Miniature lithium primary battery and preparation method thereof

Abstract

The invention discloses a miniature lithium primary battery and a preparation method thereof, and belongs to the technical field of primary batteries. Long-strip-shaped positive and negative pole pieces formed by sequentially connecting n positive and negative pole unit pieces are produced through a special die cutting tool, then the positive and negative poles are stacked into the battery cell through a cross-shaped cross stacking method, the prepared battery cell has a laminated structure, and compared with a traditional miniature lithium primary battery with a pressing block type positive pole, the contact area of the positive and negative poles is increased; and the positive electrode coating mode enables the positive electrode material to be in better contact with the current collector, so that the capacity of the positive electrode active material is favorably exerted, and the capacity retention ratio is high during high-rate discharge. The miniature lithium primary battery produced by the invention has small volume, high-rate discharge capability and good low-temperature performance at the same time.

Description

Technical Field

[0001] The invention belongs to the technical field of primary batteries, and in particular relates to a miniature lithium primary battery and a preparation method thereof. Background Art

[0002] Primary batteries, especially lithium primary batteries, have the advantages of high energy density and long storage life, and are widely used in various military and civilian fields. In view of the increasing demand for miniaturized power sources, miniature lithium primary batteries are the preferred battery system to achieve small size and high energy. Miniature lithium primary batteries currently have many applications, such as pacemaker batteries, tire pressure monitoring batteries, fishing float batteries, small instrument batteries, etc. Miniature lithium primary batteries come in various forms, especially button batteries. In addition, there are also miniature cylindrical batteries, needle batteries, special-shaped batteries, etc.

[0003] In order to increase the energy of the battery in a small volume, the existing micro lithium primary batteries mostly adopt a pressed block positive electrode structure, that is, the components of the positive electrode are pressed into a fixed shape by a mold, and then dried, assembled, injected, aged and other steps to make a single battery with metal lithium as the negative electrode. However, while this type of pressed block positive electrode structure has a high energy density, the rate performance of the battery will be greatly reduced. This is usually manifested as the actual capacity is much smaller than the nominal capacity when discharging at a higher rate, and some are even less than 50%; at the same time, this type of pressed block structure also greatly affects the low temperature performance of the micro lithium primary battery. The low temperature performance of the pressed block micro lithium primary battery of the same system is much lower than that of the conventional laminated or wound battery. In order to solve this problem, some battery manufacturers start with improving the current collecting structure of the pressed block positive electrode and provide a current collecting skeleton for the positive electrode material block, such as adding a positive electrode material holder, adding a current collecting ring, adding a current collecting sheet, and burying a current collecting net in the material block. However, this method does not fundamentally solve the reasons for the poor rate performance and low temperature performance of the pressed block micro lithium primary battery. Summary of the invention

[0004] The present invention provides a miniature lithium primary battery and a preparation method thereof. The miniature lithium primary battery cell is manufactured by adopting a stacked-sheet structure. The miniature lithium primary battery produced by the cell has a small volume, a high-rate discharge capability and good low-temperature performance.

[0005] The technical solution adopted by the present invention is: a method for preparing a miniature lithium primary battery, comprising the following steps:

[0006] Step 1: Use a homogenizer to mix the positive electrode active material, the conductive agent, the binder, and the solvent, wherein the mass ratio of the positive electrode active material, the conductive agent, and the binder is (80-96):(10-2):(10-2), and the solid content is 20%-70%;

[0007] Step 2: Use a coating machine to evenly coat the mixed slurry on the aluminum foil current collector, with a coating amount c of 15-80 mg / cm 2 After coating, the roller is used for rolling operation, and the rolling thickness is t:

[0008]

[0009] Where t is the rolling thickness, μm; ρ is the positive electrode compaction density, g / cm 3 ;t 0 is the thickness of aluminum foil current collector, μm;

[0010] Step 3, drying the rolled positive electrode material strip, and using a positive electrode die-cutting tool to cut out a long strip of positive electrode sheet connected in sequence by n positive electrode unit sheets, leaving a section of current collecting aluminum foil at one end of the positive electrode sheet as a positive electrode tab, and connecting two adjacent positive electrode unit sheets by a connecting section smaller than the positive electrode unit sheet, and using a negative electrode die-cutting tool to cut metal lithium into a long strip of negative electrode sheet connected in sequence by n negative electrode unit sheets matching the positive electrode sheet, and connecting two adjacent negative electrode unit sheets by a connecting section smaller than the negative electrode unit sheet;

