CN116780104A - Safe soft package battery and preparation method thereof - Google Patents
Safe soft package battery and preparation method thereof Download PDFInfo
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- CN116780104A CN116780104A CN202310683899.0A CN202310683899A CN116780104A CN 116780104 A CN116780104 A CN 116780104A CN 202310683899 A CN202310683899 A CN 202310683899A CN 116780104 A CN116780104 A CN 116780104A
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical group [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 17
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- 229920000573 polyethylene Polymers 0.000 claims description 6
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- 239000011248 coating agent Substances 0.000 claims description 5
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- 238000007872 degassing Methods 0.000 claims description 4
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- 229910052751 metal Inorganic materials 0.000 claims description 4
- 239000002184 metal Substances 0.000 claims description 4
- 239000002002 slurry Substances 0.000 claims description 4
- 239000002033 PVDF binder Substances 0.000 claims description 3
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- DPXJVFZANSGRMM-UHFFFAOYSA-N acetic acid;2,3,4,5,6-pentahydroxyhexanal;sodium Chemical group [Na].CC(O)=O.OCC(O)C(O)C(O)C(O)C=O DPXJVFZANSGRMM-UHFFFAOYSA-N 0.000 claims description 3
- 239000001768 carboxy methyl cellulose Substances 0.000 claims description 3
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- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 abstract description 12
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- 238000013461 design Methods 0.000 abstract description 6
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Landscapes
- Secondary Cells (AREA)
- Sealing Battery Cases Or Jackets (AREA)
Abstract
The invention belongs to the technical field of lithium ion batteries, and relates to a safety design of a soft package battery and a preparation method thereof. The invention discloses a safe soft package battery, which comprises an aluminum-plastic film bag, electrolyte and a bare cell, wherein the bare cell immersed in the electrolyte is sealed in the aluminum-plastic film bag, the bare cell comprises a positive plate, a negative plate, a diaphragm and a tab, the diaphragm comprises a first diaphragm and a second diaphragm, the tab comprises a first tab, a second tab and a third tab, the first diaphragm is a bare diaphragm, and the second diaphragm is a multifunctional diaphragm consisting of a base film and a modified layer; the positive plate, the base film, the modified layer, the bare diaphragm and the negative plate are sequentially attached; the second lug is electrically connected with the positive plate, the first lug is electrically connected with the negative plate, and the third lug is electrically connected with the modified layer. The soft-package battery provided by the invention can predict the internal short circuit caused by lithium precipitation at the negative electrode side, and the method is simple, quick and accurate, so that the occurrence of thermal runaway is effectively avoided.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and relates to a safety design of a soft package battery and a preparation method thereof.
Background
Since lithium ion batteries were first commercialized in 1991, their energy density has been greatly developed. The increase in energy density is an ever-increasing pursuit, and higher energy density also means greater risk, which makes the battery safety problem more pronounced. In addition, the use of batteries in more demanding environments is also a broad pursuit, for example batteries with super fast charge properties, batteries that can operate efficiently at low temperature. The harsh working conditions easily lead to lithium precipitation at the negative electrode side, and precipitated lithium dendrites can puncture the separator to cause internal short circuits, thereby causing thermal runaway of the battery. Therefore, the severe service environment puts higher demands on the safety of the battery.
Improving the thermal stability of the separator is an effective means of enhancing the safety of the battery, and the separator is generally modified with an inorganic material such as boehmite, alumina, or the like (CN 114759312 a). The direct cause of thermal runaway in batteries is that the rate of heat generation is greater than the rate of heat dissipation, resulting in the heat building up and exceeding a safety threshold (typically 90 ℃). Therefore, improving the thermal conductivity of the separator is one of means for effectively suppressing thermal runaway, and the improvement of the thermal conductivity of the separator by conventionally used inorganic materials is limited. A separator having both high thermal stability and thermal conductivity is expected to further improve the ability of a battery to resist thermal runaway, thereby improving its safety.
