A coating composition, and electrochemical devices and electronic devices comprising the same

Abstract

The application provides a coating composition, an electrochemical device and an electronic device comprising the same, the coating composition comprising a modified melamine salt and a binder. The endothermic temperature of the modified melamine salt characterized on a differential scanning calorimetry curve is lower than that of an unmodified melamine salt, and the difference is Δt, 5℃≤Δt≤100℃. Through the above setting, the electrochemical device has good high-temperature storage performance and mechanical safety performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemistry, in particular to a coating composition, an electrochemical device and an electronic device comprising the same. BACKGROUND

[0002] Electrochemical devices (such as lithium ion batteries) have the advantages of high energy storage density, high open circuit voltage, low self-discharge rate, long cycle life, good safety, etc., and are widely used in various fields such as electric energy storage, mobile electronic devices, electric vehicles and aerospace. With the rapid development of mobile electronic devices and electric vehicles, the market has increasingly high requirements for the energy density and safety performance of electrochemical devices. However, electrochemical devices are prone to explosion when subjected to heat exposure, penetration, collision, impact, etc., and the safety performance needs to be improved.

[0003] The prior art usually adopts a coating layer including non-active materials such as aluminum oxide, boehmite, barium sulfate, magnesium oxide on the surface of the separator, which can reduce the possibility of overheating and explosion of the electrochemical device. However, when the above non-active materials are used in the coating layer, the separator has no interaction with the transport of lithium ions and electrons in the positive electrode sheet, resulting in poor stability of the electrochemical device, which further affects the high-temperature storage performance and mechanical safety performance of the electrochemical device. At present, the market demand for electrochemical devices with good high-temperature storage performance and mechanical safety performance is increasing. SUMMARY

[0004] The purpose of the present application is to provide a coating composition, an electrochemical device and an electronic device comprising the same, to improve the high-temperature storage performance and mechanical safety performance of the electrochemical device.

[0005] It should be noted that the present application uses lithium ion batteries as an example of electrochemical devices to explain the present application, but the electrochemical devices of the present application are not limited to lithium ion batteries. The specific technical solutions are as follows:

[0006] The first aspect of the present application provides a coating composition, which comprises a modified melamine salt and a binder, wherein the endothermic temperature of the modified melamine salt characterized on the differential scanning calorimetry (DSC) curve is lower than that of the unmodified melamine salt, and the difference is Δt, 5℃≤Δt≤100℃. Compared with the unmodified melamine salt, the modified melamine salt has a lower endothermic temperature, which can regulate the thermal decomposition temperature. By using the modified melamine salt in the coating composition and regulating Δt within the range of the present application, the high-temperature storage performance and mechanical safety performance of the electrochemical device can be improved.

[0007] In an embodiment of the present application, 15℃≤Δt≤60℃. By regulating the value of Δt within the above range, the high-temperature storage performance and mechanical safety performance of the electrochemical device can be further improved.

[0008] In an embodiment of the present application, the solubility of the modified melamine salt in the test electrolyte is s1, and s1<0.1 g / g. By regulating the solubility s1 of the modified melamine salt in the test electrolyte within the above range, the dissolved modified melamine salt in the test electrolyte can be reduced, the stability of the coating composition can be improved, and thus the high-temperature storage performance and mechanical safety performance of the electrochemical device can be improved.

[0009] In an embodiment of the present application, s1≤0.02 g / g. By regulating the solubility s1 of the modified melamine salt in the test electrolyte within the above range, the dissolved modified melamine salt in the test electrolyte can be further reduced, the stability of the coating composition can be improved, and thus the high-temperature storage performance and mechanical safety performance of the electrochemical device can be further improved.

[0010] In an embodiment of the present application, the thermal weight loss mass residue rate of the modified melamine salt characterized on a thermogravimetric method (TG) curve is w, and 1%≤w≤35%. By regulating the thermal weight loss mass residue rate w of the modified melamine salt within the above range, the thermal stability of the modified melamine salt can be improved, and the possibility of high-temperature decomposition of the modified melamine salt can be reduced, and thus the high-temperature storage performance and mechanical safety performance of the electrochemical device can be improved.

[0011] In an embodiment of the present application, 4.56%≤w≤33%. By regulating the thermal weight loss mass residue rate w of the modified melamine salt within the above range, the high-temperature storage performance and mechanical safety performance of the electrochemical device can be further improved.

