °C and calcined for 4 h to obtain Zn-MOF-derived carbon material.

[0049] (2) The raw materials of Layer A were mixed in proportion in a mixing bin and then put into the first twin-screw extruder; the raw materials of Layer B were put into the second twin-screw extruder; the extrusion ratio of the first twin-screw extruder (including the upper and lower Layer A) to the second twin-screw extruder was set to 2:8, the temperature of the extruder was adjusted to 210 °C, melted and then filtered. The material extruded from the first twin-screw extruder was used as Layer A, and the material extruded from the second twin-screw extruder was used as Layer B, and they were co-extruded through a three-layer die. The melt extruded from the die was cooled at a temperature of 100 °C and drawn at a traction speed of 60 m / min to obtain a three-layer composite cast sheet.

[0050] (3) The cast sheet was heat-treated at a temperature of 135 °C for 18 h; immediately after that, the heat-treated cast sheet was first longitudinally cold-drawn at a temperature of 85 °C with a draw ratio of 1.2, then longitudinally hot-drawn at a temperature of 140 °C with a draw ratio of 2.0, and then heat-set at a temperature of 140 °C for 4 min with a heat-set draw ratio of 0.98 to obtain the composite separator for the semi-solid battery.

[0051] Example 3

[0052] The difference from Example 1 is that the raw materials of Layer A used 95% PEO and 5% Zn-MOF-derived carbon material.

[0053] The composite separator for the semi-solid battery includes an ABA three-layer structure with a total thickness of 18 μm.

[0054] Layer A: The thickness is 1.8 μm (the thickness is 10% of the total thickness), and the thicknesses of the upper and lower Layer A are the same; by mass percentage, the raw materials of Layer A are 95% PEO and 5% Zn-MOF-derived carbon material.

[0055] Layer B: The thickness is 14.4 μm (the thickness is 80% of the total thickness); the raw material of Layer B is a polypropylene material with a low melt index (0.8 - 1.0 g / 10min).

[0056] The preparation of the composite separator for the semi-solid battery includes the following steps:

[0057] (1) Zinc nitrate hexahydrate and 2-methylimidazole were added to a mixed solution of methanol and ethanol (volume ratio 1:1) at a molar ratio of 1:10, stirred well and left standing for 30 min, then filtered by suction, washed with ethanol and water respectively, and dried and ground to obtain Zn-MOF material. In a nitrogen atmosphere, the Zn-MOF material was placed in a muffle furnace and heated at a rate of 10 °C / min, and calcined at 900 °C for 4 h to obtain Zn-MOF-derived carbon material.

[0058] (2) The raw materials of Layer A were proportionally fed into a mixing bin for mixing, and then put into the first twin-screw extruder; the raw materials of Layer B were put into the second twin-screw extruder; the extrusion amount ratio of the first twin-screw extruder (including the upper and lower Layer A) and the second twin-screw extruder was set to 2:8, the extrusion temperature of the extruder was adjusted to 210 °C, melted and then filtered. The material extruded from the first twin-screw extruder was used as Layer A, and the material extruded from the second twin-screw extruder was used as Layer B, and co-extruded through a three-layer die. The melt extruded from the die was cooled at a temperature of 100 °C and drawn at a traction speed of 60 m / min to obtain a three-layer composite cast sheet.

[0059] (3) The cast sheet was heat-treated at a temperature of 135 °C for 18 h; immediately afterwards, the heat-treated cast sheet was first longitudinally cold-drawn at a temperature of 85 °C with a draw ratio of 1.2, then longitudinally hot-drawn at a temperature of 140 °C with a draw ratio of 2.0, and then heat-set at a temperature of 140 °C for 4 min with a heat-set draw ratio of 0.98 to obtain the composite separator for the semi-solid battery.

[0060] Example 4

[0061] The difference from Example 1 is that the raw materials of Layer A used are 85% PEO, 10% Zn-MOF-derived carbon material and 5% Zn-MOF material.

[0062] The composite separator for the semi-solid battery includes a three-layer ABA structure with a total thickness of 18 μm.

[0063] A layer: The thickness is 1.8 μm (10% of the total thickness), and the thickness of the upper and lower A layers is the same; in terms of mass percentage, the raw materials of the A layer are 85% PEO, 10% Zn-MOF-derived carbon material and 5% Zn-MOF material.