Another effective safety measure is to provide an early warning of thermal runaway of the battery, and commonly used early warning signals include electrical signals, thermal signals, and mechanical signals. The early warning of thermal runaway by electrical or thermal signals is simple, fast, but is prone to false positives, whereas the use of mechanical signals requires complex calculations and is therefore also difficult to integrate into battery management systems (B.Xia, Y.Shang, T.Nguyen, C.Mi, journal of Power Sources,337 (2017) 1-10;Y.Zhao,P.Liu,Z.Wang,L.Zhang,J.Hong,Applied Energy,207 (2017) 354-362.). Therefore, the development of a simple, rapid and accurate early warning method is a key to the effective prevention of thermal runaway.
Disclosure of Invention
The invention aims to provide a safety design of a soft package battery and a preparation method thereof.
In order to solve the technical problems, the invention provides a safe soft package battery which comprises an aluminum plastic film bag, electrolyte and a bare cell; the bare cell immersed in the electrolyte is sealed in an aluminum plastic film bag, the bare cell comprises a positive plate, a negative plate, a diaphragm and a tab, the diaphragm comprises a first diaphragm and a second diaphragm, the tab comprises a first tab, a second tab and a third tab, the first diaphragm is a bare diaphragm, and the second diaphragm is a multifunctional diaphragm consisting of a base film (bare diaphragm) and a modified layer (conductive interlayer);
the positive plate, the base film, the modified layer, the bare diaphragm and the negative plate are sequentially attached; or the negative plate, the base film, the modified layer, the bare diaphragm and the positive plate are sequentially attached;
the second lug is electrically connected with the positive plate, the first lug is electrically connected with the negative plate, and the third lug is electrically connected with the modified layer.
Description: the second diaphragm is a multifunctional diaphragm modified by conductive materials; the modified layer of the second separator faces the first separator.
Improvement of the safety soft package battery as the invention: the bare cell assembly adopts a lamination or winding mode, wherein the lamination mode is single-layer lamination or multi-layer lamination, and the winding mode is multi-layer winding.
Further improvement of the safety soft pack battery as the present invention: the number of electrical connections of the modified layer of the second separator to the third ear is at least one (i.e., one or more), either in direct contact or via a metal foil.
Further improvement of the safety soft pack battery as the present invention: the second separator has in-plane electron conductivity; the second separator has both high thermal stability and high thermal conductivity.
Description: since the modified layer is a conductive material, the second separator has in-plane electron conductivity.
The invention also provides a preparation method of the safe soft package battery, which comprises the following steps:
1) Preparation of a multifunctional diaphragm:
the second diaphragm is a multifunctional diaphragm and comprises a base film and a modified layer, wherein the base film is a polyethylene porous film and a polypropylene porous film;
the conductive agent and the binder are mixed according to the proportion of 9+/-1: 1, adding a solvent into the obtained mixture for slurry mixing to obtain conductive slurry; the mass content of the mixture in the conductive paste (i.e., the solid content of the conductive paste) is 4 to 5% (preferably 4.4%);
coating conductive paste on a base film, and then drying (60-80 ℃) to form a modified layer with the thickness of 1-5 mu m on the base film; the size of the modified layer is the same as that of the base film;
the conductive agent is a carbon nano tube, and the binder is sodium carboxymethyl cellulose, styrene-butadiene rubber or polyvinylidene fluoride;
2) Cutting a diaphragm:
the size of the bare diaphragm is equal to that of the multifunctional diaphragm and is larger than that of the negative plate;
the bare diaphragm is a polyethylene porous film and a polypropylene porous film;
3) Preparing a pole piece:
the pole piece comprises a positive pole piece and a negative pole piece;
4) Cutting the pole piece:
the size of the positive plate is smaller than that of the negative plate;
5) Bare cell assembly:
the bare cell assembly adopts lamination or winding technology, wherein the basic unit of the bare cell is a positive plate, a multifunctional diaphragm, a bare diaphragm and a negative plate, or the basic unit of the bare cell is a positive plate, a bare diaphragm, a multifunctional diaphragm and a negative plate, and the modified layer of the multifunctional diaphragm faces the bare diaphragm;
the lamination mode is single-layer lamination or multi-layer lamination, and the winding mode is multi-layer winding;
6) Welding the electrode lugs:
the positive electrode plate is welded with the second electrode lug, the negative electrode plate is welded with the first electrode lug, and the third electrode lug is electrically connected with the modified layer of the multifunctional diaphragm in a direct contact or a contact manner through a metal foil;
and then carrying out conventional bagging and packaging, vacuum baking, liquid injection, degassing, packaging and standing.