[0012] In an embodiment of the present application, the particle size of the modified melamine salt is Dv50, and 0.1 μm≤Dv50≤3 μm. By regulating the particle size Dv50 of the modified melamine salt within the above range, the particle size of the coating composition can be moderate, the thickness and uniformity of the coating can be improved, and thus the high-temperature storage performance and mechanical safety performance of the electrochemical device can be improved.

[0013] In an embodiment of the present application, 0.3 μm≤Dv50≤1.5 μm. By regulating the value of the particle size Dv50 of the modified melamine salt within the above range, the thickness and uniformity of the coating can be further improved, and thus the high-temperature storage performance and mechanical safety performance of the electrochemical device can be further improved.

[0014] In one embodiment of the present application, the mass percentage of the modified melamine salt is a, 50%≤a≤99% based on the mass of the coating composition. By regulating the mass percentage of the modified melamine salt a in the above range, the modified melamine salt in the coating composition has a suitable mass, which can reduce heat generation when problems such as overheating or impact occur, thereby improving the high-temperature storage performance and mechanical safety performance of the electrochemical device.

[0015] In one embodiment of the present application, 70%≤a≤95%. By regulating the mass percentage of the modified melamine salt a in the above range, the modified melamine salt in the coating composition has a suitable mass, which further limits the movement of lithium ions and electrons in the positive electrode sheet when problems such as overheating or impact occur, makes it difficult for current to flow, and reduces heat generation, thereby further improving the high-temperature storage performance and mechanical safety performance of the electrochemical device.

[0016] In one embodiment of the present application, the binder includes at least one of polyacrylic acid, polyacrylate, polyvinylidene fluoride, styrene butadiene rubber, sodium carboxymethyl cellulose, polyvinyl alcohol, polyimide, or aluminum hydroxide sol. By regulating the type of binder in the above range, the high-temperature storage performance and mechanical safety performance of the electrochemical device can be improved.

[0017] In one embodiment of the present application, the modified melamine salt is obtained by introducing a molecular modifier in the reaction of melamine with an inorganic acid or an organic acid, the molecular modifier containing a plurality of hydroxyl groups or a plurality of amino groups. By regulating the preparation method of the modified melamine salt within the scope of the present application, the modified melamine salt has a lower endothermic temperature compared to the unmodified melamine salt, thereby improving the high-temperature storage performance and mechanical safety performance of the electrochemical device.

[0018] In one embodiment of the present application, the molecular modifier includes a small molecule compound polymerized polyhydroxy high molecular polymer, the polyhydroxy high molecular polymer including at least one of polyvinyl alcohol, polyethylene glycol, or polymeric polyol. By regulating the type of molecular modifier in the above range, the high-temperature storage performance and mechanical safety performance of the electrochemical device can be improved.

[0019] In one embodiment of the present application, the molecular modifier includes a polyhydroxy compound or a polyamino compound. The polyhydroxy compound includes at least one of ethylene glycol, propylene glycol, glycerol, butanediol, hexanediol, pentaerythritol, ethylenediaminetetraacetic acid, trimethylol ethane, xylitol, or sorbitol. The polyamino compound includes at least one of ethylenediamine or hexamethylenetetramine. By regulating the type of molecular modifier in the above range, the high-temperature storage performance and mechanical safety performance of the electrochemical device can be improved.

[0020] In an embodiment of the present application, the inorganic acid comprises at least one of phosphoric acid, pyrophosphoric acid or boric acid, and the organic acid comprises at least one of cyanuric acid, phthalic acid, oxalic acid, phytic acid or 2-carboxyethyl phenyl phosphinic acid. By regulating the kind of inorganic acid or organic acid in the above range during the molecular modification process, the high-temperature storage performance and mechanical safety performance of the electrochemical device can be improved.

[0021] In an embodiment of the present application, the mass percentage content of the molecular modifier is b, 0.1%≤b≤15.0%, based on the total mass of the modified melamine salt. By regulating the value of the mass percentage content b of the molecular modifier in the above range, the molecular modifier has a suitable amount, the molecular modifier reaction can be complete, the residual molecular modifier is reduced, the possibility of the residual molecular modifier dissolving in the electrolyte is reduced, and thus the high-temperature storage performance and mechanical safety performance of the electrochemical device are further improved.

[0022] In an embodiment of the present application, 0.5%≤b≤5.0%. By regulating the value of the mass percentage content b of the molecular modifier in the above range, the molecular modifier reaction can be further complete, the residual molecular modifier is further reduced, the possibility of the residual molecular modifier dissolving in the electrolyte is reduced, and thus the high-temperature storage performance and mechanical safety performance of the electrochemical device are further improved.