[0064] Layer B: thickness is 14.4 μm (80% of the total thickness); the raw material of layer B is polypropylene material with a low melt index (0.8-1.0 g / 10min).

[0065] The preparation of the composite diaphragm for the semi-solid battery comprises the following steps:

[0066] (1) Zinc nitrate hexahydrate and 2-methylimidazole were added to a mixture of methanol and ethanol (volume ratio of 1:1) in a molar ratio of 1:10, stirred thoroughly and allowed to stand for 30 minutes, then filtered, washed with ethanol and water, dried and ground to obtain Zn-MOF material. In a nitrogen atmosphere, the Zn-MOF material was placed in a muffle furnace, heated at a rate of 10°C / min, heated to 900°C and calcined for 4 hours to obtain a Zn-MOF-derived carbon material.

[0067] (2) The raw materials of layer A are put into a mixing silo in proportion for mixing, and then put into a first twin-screw extruder; the raw materials of layer B are put into a second twin-screw extruder; the extrusion volume ratio of the first twin-screw extruder (including the upper and lower A layers) and the second twin-screw extruder is set to 2:8, and the extruder temperature is adjusted to 210°C. After melting, the materials are filtered, and the materials extruded by the first twin-screw extruder are used as the A layer, and the materials extruded by the second twin-screw extruder are used as the B layer, and are extruded through a three-layer die; the melt extruded through the die is cooled at a temperature of 100°C, and is pulled at a pulling speed of 60m / min to obtain a three-layer composite casting sheet.

[0068] (3) The cast sheet was heat treated at 135°C for 18 h; then the heat treated cast sheet was firstly cold stretched longitudinally at 85°C with a stretching ratio of 1.2, then hot stretched longitudinally at 140°C with a stretching ratio of 2.0, and then heat set at 140°C for 4 min with a heat setting stretching ratio of 0.98, thereby obtaining a composite separator for a semi-solid battery.

[0069] Example 5

[0070] The difference from Example 1 is that the Zn-MOF material is calcined at 1200° C. for 3 h to obtain a Zn-MOF derived carbon material.

[0071] The composite separator for semi-solid batteries includes an ABA three-layer structure with a total thickness of 18μm.

[0072] Layer A: The thickness is 1.8 μm (the thickness is 10% of the total thickness), and the thicknesses of the upper and lower Layer A are the same; by mass percentage, the raw materials of Layer A are 90% PEO and 10% Zn-MOF-derived carbon material.

[0073] Layer B: The thickness is 14.4 μm (the thickness is 80% of the total thickness); the raw material of Layer B is a polypropylene material with a low melt index (0.8 - 1.0 g / 10min).

[0074] The preparation of the composite separator for the semi-solid battery includes the following steps:

[0075] (1) Zinc nitrate hexahydrate and 2-methylimidazole were added to a mixed solution of methanol and ethanol (volume ratio 1:1) at a molar ratio of 1:10, stirred well and left to stand for 30 min, then filtered by suction, washed with ethanol and water respectively, and dried and ground to obtain Zn-MOF material. In a nitrogen atmosphere, the Zn-MOF material was placed in a muffle furnace and heated at a rate of 12 °C / min to 1200 °C and calcined for 3 h to obtain Zn-MOF-derived carbon material.

[0076] (2) The raw materials of Layer A were proportionally fed into a mixing bin for mixing and then put into the first twin-screw extruder; the raw materials of Layer B were put into the second twin-screw extruder; the extrusion ratio of the first twin-screw extruder (including the upper and lower Layer A) to the second twin-screw extruder was set to 2:8, the temperature of the extruder was adjusted to 210 °C, melted and then filtered. The material extruded from the first twin-screw extruder was used as Layer A, and the material extruded from the second twin-screw extruder was used as Layer B, and they were extruded by in-die compound extrusion through a three-layer die head. The melt extruded from the die head was cooled at a temperature of 100 °C and drawn at a traction speed of 60 m / min to obtain a three-layer composite cast sheet.

[0077] (3) The cast sheet was heat-treated at a temperature of 135 °C for 18 h; immediately after that, the heat-treated cast sheet was first longitudinally cold-drawn at a temperature of 85 °C with a draw ratio of 1.2, then longitudinally hot-drawn at a temperature of 140 °C with a draw ratio of 2.0, and then heat-set at a temperature of 140 °C for 4 min with a heat-set draw ratio of 0.98 to obtain the composite separator for the semi-solid battery.