The method comprises the following steps:
7) Bagging and packaging:
packaging the bare cell welded with the tab into an aluminum plastic film bag, and packaging the top edge and one side edge of the tab;
8) Vacuum baking:
baking the packaged battery cells under vacuum at 60-90 ℃ for 4-6 hours;
9) And (3) liquid injection:
injecting electrolyte into the baked battery cell, wherein the liquid injection amount is 0.5-10mL;
10 Degassing and packaging:
degassing the cell after liquid injection and packaging the other side edge;
11 Standing:
and (3) standing the packaged soft package battery at room temperature or high temperature, wherein the standing temperature is 20-80 ℃ and the standing time is 4-24h.
Compared with the prior art, the invention has the following beneficial effects:
1) The soft-package battery provided by the invention can predict the internal short circuit caused by lithium precipitation at the negative electrode side, and the method is simple, quick and accurate, so that the occurrence of thermal runaway is effectively avoided;
2) The soft package battery provided by the invention comprises the multifunctional diaphragm with high thermal stability and high thermal conductivity, and can effectively improve the thermal safety of the battery.
Drawings
The following describes the embodiments of the present invention in further detail with reference to the accompanying drawings.
Fig. 1 is a schematic structural view of a single-layered laminate pouch battery prepared in example 1;
FIG. 2 is a multifunctional separator prepared in example 1;
FIG. 3 is the voltage and current of the soft pack battery and the voltage of the modified layer in the overcharge test of example 1;
FIG. 4 is a differential scanning calorimetric curve of example 1;
FIG. 5 is a multifunctional separator prepared in example 2;
FIG. 6 is the voltage and current of the soft pack battery and the voltage of the modified layer in the overcharge test of example 2;
FIG. 7 is a differential scanning calorimetric curve of example 2;
FIG. 8 is a schematic view showing a part of the multi-layered laminate type soft pack battery prepared in example 3;
fig. 9 is a schematic structural view of a wound pouch battery prepared in example 4;
fig. 10 is a schematic structural view of a single-layered laminate pouch battery prepared in comparative example 1;
FIG. 11 is the voltage and current of the pouch cell and the voltage of the modified layer in the overcharge test of comparative example 1;
FIG. 12 is a differential scanning calorimetric curve of comparative example 1;
Detailed Description
The invention will be further described with reference to the following specific examples, but the scope of the invention is not limited thereto:
the substances used in the present invention can be obtained in commercially available forms, for example:
the polyethylene porous membrane is as follows: thickness is 12 μm and porosity is 41%; for example, a polyethylene porous membrane of MA-EN-SE-0C from Kodado company;
hydrophilic carbon nanotubes: diameter of 10nm, carbon nanotube content of 5%; for example, MA-EN-CO-0E0114 hydrophilic carbon nanotubes available from kodado company;
lipophilic carbon nanotubes: the diameter is 9nm, and the carbon nano tube contains 4 percent; for example, the MA-EN-CO-0B lipophilic carbon nano tube of Ke Loude company can be selected;
the positive plate is a ternary positive plate (a positive plate coated on one side); single-sided capacity 3.03mAh/cm 2 For example, can be selected fromTernary positive electrode sheet of SY3203 of Kolu company;
the positive plate is a ternary positive plate (a positive plate coated on two sides); single-sided capacity 3.03mAh/cm 2 For example, a ternary positive electrode sheet of SY3204 of Ke Liquide company can be selected;
the negative electrode plate is a graphite negative electrode plate (single-sided coating or double-sided coating), and the single-sided capacity is 3.44mAh/cm 2 In the case of a single-sided coated graphite negative electrode sheet, for example, a graphite negative electrode sheet of SM0204 from kodado company; in the case of a double-sided coated graphite negative electrode sheet, for example, the graphite negative electrode sheet of SM0205 of kodado company may be used.
