Negative electrode binder, preparation method, lithium battery negative electrode and lithium battery

Abstract

The invention discloses a negative electrode binder, a preparation method, a lithium battery negative electrode and a lithium battery. The negative electrode binder is obtained by polymerizing organic alcohol amine and acrylic acid, and at least comprises the following molecular formula: # imgabs0 #; wherein R1, R2 and R3 are respectively and independently selected from hydrogen or C1-C3 hydroxyl groups; the organic alcohol amine is one of ethanol amine, diethanol amine, isopropanolamine and diisopropanolamine. Amido in the organic alcohol amine reacts with carboxyl in the acrylic acid to generate amido bonds, so that the flexibility and toughness of the negative electrode binder are improved; meanwhile, hydroxyl in the organic alcohol amine and hydroxyl alcohol groups on the silicon surface have higher affinity. Therefore, the bonding degree of the adhesive to the silicon surface under the electrolyte infiltration condition is further improved. Therefore, the organic alcohol amine and the propylene compound cooperate with each other, so that the negative electrode binder has excellent flexibility, toughness, binding power and stability.

Description

Technical Field

[0001] The present invention relates to a negative electrode binder, in particular to a negative electrode binder, a preparation method, a lithium battery negative electrode and a lithium battery. Background Art

[0002] Research shows that the adhesion of the binder material is the key to affecting the adhesion performance. If the adhesion is too weak, the active substances, carbon materials, etc. in the negative electrode sheet will fall off from the negative electrode sheet, resulting in a decline in battery performance or even serious safety accidents. In addition, the negative electrode material layer includes a silicon-based negative electrode material and a conductive agent. Adding a polyacrylic acid (PAA) - type negative electrode binder during the preparation process of the negative electrode material layer can solve the problem of expansion of the negative electrode material layer at low cost to a certain extent. Research shows that the swelling degree of the binder material in the electrolyte is the key to affecting the adhesion performance. If the swelling degree of the binder in the electrolyte is too large, the binder will be separated from the negative electrode material, resulting in a poor adhesion effect in the negative electrode material. Summary of the Invention

[0003] To solve the above problems, the present invention provides a negative electrode binder, a preparation method, a lithium battery negative electrode and a lithium battery.

[0004] The present invention provides the following technical solutions: A negative electrode binder is obtained by polymerizing an organic alkanolamine and acrylic acid, and at least includes the following molecular formula: ; wherein, R1, R2, and R3 are each independently selected from hydrogen or C1 - C3 hydroxy; C1 - C3 hydroxy is a hydroxy group containing 1 - 3 carbon atoms; The organic alkanolamine is one or more of ethanolamine, diethanolamine, isopropanolamine, and diisopropanolamine.

[0005] A preparation method of the above negative electrode binder is to uniformly mix 10 parts by mass of the organic alkanolamine, 0.1 - 2 parts by mass of an initiator, and 0.1 - 2 parts by mass of a reducing agent, and then drop them into a mixed solution composed of 5 - 30 parts by mass of acrylic acid and 50 - 300 parts by mass of water at a constant speed within 1 h for polymerization reaction to obtain the negative electrode binder; the temperature of the polymerization reaction is 60°C - 90°C, and the time is 1 h - 3 h.

[0006] Further, the initiator is ammonium persulfate.

[0007] Further, the reducing agent is sodium hypophosphite.

[0008] A lithium battery negative electrode includes a current collector and a negative electrode material layer attached to the surface of the current collector, and the negative electrode material layer is prepared from a negative electrode active material, a conductive agent, and the above negative electrode binder.

[0009] Further, the preparation steps of the negative electrode material layer are as follows: Mix 7 parts by mass of negative electrode active material and 1.5 parts by mass of conductive agent evenly by grinding, add them into 1.5 parts by mass of negative electrode binder, and stir magnetically at 550 rpm for 5 h to obtain an active material slurry; coat the active material slurry on the surface of the current collector and dry to form the negative electrode material layer.

[0010] For example, lay the cut copper foil flat on a glass plate, use a film coater (25μm) to coat the active material slurry on the surface of the copper foil current collector, then transfer it to a vacuum oven and dry at 80°C for 8 h to fully remove the excess moisture. Pass the dried electrode sheet through an automatic roller press, and punch the sheet with a punching machine to obtain a lithium battery negative electrode with a diameter of 1 cm.

[0011] A lithium battery includes the above-mentioned lithium battery negative electrode.