[0078] Example 6

[0079] The difference from Example 1 is that the extrusion ratio of the first twin-screw extruder (including the upper and lower Layer A) to the second twin-screw extruder is set to 3:7.

[0080] The composite separator for the semi-solid battery includes a three-layer ABA structure with a total thickness of 18 μm.

[0081] A layer: The thickness is 2.7 μm (15% of the total thickness), and the thickness of the upper and lower A layers is the same; in terms of mass percentage, the raw materials of the A layer are 90% PEO and 10% Zn-MOF-derived carbon material.

[0082] Layer B: thickness is 12.6 μm (thickness is 70% of the total thickness); the raw material of layer B is polypropylene material with low melt index (0.8-1.0 g / 10min).

[0083] The preparation of the composite diaphragm for the semi-solid battery comprises the following steps:

[0084] (1) Zinc nitrate hexahydrate and 2-methylimidazole were added to a mixture of methanol and ethanol (volume ratio of 1:1) in a molar ratio of 1:10, stirred thoroughly and allowed to stand for 30 minutes, then filtered, washed with ethanol and water, dried and ground to obtain Zn-MOF material. In a nitrogen atmosphere, the Zn-MOF material was placed in a muffle furnace, heated at a rate of 10°C / min, heated to 900°C and calcined for 4 hours to obtain a Zn-MOF-derived carbon material.

[0085] (2) The raw materials of layer A are put into a mixing silo in proportion for mixing, and then put into a first twin-screw extruder; the raw materials of layer B are put into a second twin-screw extruder; the extrusion volume ratio of the first twin-screw extruder (including the upper and lower A layers) and the second twin-screw extruder is set to 3:7, and the extruder temperature is adjusted to 210°C. After melting, the material is filtered, and the material extruded by the first twin-screw extruder is used as the A layer, and the material extruded by the second twin-screw extruder is used as the B layer, and is extruded through a three-layer die; the melt extruded through the die is cooled at a temperature of 100°C, and is pulled at a pulling speed of 60m / min to obtain a three-layer composite casting sheet.

[0086] (3) The cast sheet was heat treated at 135°C for 18 h; then the heat treated cast sheet was firstly cold stretched longitudinally at 85°C with a stretching ratio of 1.2, then hot stretched longitudinally at 140°C with a stretching ratio of 2.0, and then heat set at 140°C for 4 min with a heat setting stretching ratio of 0.98, thereby obtaining a composite separator for a semi-solid battery.

[0087] Comparative Example 1

[0088] The difference from Example 1 is that the raw material of layer A is only PEO.

[0089] The composite separator for semi-solid batteries includes an ABA three-layer structure with a total thickness of 18μm.

[0090] Layer A: The thickness is 1.8 μm (10% of the total thickness), and the thicknesses of the upper and lower Layer A are the same; by mass percentage, the raw material of Layer A is PEO.

[0091] Layer B: The thickness is 14.4 μm (80% of the total thickness); the raw material of Layer B is a polypropylene material with a low melt index (0.8 - 1.0 g / 10min).

[0092] The preparation of the composite separator for the semi-solid battery includes the following steps:

[0093] (1) Put the raw material of Layer A into the first twin-screw extruder; put the raw material of Layer B into the second twin-screw extruder; set the extrusion ratio of the first twin-screw extruder (including the upper and lower Layer A) and the second twin-screw extruder to 2:8, adjust the extruder temperature to 210 °C, and after melting, filter it. Take the material extruded from the first twin-screw extruder as Layer A, and the material extruded from the second twin-screw extruder as Layer B, and perform in-mold composite extrusion through a three-layer die head. The melt extruded from the die head is cooled at a temperature of 100 °C, and a three-layer composite cast sheet is obtained by pulling at a pulling speed of 60 m / min.

[0094] (3) Heat-treat the cast sheet at a temperature of 135 °C for 18 h; immediately longitudinally cold-draw the heat-treated cast sheet at a temperature of 85 °C with a draw ratio of 1.2, then longitudinally hot-draw it at a temperature of 140 °C with a draw ratio of 2.0, and then perform heat setting at a temperature of 140 °C for 4 min with a heat-setting draw ratio of 0.98 to obtain the composite separator for the semi-solid battery.