Example 1, a single-layered laminate type soft pack battery of safety design, sequentially performed the following steps:
1) Preparation of a multifunctional diaphragm:
hydrophilic carbon nanotubes and polyvinylidene fluoride were mixed in a ratio of 9:1 as a mixture. Adding N-methyl pyrrolidone into the mixture, and uniformly stirring to obtain conductive paste with the mass content of 4.4% of the mixture, namely, the solid content of the conductive paste is 4.4%;
selecting a polyethylene porous membrane as a bare diaphragm;
the conductive paste was coated on a base film (bare separator was selected as the base film) with a wire rod of 47 μm (gap size) to form a wet film of a conductive separator having a thickness of 47 μm, and then transferred to an oven at 60 ℃ for drying for 1 hour to obtain a multifunctional separator composed of a base film (bare separator) and a modified layer (conductive separator having a thickness of about 2 μm). The morphology of the multifunctional diaphragm is shown in figure 2.
2) Cutting a diaphragm:
the bare membrane and the multifunctional membrane were cut to 53.2×45.7mm, respectively. That is, the bare membrane and the multifunctional membrane are identical in size.
3) Preparing a pole piece:
the positive plate is a ternary positive plate (a positive plate coated on one side), and the negative plate is a copper plate.
4) Cutting the pole piece:
the positive electrode sheet was cut to 49.5X42.0 mm, and the negative electrode sheet was cut to 51.0X43.5 mm.
5) Bare cell assembly:
the bare cell assembly adopts a single-layer lamination process, and the bare cells are sequentially laminated (attached) in the sequence of positive electrode plate-base film-modified layer-bare diaphragm-negative electrode plate, namely, the modified layer of the multifunctional diaphragm faces the bare diaphragm. The schematic diagram is shown in figure 1.
6) Welding the electrode lugs:
an aluminum tab (second tab) is welded on the positive electrode sheet of the bare cell, a nickel tab (first tab) is welded on the negative electrode sheet, a copper foil (thickness of 5 μm) with the thickness of 4.0 multiplied by 20.0mm is stuck on the modified layer of the multifunctional diaphragm, and then the copper foil and the other nickel tab (third tab) are welded together.
7) Bagging and top side sealing:
an aluminum plastic film bag with openings at the top edge and two sides is selected, and the size of the aluminum plastic film bag is larger than that of the bare cell; and (3) filling the bare cell welded with the tab obtained in the step (6) into an aluminum plastic film bag, wherein the end parts of the first tab, the second tab and the third tab are exposed out of the top edge of the aluminum plastic film bag. And packaging the top edge and any one side edge of the aluminum plastic film bag.
8) Vacuum baking:
baking the packaged battery cells for 4 hours in a vacuum environment at 85 ℃.
9) And (3) liquid injection:
injecting 0.5mL of electrolyte into the aluminum-plastic film bag provided with the baked battery cell;
the electrolyte is a known electrolyte, for example, LB-002 electrolyte of Duoduochi chemical company can be selected.
10 Side seal):
and packaging the other side edge of the aluminum plastic film bag.
11 Standing:
and standing the packaged battery for 24 hours at room temperature, so that the electrolyte fully infiltrates the battery cell.
12 Upper clamp
The stationary battery was fitted with a jig under a pressure of 0.4 MPa. That is, the jig is in contact with only the aluminum plastic film pouch, so that the internal contact of the battery is good.
Description: the steps 7) to 12) are all conventional techniques.
Experiment 1, overcharge test of single-layer laminated soft package battery:
1) Test line connection:
adopting 2 battery test channels, namely a battery test channel A and a battery test channel B;
the counter electrode and the reference electrode of the battery test channel A are connected with a first electrode lug, and the working electrode and the working sensing electrode are connected with a second electrode lug; the voltage of the soft package battery is obtained by the working sensing electrode of the test channel A;
the reference electrode of the battery test channel B is connected with the first electrode lug, and the working sensing electrode is connected with the third electrode lug; the counter electrode and the working electrode of the battery test channel B are in the air; the voltage of the modified layer of the multifunctional diaphragm is obtained by the working sensing electrode of the test channel B.
2) Overcharge test:
the battery was overcharged under conditions of 5C, 5V, while the voltage response of the modified layer was recorded.