[0012] The beneficial effects of the present invention are as follows: (1) In the negative electrode binder provided by the present invention, the carboxyl group of acrylic acid in the acrylic compound endows the negative electrode binder with excellent adhesion. The amino group in the organic alkanolamine reacts with the carboxyl group in the acrylic acid to form an amide bond, which improves the flexibility and toughness of the negative electrode binder; at the same time, the hydroxyl group in the organic alkanolamine has a higher affinity with the hydroxyalcohol group on the silicon surface. Therefore, the adhesion degree of the binder to the silicon surface under the condition of electrolyte infiltration is further improved; thus, the organic alkanolamine and the acrylic compound cooperate with each other, making the negative electrode binder have excellent flexibility, toughness, adhesion and stability; (2) When this negative electrode binder is applied to prepare a lithium battery negative electrode, the negative electrode binder can well respond to the volume change of the active material, so as to well inhibit the swelling of the negative electrode material layer. In addition, the appropriate electrolyte swelling property of the negative electrode binder also makes there be appropriate gaps between the active materials, allowing electrons to smoothly pass through the negative electrode and be transmitted to the external current collector, and then enabling the lithium battery to complete discharge; (3) When applied to a lithium battery negative electrode, its volume is not likely to change with the charge and discharge of the lithium battery. Description of the Drawings

[0013] Figure 1 It is the infrared spectrogram of the negative electrode binders of Example 1 - Example 3 and Comparative Example 1; Figure 2 It is the cycle performance curve of the lithium battery negative electrodes of Example 1 and Comparative Example 1 at a constant capacity of 1500 mAh / g; Figure 3 It is the comparison chart of the 180° peel test results of the negative electrode binders of Example 1 - Example 3 and Comparative Example 1; Figure 4SEM comparison diagrams of the negative electrode binder of Example 1 and Comparative Example 1 before and after 100 cycles. Among them, a is the SEM image of the negative electrode binder of Comparative Example 1 before 100 cycles, b is the SEM image of the negative electrode binder of Comparative Example 1 after 100 cycles, c is the SEM image of the negative electrode binder of Example 1 before 100 cycles, and d is the SEM image of the negative electrode binder of Example 1 after 100 cycles. Detailed implementation manners

[0014] To further elaborate on the technical means and effects adopted by the present invention to achieve the intended invention purpose, the following combines the drawings and preferred embodiments to detail the specific implementation manners, structures, features, and their effects according to the present invention as follows.

[0015] A negative electrode binder, a preparation method, a negative electrode of a lithium battery, and a lithium battery. By introducing an organic amine substance into the binder, not only the affinity of the binder for silicon is improved, but also the swelling degree of the binder in the electrolyte can be controlled, thereby significantly enhancing the bonding strength. Applying this negative electrode binder to the preparation of the negative electrode of a lithium battery improves the structural stability of the electrode sheet and also significantly improves the electrochemical performance.

[0016] In the present invention, the negative electrode active material includes but is not limited to existing carbon-based compounds, silicon-based compounds, titanium-based compounds, alloy materials, and transition metal compounds; the carbon-based compounds are divided into easily graphitizable carbon (soft carbon), difficultly graphitizable carbon (hard carbon), and graphite; the silicon-based compound is a silicon negative electrode; the titanium-based compounds include titanium dioxide and titanates (such as lithium titanate, lithium zinc titanate, and lithium copper titanate, etc.); the alloy materials include Al, Sn, Mg, Ag, Sb, etc.; the transition metal compounds include transition metal oxides, transition metal sulfides, and transition metal phosphides. The transition metal oxides include MOx (M is Fe, Co, Ni, Cu, Zn, etc.), the transition metal sulfides mainly include copper sulfide, molybdenum sulfide, cobalt sulfide, and iron sulfide, etc., and the phosphides include nickel, cobalt, copper, iron, and aluminum phosphides; in the following examples, the negative electrode active material is uniformly a silicon negative electrode.

[0017] The following further illustrates the embodiments of the present invention through multiple examples.

[0018] Example 1 A preparation method of a negative electrode binder. Mix 10 g of ethanolamine, 0.1 g of ammonium persulfate, and 0.1 g of sodium hypophosphite evenly and then drop them into a mixed solution composed of 5 g of acrylic acid and 50 g of water at a constant speed within 1 h for a polymerization reaction to obtain the negative electrode binder; the temperature of the polymerization reaction is 60 °C and the time is 1 h.

[0019] Perform infrared analysis on the obtained negative electrode binder, and the results are as Figure 1 . Combine Figure 1With the raw materials, its structural formula can be determined to contain: ; Among them, R1, R2, and R3 are H, H, and CH2OH respectively; Using this negative electrode binder to prepare a negative electrode, specifically: Mix 7 g of silicon negative electrode and 1.5 g of conductive agent evenly by grinding, add them to 1.5 g of the negative electrode binder, and stir magnetically at 550 rpm for 5 h to obtain an active material slurry; Coat the active material slurry on the surface of the current collector and dry to form a negative electrode material layer.