[0095] Comparative Example 2

[0096] The difference from Example 1 is that: 90% of PEO and 10% of Ni-MOF-derived carbon material are used as the raw material of Layer A.

[0097] The composite separator for the semi-solid battery includes a three-layer ABA structure with a total thickness of 18 μm.

[0098] Layer A: The thickness is 1.8 μm (10% of the total thickness), and the thicknesses of the upper and lower Layer A are the same; by mass percentage, the raw material of Layer A is 90% of PEO and 10% of Ni-MOF-derived carbon material.

[0099] Layer B: The thickness is 14.4 μm (80% of the total thickness); the raw material of Layer B is a polypropylene material with a low melt index (0.8 - 1.0 g / 10min).

[0100] The preparation of the composite separator for the semi-solid battery includes the following steps:

[0101] (1) Nickel nitrate hexahydrate and 2-methylimidazole were added to a mixed solution of methanol and ethanol (volume ratio 1:1) at a molar ratio of 1:10. After sufficient stirring, the mixture was allowed to stand for 30 min, then filtered by suction, washed with ethanol and water respectively, and dried and ground to obtain Ni-MOF material. Under a nitrogen atmosphere, the Ni-MOF material was placed in a muffle furnace and heated at a rate of 10 °C / min to 900 °C and calcined for 4 h to obtain Ni-MOF-derived carbon material.

[0102] (2) The raw materials of layer A were proportionally fed into a mixing bin for mixing and then put into the first twin-screw extruder; the raw materials of layer B were put into the second twin-screw extruder; the extrusion ratio of the first twin-screw extruder (including upper and lower layer A) to the second twin-screw extruder was set to 2:8, the temperature of the extruder was adjusted to 210 °C, and after melting, it was filtered. The material extruded from the first twin-screw extruder was used as layer A, and the material extruded from the second twin-screw extruder was used as layer B, and they were co-extruded through a three-layer die head in the die; the melt extruded from the die head was cooled at a temperature of 100 °C and drawn at a draw speed of 60 m / min to obtain a three-layer composite cast sheet.

[0103] (3) The cast sheet was heat-treated at a temperature of 135 °C for 18 h; immediately after that, the heat-treated cast sheet was first longitudinally cold-drawn at a temperature of 85 °C with a draw ratio of 1.2, then longitudinally hot-drawn at a temperature of 140 °C with a draw ratio of 2.0, and then heat-set at a temperature of 140 °C for 4 min with a heat-set draw ratio of 0.98 to obtain a composite separator for semi-solid batteries.

[0104] Comparative Example 3

[0105] The difference from Example 1 is that the raw materials of layer A used 90% PEO and 10% Co-MOF-derived carbon material.

[0106] The composite separator for semi-solid batteries includes an ABA three-layer structure with a total thickness of 18 μm.

[0107] Layer A: The thickness is 1.8 μm (10% of the total thickness), and the thicknesses of the upper and lower layer A are the same; by mass percentage, the raw materials of layer A are 90% PEO and 10% Co-MOF-derived carbon material.

[0108] Layer B: The thickness is 14.4 μm (80% of the total thickness); the raw materials of layer B are polypropylene materials with a low melt index (0.8 - 1.0 g / 10 min).

[0109] The preparation of the above-mentioned composite separator for semi-solid batteries includes the following steps:

[0110] (1) Cobalt nitrate hexahydrate and 2-methylimidazole were added to a mixture of methanol and ethanol (volume ratio of 1:1) in a molar ratio of 1:10, stirred thoroughly and allowed to stand for 30 minutes, then filtered, washed with ethanol and water, dried and ground to obtain Co-MOF material. In a nitrogen atmosphere, the Co-MOF material was placed in a muffle furnace, heated at a rate of 10°C / min, and heated to 900°C for 4 hours to obtain a Co-MOF-derived carbon material.

[0111] (2) The raw materials of layer A are put into a mixing silo in proportion for mixing, and then put into a first twin-screw extruder; the raw materials of layer B are put into a second twin-screw extruder; the extrusion volume ratio of the first twin-screw extruder (including the upper and lower A layers) and the second twin-screw extruder is set to 2:8, and the extruder temperature is adjusted to 210°C. After melting, the materials are filtered, and the materials extruded by the first twin-screw extruder are used as the A layer, and the materials extruded by the second twin-screw extruder are used as the B layer, and are extruded through a three-layer die; the melt extruded through the die is cooled at a temperature of 100°C, and is pulled at a pulling speed of 60m / min to obtain a three-layer composite casting sheet.