The data recorded in the single-layered laminate type soft pack battery prepared in example 1 are shown in FIG. 3, V Cell Representing the voltage of the soft-packed battery, V o-CNT Representing the voltage of the modified layer of the multifunctional diaphragm, the abrupt change of the voltage of the modified layer towards 0 reflects that lithium dendrites penetrate through the bare diaphragm and form an internal short circuit with the conductive interlayer.
The bottom solid line of fig. 3 represents current;
the 3 arrows in fig. 3, left-hand and right-hand arrows represent the coordinates listed in the curve, and the down arrow indicates the location of the voltage dip.
From fig. 3, it can be known that: when V is o-CNT When the data of (a) suddenly drops, it can be determined that the negative electrode and the modified layer form an internal short circuit.
Experiment 2 the multifunctional separator of example 1 was taken for thermal performance testing:
1) Thermal stability test:
the multifunctional diaphragm is tested by using a differential scanning calorimeter, the heating rate is 3 ℃/min, and the protective gas is nitrogen.
2) Thermal conductivity testing:
and heating the multifunctional diaphragm by adopting an electric heating source, wherein the heating temperature is 100 ℃, the heat preservation time is 5min, and then detecting the temperature distribution of the diaphragm by utilizing an infrared imager.
The recorded data are shown in FIG. 4, with differential scanning calorimetric curves showing two peaks at 136.4 and 146.9℃with a total area of 224.9J/g; infrared imaging shows that the temperature distribution of the multifunctional diaphragm is uniform.
Example 2, a single-layered laminate type soft pack battery of safety design, sequentially performed the following steps:
1) Preparation of a multifunctional diaphragm:
combining lipophilic carbon nanotubes with sodium carboxymethylcellulose at 9:1 as a mixture. Adding deionized water into the obtained mixture, and uniformly stirring to obtain conductive paste with the mass content of 4.4% of the mixture, namely, the solid content of the conductive paste is 4.4%; the remainder being identical to step 1) of example 1. The morphology of the multifunctional diaphragm is shown in figure 5.
The subsequent assembly process (i.e., the subsequent step) of the pouch battery is identical to that of example 1.
The single-layered laminate type soft pack battery prepared in example 2 was subjected to overcharge test according to experiment 1, and the recorded data are shown in FIG. 6, V Cell Representing the voltage of the soft-packed battery, V a-CNT Representing the voltage of the modified layer of the multifunctional diaphragm, the abrupt change of the voltage of the modified layer towards 0 reflects that lithium dendrites penetrate through the bare diaphragm and form an internal short circuit with the conductive interlayer.
The multifunctional separator of example 2 was subjected to thermal performance testing according to experiment 2; the recorded data are shown in FIG. 7, wherein the differential scanning calorimetric curve shows two peaks at 137.1 and 146.3 ℃ with a total area of 206.5J/g; infrared imaging shows that the temperature distribution of the multifunctional diaphragm is uniform.
Example 3, a safely designed multi-layered laminate pouch battery, was subjected to the following steps in order:
1) Multifunctional separator preparation is equivalent to step 1) of example 1;
2) Cutting a diaphragm:
the bare membrane and the multifunctional membrane were cut to 53.2× 1005.4mm, respectively. The size of the bare diaphragm is consistent with that of the multifunctional diaphragm.
3) Preparing a pole piece:
the positive plate is a ternary positive plate (double-sided coating); the negative electrode plate is a graphite negative electrode plate, and the negative electrode plate is coated on one side or two sides.
4) Cutting the pole piece:
the cut sizes of the positive electrode sheet and the negative electrode sheet were the same as in example 1.
5) Bare cell assembly:
the bare cell assembly adopts a Z-type lamination process,
the base film, the modified layer and the bare diaphragm are combined to form a film component (namely, the bare diaphragm and the multifunctional diaphragm form the film component, the modified layer of the multifunctional diaphragm faces the bare diaphragm), the film component is folded in a Z-shaped mode, and the negative plate and the positive plate are sequentially and alternately arranged in the adjacent 2-layer film component. The number of the negative plates is 10, the negative plates at the upper end and the lower end are coated on one side, the coating layer faces the adjacent positive plates, the negative plates at the inner part are coated on two sides, and the number of the positive plates is 9, and the positive plates are coated on two sides.