[0011] Step 4: Start with the first negative electrode unit sheet at one end of the negative electrode, cross-overlap with the first positive electrode unit sheet at the non-ear end of the positive electrode, fold the negative electrode and positive electrode units in sequence, and add a separator between the positive and negative electrode units; fold in sequence until the negative electrode units are all folded into the battery cell, and only the positive electrode ear of the positive electrode unit sheet is left outside, the positive electrode ear is the positive electrode lead-out terminal, and one end is the first negative electrode unit sheet at the beginning of the stacking, and the negative electrode unit sheet is the negative electrode lead-out terminal;

[0012] Step 5, assembling the above-mentioned battery cell in a battery case, with the negative electrode lead end facing the negative electrode case, and a current collector pre-welded in the negative electrode case, and the positive electrode lead end facing the positive electrode case, and the current collector aluminum foil acting as the current collector, without the need for additional welding of the current collector;

[0013] Step six, injecting the lithium primary battery electrolyte into the assembled battery, and sealing the battery using a micro lithium primary battery sealing mold.

[0014] The positive electrode active material is manganese dioxide or carbon fluoride, the conductive agent is one of conductive carbon black, carbon fiber, carbon nanotube, and graphene, the binder is polyvinylidene fluoride PVDF or polytetrafluoroethylene PTFE, and the solvent is one of water, N-methyl-2-pyrrolidone NMP, N,N-dimethylacetamide DMAC, and dimethyl sulfoxide (DMSO).

[0015] The thickness of the aluminum foil current collector is t 0 8-20μm.

[0016] The diaphragm is made of PE, PP, non-woven fabric, and has a thickness of t 29-30μm.

[0017] The surface of the diaphragm is coated with a ceramic coating.

[0018] The miniature lithium primary battery is prepared by the above preparation method.

[0019] The present invention has the following advantages and positive effects:

[0020] 1. The present invention uses a special die-cutting tool to produce long strips of positive and negative electrode sheets connected in sequence by n positive and negative electrode unit sheets, and then stacks the positive and negative electrodes into battery cells through a "cross" cross stacking method. The prepared battery cells have a stacking-like structure. Compared with the traditional pressed block positive electrode, the contact area of ​​the positive and negative electrodes is increased. At the same time, the positive electrode coating method enables better contact between the positive electrode material and the current collector, which is beneficial to the use of the capacity of the positive electrode active material. At the same time, it has a high rate discharge capability and a high capacity retention rate.

[0021] 2. The present invention has simple operation steps. Except for the special die-cutting tool, the equipment used is simple, universal and easy to prepare.

[0022] 3. The laminated structure introduced in the present invention has a wide range of applications. By adjusting the size of the positive and negative electrode die cutting tools, it can adapt to the production of miniature lithium primary batteries of various dimensions, especially thin button batteries. The miniature lithium primary battery produced by this method has good rate performance and low temperature performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the positive electrode sheet of the present invention.

[0024] Figure 2 Schematic diagram of the negative electrode sheet of the present invention.

[0025] Figure 3 It is a schematic diagram of the "cross"-shaped cross laminations of the present invention.

[0026] Figure 4 Schematic diagram of a battery cell of the present invention.

[0027] Figure 5 It is an assembly schematic diagram of the present invention.

[0028] Figure 6 Normal temperature discharge curve.

[0029] Figure 7 Low temperature discharge curve.

[0030] In the figure: 1 positive electrode sheet, 2 negative electrode sheet, 3 separator, 4 current collecting aluminum foil, 5 battery cell, 6 current collecting sheet, 7 negative electrode shell, 8 positive electrode shell. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation methods described herein are only used to explain the present invention and are not used to limit the present invention.

[0032] A method for preparing a miniature lithium primary battery of the present invention comprises the following steps:

[0033] Step 1: Use a homogenizer to mix the positive electrode active material, the conductive agent, the binder, and the solvent, wherein the mass ratio of the positive electrode active material, the conductive agent, and the binder is (80-96):(10-2):(10-2), and the solid content is 20%-70%;

[0034] Step 2: Use a coating machine to evenly coat the mixed slurry on the aluminum foil current collector, with a coating amount c of 15-80 mg / cm 2 After coating, the roller is used for rolling operation, and the rolling thickness is t:

[0035]

[0036] Where t is the rolling thickness, μm; ρ is the positive electrode compaction density, g / cm 3 ;t 0 is the thickness of aluminum foil current collector, μm;

[0037] Step 3, drying the rolled positive electrode material strip, and using a positive electrode die-cutting tool to cut out a long strip of positive electrode sheet connected in sequence by n positive electrode unit sheets, leaving a section of current collecting aluminum foil at one end of the positive electrode sheet as a positive electrode tab, and connecting two adjacent positive electrode unit sheets by a connecting section smaller than the positive electrode unit sheet, and using a negative electrode die-cutting tool to cut metal lithium into a long strip of negative electrode sheet connected in sequence by n negative electrode unit sheets matching the positive electrode sheet, and connecting two adjacent negative electrode unit sheets by a connecting section smaller than the negative electrode unit sheet;