[0112] (3) The cast sheet was heat treated at 135°C for 18 h; then the heat treated cast sheet was firstly cold stretched longitudinally at 85°C with a stretching ratio of 1.2, then hot stretched longitudinally at 140°C with a stretching ratio of 2.0, and then heat set at 140°C for 4 min with a heat setting stretching ratio of 0.98, thereby obtaining a composite separator for a semi-solid battery.

[0113] Comparative Example 4

[0114] The difference from Example 1 is that the raw material of layer A uses 90% PEO and 10% Zn-MOF material.

[0115] The composite separator for semi-solid batteries includes an ABA three-layer structure with a total thickness of 18μm.

[0116] A layer: The thickness is 1.8 μm (10% of the total thickness), and the thickness of the upper and lower A layers is the same; in terms of mass percentage, the raw materials of the A layer are 90% PEO and 10% Zn-MOF material.

[0117] Layer B: thickness is 14.4 μm (80% of the total thickness); the raw material of layer B is polypropylene material with a low melt index (0.8-1.0 g / 10min).

[0118] The preparation of the composite diaphragm for the semi-solid battery comprises the following steps:

[0119] (1) Zinc nitrate hexahydrate and 2-methylimidazole were added to a mixed solution of methanol and ethanol (volume ratio 1:1) at a molar ratio of 1:10. After stirring well, it was left standing for 30 min, then filtered by suction, washed with ethanol and water respectively, and dried and ground to obtain the Zn-MOF material.

[0120] (2) The raw materials of layer A were proportionally fed into the mixing bin for mixing, and then put into the first twin-screw extruder; the raw materials of layer B were put into the second twin-screw extruder; the extrusion ratio of the first twin-screw extruder (including the upper and lower layer A) and the second twin-screw extruder was set to 2:8, the temperature of the extruder was adjusted to 210 °C, and after melting, it was filtered. The material extruded from the first twin-screw extruder was used as layer A, and the material extruded from the second twin-screw extruder was used as layer B, and it was extruded by in-mold compounding through a three-layer die; the melt extruded from the die was cooled at a temperature of 100 °C and drawn at a drawing speed of 60 m / min to obtain a three-layer composite cast sheet.

[0121] (3) The cast sheet was heat-treated at a temperature of 135 °C for 18 h; immediately after that, the heat-treated cast sheet was first longitudinally cold-drawn at a temperature of 85 °C with a draw ratio of 1.2, then longitudinally hot-drawn at a temperature of 140 °C with a draw ratio of 2.0, and then heat-set at a temperature of 140 °C for 4 min with a heat-set draw ratio of 0.98 to obtain a composite separator for semi-solid batteries.

[0122] Comparative Example 5

[0123] The difference from Example 1 is that the raw materials of layer A used 85% PEO, 5% Zn-MOF-derived carbon material, and 10% Zn-MOF material.

[0124] The composite separator for semi-solid batteries includes an ABA three-layer structure with a total thickness of 18 μm.

[0125] Layer A: The thickness is 1.8 μm (10% of the total thickness), and the thickness of the upper and lower layer A is the same; by mass percentage, the raw materials of layer A are 85% PEO, 5% Zn-MOF-derived carbon material, and 10% Zn-MOF material.

[0126] Layer B: The thickness is 14.4 μm (80% of the total thickness); the raw materials of layer B are polypropylene materials with a low melt index (0.8 - 1.0 g / 10 min).

[0127] The preparation of the above-mentioned composite separator for semi-solid batteries includes the following steps:

[0128] (1) Zinc nitrate hexahydrate and 2-methylimidazole were added to a mixed solution of methanol and ethanol (volume ratio 1:1) at a molar ratio of 1:10. After stirring well, the mixture was left standing for 30 min, then filtered by suction, washed with ethanol and water respectively, and dried and ground to obtain the Zn-MOF material. Under a nitrogen atmosphere, the Zn-MOF material was placed in a muffle furnace and heated at a rate of 10 °C / min to 900 °C and calcined for 4 h to obtain the Zn-MOF-derived carbon material.