Description: the bare cell takes a positive electrode plate, a bare diaphragm, a multifunctional diaphragm and a negative electrode plate as basic units. Or the bare cell takes the positive plate-multifunctional diaphragm-bare diaphragm-negative plate as a basic unit.
6) Welding the electrode lugs:
the positive electrode tab position (3/4 of the left edge of the battery) of the bare cell is folded and welded together, and then an aluminum tab (first tab) is welded; the tab position of the negative electrode tab is folded (1/4 of the left edge of the battery) and welded together, and then a nickel tab (second tab) is welded; the modified layer of the multifunctional diaphragm is stuck with copper foil with the thickness of 4.0 multiplied by 20.0mm (5 mu m) and welded with another nickel tab (third tab); namely, the third ear is positioned at 1/2 of the left edge of the battery; a schematic diagram thereof is shown in fig. 8.
Description: the tab welding is a conventional technique.
The following steps 7) to 12) are all conventional techniques, and are briefly described as follows:
7) Bagging and top side sealing:
and the bare cell welded with the electrode lugs is arranged in an aluminum plastic film bag, and the top edge and one side edge of the electrode lugs are packaged.
8) Vacuum baking:
baking the packaged battery cells for 6 hours in a vacuum environment at 85 ℃.
9) And (3) liquid injection:
3.0mL of electrolyte was injected into the baked cell under vacuum, and the cell was allowed to stand for 2 hours.
10 Side seal):
and packaging the other side edge of the aluminum plastic film bag with the air bag.
11 Standing:
and standing the packaged soft package battery at 70 ℃ for 6 hours.
12 Cut the air pocket):
the air bag of the battery is cut off and the sides are encapsulated.
Overcharge test of the resulting multi-layered laminate type pouch cell was referred to in experiment 1.
The results obtained were: the voltage of the modified layer tends to be abrupt toward 0 when lithium dendrites pierce through the bare separator and form an internal short with the conductive barrier layer.
Example 4, a wound pouch battery of safety design, followed in order by the following steps:
1) Multifunctional separator preparation was identical to example 1;
2) Cutting a diaphragm:
the bare membrane and the multifunctional membrane were cut to 93.2X 1751.8mm, respectively. The size of the bare diaphragm is consistent with that of the multifunctional diaphragm.
3) Preparing a pole piece:
the positive plate is a ternary positive plate, and the positive plate is coated on two sides; the negative electrode plate is a graphite negative electrode plate, and the negative electrode plate is coated on one side or two sides.
4) Cutting the pole piece:
the positive electrode sheet was cut to 89.5X 1451.8mm, and the negative electrode sheet was cut to 91.0X 1601.8mm.
5) Bare cell assembly:
the bare cell is assembled by adopting a winding process, the bare cell takes a positive plate, a bare diaphragm, a multifunctional diaphragm and a negative plate as basic units, a modified layer of the multifunctional diaphragm faces the bare diaphragm, a negative plate at the outermost layer is coated on one side, a coating layer faces the positive plate, a negative plate at the inner layer is coated on both sides, and both negative plates are coated on both sides.
6) Welding the electrode lugs:
an aluminum tab (a first tab) is welded on the tab position of the positive electrode tab of the bare cell, a nickel tab (a second tab) is welded on the tab position of the negative electrode tab, and a copper foil (with the thickness of 5 mu m) of 4.0 multiplied by 20.0mm is adhered to the modified layer of the multifunctional diaphragm and welded with the other nickel tab (the third tab). The schematic diagram is shown in fig. 9.
The following steps 7) to 12) are all conventional techniques, and are briefly described as follows:
7) Bagging and top side sealing:
and the bare cell welded with the electrode lugs is arranged in an aluminum plastic film bag, and the top edge and one side edge of the electrode lugs are packaged.
8) Vacuum baking:
baking the packaged battery cells for 6 hours in a vacuum environment at 85 ℃.
9) And (3) liquid injection:
10mL of electrolyte was injected into the baked cell under vacuum, and the cell was allowed to stand for 2 hours.