[0020] A lithium battery negative electrode includes a current collector and a negative electrode material layer attached to the surface of the current collector. The negative electrode material layer is prepared from a negative electrode active material, a conductive agent, and the negative electrode binder as described above.

[0021] A lithium battery includes the above-mentioned lithium battery negative electrode.

[0022] Example 2 Preparation method of the negative electrode binder: Mix 10 g of diethanolamine, 0.7 g of ammonium persulfate, and 0.7 g of sodium hypophosphite evenly and then drop them into a mixed solution composed of 13 g of acrylic acid and 130 g of water at a constant speed within 1 h for polymerization reaction to obtain the negative electrode binder; The temperature of the polymerization reaction is 70 °C and the time is 1.7 h.

[0023] Perform infrared analysis on the obtained negative electrode binder, and the results are as Figure 1 . Combining Figure 1 With the raw materials, its structural formula can be determined to contain: ; Among them, R1, R2, and R3 are C2H5OH, H, and CH2OH respectively; Using this negative electrode binder to prepare a negative electrode, specifically: Mix 7 g of silicon negative electrode and 1.5 g of conductive agent evenly by grinding, add them to 1.5 g of the negative electrode binder, and stir magnetically at 550 rpm for 5 h to obtain an active material slurry; Coat the active material slurry on the surface of the current collector and dry to form a negative electrode material layer.

[0024] A lithium battery negative electrode includes a current collector and a negative electrode material layer attached to the surface of the current collector. The negative electrode material layer is prepared from a negative electrode active material, a conductive agent, and the negative electrode binder as described above.

[0025] A lithium battery includes the above-mentioned lithium battery negative electrode.

[0026] Example 3 Preparation method of negative electrode binder: Mix 10 g of isopropanolamine, 1.3 g of ammonium persulfate, and 1.3 g of sodium hypophosphite evenly, and then dropwise add them to a mixed solution composed of 21 g of acrylic acid and 210 g of water at a constant speed within 1 h to carry out a polymerization reaction to obtain the negative electrode binder; the temperature of the polymerization reaction is 80 °C and the time is 2.4 h.

[0027] Perform infrared analysis on the obtained negative electrode binder, and the results are as Figure 1 . Combining Figure 1 with the raw materials, it can be determined that its structural formula contains: ; wherein, R1, R2, and R3 are H, CH3, and CH2OH respectively; Use this negative electrode binder to prepare a negative electrode. Specifically: Mix 7 g of silicon negative electrode and 1.5 g of conductive agent evenly by grinding, add them to 1.5 g of the negative electrode binder, and stir magnetically at 550 rpm for 5 h to obtain an active material slurry; coat the active material slurry on the surface of the current collector and dry it to form a negative electrode material layer.

[0028] A lithium battery negative electrode includes a current collector and a negative electrode material layer attached to the surface of the current collector. The negative electrode material layer is prepared from a negative electrode active material, a conductive agent, and the negative electrode binder as described above.

[0029] A lithium battery includes the above-mentioned lithium battery negative electrode.

[0030] Example 4 Preparation method of negative electrode binder: Mix 10 g of diisopropanolamine, 2 g of ammonium persulfate, and 2 g of sodium hypophosphite evenly, and then dropwise add them to a mixed solution composed of 30 g of acrylic acid and 300 g of water at a constant speed within 1 h to carry out a polymerization reaction to obtain the negative electrode binder; the temperature of the polymerization reaction is 90 °C and the time is 3 h.

[0031] Its structural formula contains: ; wherein, R1, R2, and R3 are C3H7O, hydrogen, and C2H5O respectively; Use this negative electrode binder to prepare a negative electrode. Specifically: Mix 7 g of silicon negative electrode and 1.5 g of conductive agent evenly by grinding, add them to 1.5 g of the negative electrode binder, and stir magnetically at 550 rpm for 5 h to obtain an active material slurry; coat the active material slurry on the surface of the current collector and dry it to form a negative electrode material layer.

[0032] A lithium battery negative electrode includes a current collector and a negative electrode material layer attached to the surface of the current collector. The negative electrode material layer is prepared from a negative electrode active material, a conductive agent, and the negative electrode binder as described above.

[0033] A lithium battery includes the lithium battery negative electrode described above.

[0034] Comparative Example 1 The negative electrode binder uses an aqueous solution of polyacrylic acid with a concentration of 20 wt% (purchased from Alfa Aesar, average Mw = 240,000).