[0038] Step 4: Start with the first negative electrode unit sheet at one end of the negative electrode, cross-overlap with the first positive electrode unit sheet at the non-ear end of the positive electrode, fold the negative electrode and positive electrode units in sequence, and add a separator between the positive and negative electrode units; fold in sequence until the negative electrode units are all folded into the battery cell, and only the positive electrode ear of the positive electrode unit sheet is left outside, the positive electrode ear is the positive electrode lead-out terminal, and one end is the first negative electrode unit sheet at the beginning of the stacking, and the negative electrode unit sheet is the negative electrode lead-out terminal;

[0039] Step 5, assembling the above-mentioned battery cell in a battery case, with the negative electrode lead end facing the negative electrode case, and a current collector pre-welded in the negative electrode case, and the positive electrode lead end facing the positive electrode case, and the current collector aluminum foil acting as the current collector, without the need for additional welding of the current collector;

[0040] Step six, injecting the lithium primary battery electrolyte into the assembled battery, and sealing the battery using a micro lithium primary battery sealing mold.

[0041] The positive electrode active material is manganese dioxide or carbon fluoride, the conductive agent is one of conductive carbon black, carbon fiber, carbon nanotube, and graphene, the binder is polyvinylidene fluoride PVDF or polytetrafluoroethylene PTFE, and the solvent is one of water, N-methyl-2-pyrrolidone NMP, N,N-dimethylacetamide DMAC, and dimethyl sulfoxide (DMSO).

[0042] The thickness of the aluminum foil current collector is t 0 8-20μm.

[0043] The diaphragm is made of PE, PP, non-woven fabric, and has a thickness of t 2 9-30μm.

[0044] The surface of the diaphragm is coated with a ceramic coating.

[0045] The miniature lithium primary battery is prepared by the above preparation method.

[0046] In order to further disclose the content, features and effects of the present invention, the following examples are given to explain in detail:

[0047] Low temperature CR2032 mini lithium primary battery

[0048] Step 1: Use a homogenizer to mix manganese dioxide, conductive carbon black, polytetrafluoroethylene emulsion and water. The mass ratio of positive electrode active material, conductive agent and binder is 82:9:9, and the solid content is 30%.

[0049] Step 2: Use a coating machine to coat the mixed slurry on the aluminum foil current collector, with a coating amount of c = 55 mg / cm 2 After coating, the coating was rolled by a roller, and the rolling thickness t (μm) was calculated by the following formula: where ρ is the positive electrode compaction density, 2.45 g / cm 3 ;t 0 is the thickness of the aluminum foil current collector, 12μm.

[0050]

[0051] Step 3: Dry the rolled positive electrode strip and use the positive electrode die-cutting tool to cut out Figure 1 The positive electrode sheet 1 shown in FIG. At the same time, the negative electrode die cutting tool is used to cut the metal lithium into the following Figure 2 The negative electrode sheet 2 is shown.

[0052] The number of positive electrode sheets k is calculated as follows: 1 is the thickness of the battery cell, t is the thickness of the positive electrode, t 2is the diaphragm thickness, t 负 is the thickness of the negative electrode lithium sheet, T is the required thickness of the battery after assembly (the thickness of the positive and negative electrode shells after assembly), T 负 is the thickness of the negative electrode shell, T 正 is the thickness of the positive electrode shell, T 片 is the thickness of the negative electrode current collector. In this embodiment, T = 3.2 mm, T 正 =T 负 =0.25mm, T 片 =0.1mm, t 负 =0.15mm, t 2 =0.024mm. The result is rounded to an integer.

[0053]

[0054] t 1 ≤TT 负 -T 正 -T 片

[0055] Step 4: Place the die-cut positive and negative electrodes Figure 3 The stacking is performed by the "cross" method shown in the figure. First, the first "lantern"-shaped unit at one end of the negative electrode is started, and it is cross-overlaid with the tail end (non-ear end) of the positive electrode. Note that a separator 3 is added between the positive and negative electrodes as insulation; then, the negative and positive "lantern"-shaped units are folded in turn, and a separator is added between the positive and negative electrodes; fold in turn until all the negative "lantern"-shaped units are folded into the battery cell, and only the positive ear 4 of the positive electrode is left outside, as shown in FIG. Figure 4 At this time, one end of the battery cell is the positive electrode ear 4, which is the positive electrode lead-out terminal; the other end is the first negative electrode "lantern"-shaped unit at the beginning of stacking, which is the negative electrode lead-out terminal.