10 Side seal):
and packaging the other side edge of the aluminum plastic film bag with the air bag.
11 Standing:
and standing the packaged soft package battery at 70 ℃ for 6 hours.
12 Cut the air pocket):
the air bag of the battery is cut off and the sides are encapsulated.
The overcharge test and the like of the obtained wound-type soft-pack battery were referred to in experiment 1.
The results obtained were: the voltage of the modified layer tends to be abrupt toward 0 when lithium dendrites pierce through the bare separator and form an internal short with the conductive barrier layer.
Comparative example 1-1, relative to example 1, "multifunctional separator preparation" of step 1) of example 1 was omitted; the positive electrode sheet, the bare diaphragm and the negative electrode sheet are sequentially laminated to form a bare cell, the schematic structure is shown in fig. 10, and the rest is the same as in example 1.
The detection methods of comparative experiment 1 and comparative example 1-1 are as follows:
1) Test line connection:
the counter electrode and the reference electrode of a battery test channel are connected with a first electrode lug (connected with a negative electrode plate), and the working electrode and the working sensing electrode are connected with a second electrode lug (connected with a positive electrode plate).
2) Overcharge test:
the battery was overcharged at 5C, 5V.
The recorded data are as shown in FIG. 11, V Cell The voltage representing the soft pack battery cannot be used for early warning of internal short circuit because no multifunctional membrane exists, i.e. no detectable signal indicates whether the underlying bare membrane is pierced by lithium dendrites.
Comparative experiment 2 the bare diaphragm was subjected to thermal performance testing (thermal stability testing and thermal conductivity testing) in the manner described in experiment 2:
the recorded data are shown in FIG. 12, wherein the differential scanning calorimetric curve shows a peak at 136.4℃only, the total area of the peak being 218.7J/g; infrared imaging shows that the temperature distribution of the bare diaphragm is uneven and heat is concentrated around the spot heating source.
Comparison of fig. 4, 7 and 12 shows that: the multifunctional separator has better thermal stability than the bare separator.
Therefore, the comparative example 1-1 has a disadvantage in that heat cannot be timely emitted, resulting in a local temperature that is too high, thereby causing thermal runaway of the battery.
Comparative example 2, relative to example 3, the "multifunctional separator preparation" of step 1) of example 3 was omitted; the bare cell uses a positive electrode sheet-bare diaphragm-negative electrode sheet as a basic unit, and the rest is the same as example 3.
Overcharge test of the pouch cell obtained in comparative example 2 was conducted according to the method described in comparative experiment 1.
The results obtained were: since there is no multifunctional membrane, i.e., no detectable signal, indicating whether the underlying bare membrane is pierced by lithium dendrites, no early warning of an internal short is possible.
Comparative example 3, relative to example 4, "multifunctional separator preparation" of step 1) of example 4 was omitted; the bare cell uses a positive electrode sheet-bare diaphragm-negative electrode sheet as a basic unit, and the rest is the same as that of example 4.
Overcharge test of the pouch cell obtained in comparative example 3 was conducted according to the method described in comparative experiment 1.
The results obtained were: since there is no multifunctional membrane, i.e., no detectable signal, indicating whether the underlying bare membrane is pierced by lithium dendrites, no early warning of an internal short is possible.
Comprehensive knowledge can be obtained that the puncture of the bare diaphragm by the lithium dendrite can be rapidly and accurately detected by detecting the voltage mutation of the multifunctional diaphragm modified layer, so that the early warning is carried out for the internal short circuit of the soft-packaged battery, and the occurrence of thermal runaway is effectively prevented; compared with a bare diaphragm, the multifunctional diaphragm has better thermal stability and thermal conductivity, so that the thermal tolerance of the soft-packaged battery is improved, and the occurrence rate of thermal runaway is effectively reduced. The two aspects work together to provide double guarantee for the safe operation of the soft package battery.
Finally, it should also be noted that the above list is merely a few specific embodiments of the present invention. Obviously, the invention is not limited to the above embodiments, but many variations are possible. All modifications directly derived or suggested to one skilled in the art from the present disclosure should be considered as being within the scope of the present invention.