[0129] (2) The raw materials of layer A were proportionally fed into a mixing bin for mixing and then put into the first twin-screw extruder; the raw materials of layer B were put into the second twin-screw extruder; the extrusion ratio of the first twin-screw extruder (including the upper and lower layer A) and the second twin-screw extruder was set to 2:8, the temperature of the extruder was adjusted to 210 °C, and after melting, it was filtered. The material extruded from the first twin-screw extruder was used as layer A, and the material extruded from the second twin-screw extruder was used as layer B, and they were co-extruded through a three-layer die head in the die; the melt extruded from the die head was cooled at a temperature of 100 °C and drawn at a draw speed of 60 m / min to obtain a three-layer composite cast sheet.

[0130] (3) The cast sheet was heat-treated at a temperature of 135 °C for 18 h; immediately afterwards, the heat-treated cast sheet was first longitudinally cold-drawn at a temperature of 85 °C with a draw ratio of 1.2, then longitudinally hot-drawn at a temperature of 140 °C with a draw ratio of 2.0, and then heat-set at a temperature of 140 °C for 4 min with a heat-set draw ratio of 0.98 to obtain a composite separator for a semi-solid battery.

[0131] The composite separators prepared in the above examples and comparative examples were cut into A4 size and various tests were carried out. The results are shown in Table 1.

[0132] The test items and methods are as follows:

[0133] (1) Average thickness: The thickness of different positions of the composite separator was measured using a micrometer and its average value was calculated.

[0134] (1) Tensile strength: The longitudinal and transverse tensile strengths of the composite separator were tested using a Xiqiang CTM universal testing machine. Five specimens were tested in each direction and their average value was calculated.

[0135] (2) Puncture strength: The puncture strength of the composite separator was tested using a Xiqiang CTM universal testing machine. Five specimens were tested and their average value was calculated.

[0136] (3) Air permeability: The air permeability of the composite separator was tested using an air permeability tester. Five samples were tested and their average value was calculated.

[0137] (4)Liquid absorption rate: The liquid absorption rate of the composite separator was tested by the weighing method. First, the mass of the composite separator was recorded after it was completely dried. Then, the completely dried composite separator was immersed in the electrolyte (prepared by dissolving lithium hexafluorophosphate LiPF6 in a mixed solvent composed of ethylene carbonate EC, dimethyl carbonate DMC, and ethyl methyl carbonate EMC with a volume ratio of 1:1:1) for 24 h. After wiping the electrolyte on the surface, the weight of the separator was recorded again. The difference between the two recorded weights was the liquid absorption rate of the composite separator. Five samples were tested and their average value was calculated.

[0138] (5)100-cycle battery capacity retention rate test: In an argon environment, the composite separator was placed between the lithium iron phosphate positive electrode plate and the lithium metal negative electrode plate, and then the electrolyte (prepared by dissolving lithium hexafluorophosphate LiPF6 in a mixed solvent composed of ethylene carbonate EC, dimethyl carbonate DMC, and ethyl methyl carbonate EMC with a volume ratio of 1:1:1) was added to assemble a CR2032 button battery. The capacity measured in the first test was recorded as the initial capacitance. After 100 cycles, it was recorded again, and the 100-cycle capacity retention rate of the battery was calculated.

[0139] Table 1

[0140]

[0141] As shown in Table 1, the data of Examples 1-3 show that increasing the proportion of the Zn-MOF-derived carbon material added to the composite separator can improve the capacity retention rate of the battery. However, due to the limitations of the internal materials of the battery, continuing to increase the addition amount of the Zn-MOF-derived carbon material will not result in a significant increase in the capacity retention rate of the battery, and the mechanical properties of the separator will be greatly affected. The data of Examples 1 and 5 show that increasing the calcination temperature of the Zn-MOF material, some carbon materials will collapse in structure due to calcination at high temperature for a long time, and the capacity retention rate will decrease. The data of Examples 1 and 6 show that reducing the thickness of the middle B layer of the composite separator will affect the mechanical properties of the separator because the polypropylene material plays a role in mechanical support. However, the performance data in Examples 1-6 are all better than those in Comparative Examples 1-5, indicating that the composite separator obtained within the scope defined in the present invention can achieve better performance effects.