[0056] Step 5: Assemble the above-mentioned battery cell in a CR2032 battery shell, wherein the negative electrode lead end in the battery cell 5 faces the negative electrode shell 7, and the negative electrode current collector 6 is pre-welded in the negative electrode shell 7, while the positive electrode lead end faces the positive electrode shell 8, and the current collecting aluminum foil 4 acts as the current collecting sheet, and no additional current collecting sheet needs to be welded.

[0057] Step 6: Inject the low-temperature lithium primary battery electrolyte into the assembled battery, and then use a dedicated CR2032 type sealing machine to seal the battery.

[0058] Experimental results:

[0059] The miniature lithium primary battery manufactured by the above embodiment has good rate performance and low temperature performance.

[0060] The above low-temperature CR2032 micro lithium primary battery was discharged to 1.5V at 20mA and 100mA at room temperature, and the battery capacity was 122mAh and 114mAh respectively, and the capacity retention rate at high rate was 93%. Figure 6 Normal temperature discharge curve.

[0061] After the above low-temperature CR2032 micro lithium primary battery was stored at -55℃ for 2h and discharged at 2mA constant current to 1.5V, the battery capacity was 89.5mAh, and the capacity retention rate at -55℃ was 73%. Figure 7 Low temperature discharge curve.

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a miniature lithium primary battery, characterized in that: The following steps are involved: Step 1: Use a homogenizer to mix the positive electrode active material, the conductive agent, the binder, and the solvent, wherein the mass ratio of the positive electrode active material, the conductive agent, and the binder is (80-96):(10-2):(10-2), and the solid content is 20%-70%; Step 2: Use a coating machine to evenly coat the mixed slurry on the aluminum foil current collector, with a coating amount c of 15-80 mg / cm 2 After coating, the roller is used for rolling operation, and the rolling thickness is t: Where t is the rolling thickness, μm; ρ is the positive electrode compaction density, g / cm 3 ; t0 is the thickness of aluminum foil current collector, μm; Step 3, drying the rolled positive electrode material strip, and using a positive electrode die-cutting tool to cut out a long strip of positive electrode sheet connected in sequence by n positive electrode unit sheets, leaving a section of current collecting aluminum foil at one end of the positive electrode sheet as a positive electrode tab, and connecting two adjacent positive electrode unit sheets by a connecting section smaller than the positive electrode unit sheet, and using a negative electrode die-cutting tool to cut metal lithium into a long strip of negative electrode sheet connected in sequence by n negative electrode unit sheets matching the positive electrode sheet, and connecting two adjacent negative electrode unit sheets by a connecting section smaller than the negative electrode unit sheet; Step 4: Start with the first negative electrode unit sheet at one end of the negative electrode, cross-overlap with the first positive electrode unit sheet at the non-ear end of the positive electrode, fold the negative electrode and positive electrode units in sequence, and add a separator between the positive and negative electrode units; fold in sequence until the negative electrode units are all folded into the battery cell, and only the positive electrode ear of the positive electrode unit sheet is left outside, the positive electrode ear is the positive electrode lead-out terminal, and one end is the first negative electrode unit sheet at the beginning of the stacking, and the negative electrode unit sheet is the negative electrode lead-out terminal; Step 5, assembling the above-mentioned battery cell in a battery case, with the negative electrode lead end facing the negative electrode case, and a current collector pre-welded in the negative electrode case, and the positive electrode lead end facing the positive electrode case, and the current collector aluminum foil acting as the current collector, without the need for additional welding of the current collector; Step six, injecting the lithium primary battery electrolyte into the assembled battery, and sealing the battery using a micro lithium primary battery sealing mold.

2. The method for preparing a miniature lithium primary battery according to claim 1, characterized in that: The positive electrode active material is manganese dioxide or carbon fluoride, the conductive agent is one of conductive carbon black, carbon fiber, carbon nanotube, and graphene, the binder is polyvinylidene fluoride PVDF or polytetrafluoroethylene PTFE, and the solvent is one of water, N-methyl-2-pyrrolidone NMP, N,N-dimethylacetamide DMAC, and dimethyl sulfoxide (DMSO).

3. The method for preparing a miniature lithium primary battery according to claim 1, characterized in that: The thickness t0 of the aluminum foil current collector is 8-20 μm.

4. The method for preparing a miniature lithium primary battery according to claim 1, characterized in that: The diaphragm is made of PE, PP, or non-woven fabric, and has a thickness t2 of 9-30 μm.

5. The method for preparing a miniature lithium primary battery according to claim 1, characterized in that: The surface of the diaphragm is coated with a ceramic coating.

6. A miniature lithium primary battery prepared by the preparation method according to any one of claims 1 to 5.

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