Claims (7)
1. The utility model provides a safe soft packet of battery, includes plastic-aluminum membrane bag, electrolyte and naked electric core, its characterized in that:
the bare cell immersed in the electrolyte is sealed in an aluminum plastic film bag, the bare cell comprises a positive plate, a negative plate, a diaphragm and a tab, the diaphragm comprises a first diaphragm and a second diaphragm, the tab comprises a first tab, a second tab and a third tab, the first diaphragm is a bare diaphragm, and the second diaphragm is a multifunctional diaphragm composed of a base film and a modified layer;
the positive plate, the base film, the modified layer, the bare diaphragm and the negative plate are sequentially attached; or the negative plate, the base film, the modified layer, the bare diaphragm and the positive plate are sequentially attached;
the second lug is electrically connected with the positive plate, the first lug is electrically connected with the negative plate, and the third lug is electrically connected with the modified layer.
2. The safe pouch cell as defined in claim 1, wherein: the bare cell assembly adopts a lamination or winding mode, wherein the lamination mode is single-layer lamination or multi-layer lamination, and the winding mode is multi-layer winding.
3. The safe pouch cell as defined in claim 1 or 2, wherein: the number of the modified layers of the second diaphragm and the third lug is at least one, and the electric connection mode is direct contact or contact through metal foil.
4. A safe pouch cell as defined in claim 3, wherein: the second separator has in-plane electron conductivity.
5. The safe pouch cell defined in claim 4, wherein: the second separator has both high thermal stability and high thermal conductivity.
6. The method for manufacturing a safe soft pack battery according to any one of claims 1 to 5, comprising the steps of:
1) Preparation of a multifunctional diaphragm:
the second diaphragm is a multifunctional diaphragm and comprises a base film and a modified layer, wherein the base film is a polyethylene porous film and a polypropylene porous film;
the conductive agent and the binder are mixed according to the proportion of 9+/-1: 1, adding a solvent into the obtained mixture for slurry mixing to obtain conductive slurry; the mass content of the mixture in the conductive paste is 4-5%;
coating conductive paste on a base film, and then drying, thereby forming a modified layer with a thickness of 1-5 mu m on the base film; the size of the modified layer is the same as that of the base film;
2) Cutting a diaphragm:
the size of the bare diaphragm is equal to that of the multifunctional diaphragm and is larger than that of the negative plate;
3) Preparing a pole piece:
the pole piece comprises a positive pole piece and a negative pole piece;
4) Cutting the pole piece:
the size of the positive plate is smaller than that of the negative plate;
5) Bare cell assembly:
the bare cell assembly adopts lamination or winding technology, wherein the basic unit of the bare cell is a positive plate, a multifunctional diaphragm, a bare diaphragm and a negative plate, or the basic unit of the bare cell is a positive plate, a bare diaphragm, a multifunctional diaphragm and a negative plate, and the modified layer of the multifunctional diaphragm faces the bare diaphragm;
the lamination mode is single-layer lamination or multi-layer lamination, and the winding mode is multi-layer winding;
6) Welding the electrode lugs:
the positive electrode plate is welded with the second electrode lug, the negative electrode plate is welded with the first electrode lug, and the third electrode lug is electrically connected with the modified layer of the multifunctional diaphragm in a direct contact or a contact manner through a metal foil;
and then bagging and packaging, vacuum baking, liquid injection, degassing, packaging and standing.
7. The method for manufacturing a safe soft pack battery according to claim 6, wherein:
the conductive agent is a carbon nano tube, and the binder is sodium carboxymethyl cellulose, styrene-butadiene rubber or polyvinylidene fluoride.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202310683899.0A CN116780104A (en) | 2023-06-10 | 2023-06-10 | Safe soft package battery and preparation method thereof |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202310683899.0A CN116780104A (en) | 2023-06-10 | 2023-06-10 | Safe soft package battery and preparation method thereof |
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| Publication Number | Publication Date |
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| CN116780104A true CN116780104A (en) | 2023-09-19 |
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| CN202310683899.0A Pending CN116780104A (en) | 2023-06-10 | 2023-06-10 | Safe soft package battery and preparation method thereof |
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| Country | Link |
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