[0035] Such as Figure 1 In Examples 1 to 3, it is at 1632 cm -1 Corresponding to the stretching vibration of C=O in the -CONH- bond, the appearance of these peaks confirms the successful reaction of polyacrylic acid with organic alkanolamine. At the same time, the intensity of these peaks increases with the increase in the polarity of the organic alkanolamine, which also proves from the side that the organic alkanolamine is introduced into acrylic acid.

[0036] The lithium battery negative electrode prepared in Example 1 and the lithium battery silicon negative electrode prepared using an aqueous solution of polyacrylic acid with a concentration of 20 wt% (purchased from Alfa Aesar, average Mw = 240,000) (the preparation method is the same as that of Example 1) were tested. The test methods are as follows: The cycle performance was tested by cyclic voltammetry on the assembled battery using a Solartron 1470E electrochemical workstation. Test parameters: scanning rate is 0.1 mV / s, voltage range is 0.01~1.2 V vs. Li / Li + for 10 cycles.

[0037] Such as Figure 2 In Comparative Example 1, the capacity began to decay after 125 cycles, while Example 1 still had a relatively high capacity after 200 cycles. The improvement in cycle performance proves that the introduction of organic alkanolamine has a significant effect on the capacity retention of the negative electrode.

[0038] Peel test, the 180° peel test was carried out using a universal material testing machine, and the bonding performance of the binder was qualitatively analyzed by the magnitude of the peel force. The maximum load of the universal material testing machine is 500 N, and the test speed range is 0.0005~1000 mm / min -1 . Sample preparation: Cut the dried electrode sheet into strips about 5 cm long and about 2 cm wide, cut double-sided tape of the same shape and stick the electrode sheet tightly on the glass slide, then stick a 3M transparent tape with a width of 1.5 cm on the electrode sheet, and roll it 5 times with a 500 N weight on the transparent tape. Test parameters: test speed is 120 mm / min, preload force is 0.1 N. The bonding strength between the sheet and the copper foil determines the integrity of the electrode. The bonding performance of the binder in the dry state was obtained through the 180° peel test, and the results are as Figure 3As shown. Compared with Comparative Example 1, Examples 1 to 3 have higher peel strength. After the electrode sheet of Comparative Example 1 was peeled off, the electrode material on the surface layer was stuck off by the tape, while the electrode sheets of Examples 1 to 3 were well maintained, and Example 1 had the strongest bonding performance.

[0039] As Figure 4 , before cycling, the negative electrodes of Example 1 and Comparative Example 1 were both relatively flat. However, after 100 cycles, obvious cracking occurred in Comparative Example 1, but Example 1 could still remain relatively intact, proving that the introduction of organic alkanolamine significantly improved the bonding effect.

[0040] The above are only the preferred embodiments of the present invention and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the equivalent embodiments by using the disclosed technical content within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A negative electrode binder, characterized in that, It is obtained by polymerizing organic alkanolamine and acrylic acid, and at least includes the following molecular formula: ； Wherein, R1, R2, and R3 are each independently selected from hydrogen or C1-C3 hydroxyl groups; The organic alkanolamine is one of ethanolamine, diethanolamine, isopropanolamine, and diisopropanolamine.

2. The preparation method of the negative electrode binder according to claim 1, characterized in that, Mix 10 parts by mass of the organic alkanolamine, 0.1-2 parts by mass of the initiator, and 0.1-2 parts by mass of the reducing agent evenly, and then drop them into a mixed solution composed of 5-30 parts by mass of acrylic acid and 50-300 parts by mass of water at a constant speed within 1 h for polymerization reaction to obtain the negative electrode binder; the temperature of the polymerization reaction is 60°C-90°C, and the time is 1 h-3 h.

3. The preparation method according to claim 2, wherein, The initiator is ammonium persulfate.

4. The preparation method according to claim 2, characterized in that, The reducing agent is sodium hypophosphite.

5. A negative electrode of a lithium battery, characterized in that, It includes a current collector and a negative electrode material layer attached to the surface of the current collector, and the negative electrode material layer is prepared from a negative electrode active material, a conductive agent, and the negative electrode binder as described in claim 1.

6. The negative electrode of the lithium battery according to claim 5, characterized in that, The preparation steps of the negative electrode material layer are as follows: Mix and grind 7 parts by mass of the negative electrode active material and 1.5 parts by mass of the conductive agent evenly, add them to 1.5 parts by mass of the negative electrode binder, and stir magnetically at 550 rpm for 5 h to obtain the active material slurry; coat the active material slurry on the surface of the current collector and dry it to form the negative electrode material layer.

7. A lithium battery, characterized in that, It includes the negative electrode of the lithium battery as described in claim 5.

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