[0142] In Comparative Example 1, the Zn-MOF-derived carbon material was not added, and the mechanical properties, wettability, capacity retention rate, and other properties of the obtained separator were all poor. Compared with Comparative Example 1, in Examples 1-5, due to the introduction of Zn-MOF materials or Zn-MOF-derived carbon materials, the wettability of the overall separator was improved, and the liquid absorption rate of the separator could be increased. Among them, the carbon skeleton structure obtained after calcining Zn-MOF would further improve the wettability due to the defects that occurred during the calcination process. In Comparative Examples 2-3, the derived carbon materials prepared using Ni-MOF and Co-MOF still had metal clusters, which could not, like the Zn-MOF material, achieve the vaporization and escape of Zn through high-temperature calcination. Therefore, their stability and wettability were inferior to those of the Zn-MOF-derived carbon material, and the battery capacity retention rate would also decrease.

[0143] Moreover, the data of Example 2 and Example 4 showed that by adding Zn-MOF materials to replace part of the Zn-MOF-derived carbon materials, the mechanical properties, liquid absorption rate, etc. of the separator would not decrease significantly. However, due to the disintegration problem of Zn-MOF materials during long-term charge and discharge, the battery capacity retention rate would decrease. However, by controlling the addition amount of Zn-MOF materials within a certain range, better performance effects than those of the comparative examples could still be obtained, indicating that Zn-MOF materials and Zn-MOF-derived carbon materials could achieve good synergistic effects at a certain ratio. In Comparative Example 4, since only Zn-MOF materials were added, the capacity retention rate decreased significantly. In Comparative Example 5, too much Zn-MOF material was added, which also led to a significant decrease in the capacity retention rate, but it was slightly higher than that of Comparative Example 4.

[0144] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made using the description of the present invention, or directly or indirectly applied in other related technical fields, shall be similarly included in the patent protection scope of the present invention.

Claims

1. Application of a composite diaphragm in a semi-solid battery, characterized in that: The diaphragm in the semi-solid battery is a composite diaphragm; the composite diaphragm includes an ABA three-layer structure obtained by co-extrusion of three layers; the raw material of layer B includes polypropylene; in terms of mass percentage, the raw material of layer A is 85-95% PEO, 0-5% Zn-MOF material and the remaining Zn-MOF derived carbon material; zinc nitrate hexahydrate and 2-methylimidazole in a molar ratio of 1:10-11 are added to a mixture of methanol and ethanol, stirred and allowed to stand, then filtered and dried to obtain the Zn-MOF material; the Zn-MOF derived carbon material is obtained by calcining the Zn-MOF material at 900-1200°C in an inert atmosphere for 3-6 hours.

2. The application according to claim 1, characterized in that: In the ABA three-layer structure, the thickness ratio of layer A, layer B and layer A is 10-20%: 60-80%: 10-20%, and the thickness of the upper and lower A layers is the same.

3. The use according to claim 1 or 2, characterized in that: The thickness of the composite membrane is 12-20 μm.

4. The use according to claim 1, characterized in that: The melt index of the polypropylene is 0.8-1.0 g / 10 min.

5. The use according to claim 1, characterized in that: The standing time is 30-50 min.

6. A method for preparing a composite diaphragm for use as claimed in any one of claims 1 to 5, characterized in that: The steps include: (1) In an inert atmosphere, calcining the Zn-MOF material at 900-1200°C for 3-6 hours to obtain a Zn-MOF-derived carbon material; (2) The raw materials of layer A and layer B are mixed in proportion, and then subjected to three-layer co-extrusion, cooling and pulling to obtain a cast sheet; (3) The cast sheet is subjected to heat treatment, longitudinal cold stretching, longitudinal hot stretching, and heat setting in sequence to obtain a composite separator for a semi-solid battery.

7. The method for preparing the composite diaphragm according to claim 6, characterized in that: The extrusion temperature of the three-layer co-extrusion is 200-240°C.

8. The method for preparing the composite diaphragm according to any one of claims 6 to 7, characterized in that: The cooling temperature is 80-100° C.; the pulling speed is 40-80 m / min.

9. The method for preparing the composite diaphragm according to any one of claims 6 to 7, characterized in that: The heat treatment temperature is 110-150° C. and the time is 10-30 hours.

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