[0023] In an embodiment of the present application, the absolute value of the pH difference between the modified melamine salt and the binder is m, 0≤m≤5.0. By regulating the absolute value m of the pH difference between the modified melamine salt and the binder in the above range, the pH of the binder and the modified melamine salt can be similar, and thus the high-temperature storage performance and mechanical safety performance of the electrochemical device are improved.

[0024] In an embodiment of the present application, 0≤m≤2.5. By regulating the absolute value m of the pH difference between the modified melamine salt and the binder in the above range, the high-temperature storage performance and mechanical safety performance of the electrochemical device are further improved.

[0025] The second aspect of the present application provides an electrochemical device comprising the coating composition in any of the foregoing embodiments. Therefore, the electrochemical device has good high-temperature storage performance and mechanical safety performance.

[0026] In an embodiment of the present application, the electrochemical device comprises a positive electrode sheet and a separator, wherein the coating composition is arranged on the surface of the separator facing the positive electrode sheet and / or at least one surface of the positive electrode sheet.

[0027] The third aspect of the present application provides an electronic device comprising the electrochemical device in any of the foregoing embodiments. Therefore, the electronic device has good high-temperature storage performance and mechanical safety performance.

[0028] The present application provides a coating composition, an electrochemical device and an electronic device comprising the same, the coating composition comprising a modified melamine salt and a binder, wherein the endothermic temperature of the modified melamine salt characterized on a DSC curve is lower than that of the unmodified melamine acid salt, and the difference is Δt, 5℃≤Δt≤100℃. The modified melamine salt has a lower endothermic temperature than the unmodified melamine salt, which can regulate the thermal decomposition temperature. By using the modified melamine salt in the coating composition and regulating Δt within the range of the present application, the high-temperature storage performance and mechanical safety performance of the electrochemical device can be improved.

[0029] Of course, implementing any product or method of the present application does not necessarily require achieving all the advantages described above at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other embodiments can also be obtained by those skilled in the art based on these drawings.

[0031] Figure 1 DSC curve of the modified melamine cyanurate in Example 1-2 of the present application;

[0032] Figure 2 DSC curve of the unmodified melamine cyanurate in Comparative Example 2 of the present application;

[0033] Figure 3 TG curve of the modified melamine cyanurate in Example 1-2 of the present application;

[0034] Figure 4 TG curve of the unmodified melamine cyanurate in Comparative Example 2 of the present application;

[0035] Figure 5 Scanning electron microscope photograph of the unmodified melamine cyanurate in Comparative Example 2 of the present application;

[0036] Figure 6 Scanning electron microscope photograph of the modified melamine cyanurate in Example 1-2 of the present application;

[0037] Figure 7 Scanning electron microscope photograph of the modified melamine cyanurate in Example 1-4 of the present application. DETAILED DESCRIPTION

[0038] The technical solutions in the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present application are within the scope of protection of the present application.

[0039] It should be noted that in the specific embodiments of the present application, the present application is explained by taking lithium-ion batteries as examples of electrochemical devices, but the electrochemical devices of the present application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0040] The first aspect of the present application provides a coating composition, which comprises a modified melamine salt and a binder, wherein the endothermic temperature of the modified melamine salt characterized on a DSC curve is lower than that of the unmodified melamine acid salt, and the difference is Δt, 5℃≤Δt≤100℃.

[0041] Exemplarily, Δt can be 5℃, 10℃, 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, or a range composed of any two of the above. When Δt<5℃, the difference in endothermic temperature is too small to reflect the performance difference between the modified melamine salt and the unmodified melamine salt; when Δt>100℃, the difference in endothermic temperature is too large, and the thermal stability of the modified melamine salt is poor, which causes decomposition or side reactions of the secondary battery in high-temperature (≥85℃) storage and other working environments, thereby affecting the high-temperature storage performance of the electrochemical device.

[0042] The inventors have found through research that when melamine salt is used in a coating composition, it can better limit the movement of lithium ions and electrons in the positive electrode sheet when the electrochemical device is subjected to heat exposure, penetration, collision, impact, etc., thereby making it difficult for current to flow, better inhibiting overheating and explosion of the electrochemical device, and having less impact on the normal working performance of the electrochemical device. On this basis, the inventors have made molecular modifications to the melamine salt in the coating composition. The endothermic temperature of the modified melamine salt characterized on a DSC curve is lower than that of the unmodified melamine salt, and the difference Δt satisfies 5℃≤Δt≤100℃. Compared with the unmodified melamine salt, the modified melamine salt has a lower endothermic temperature and can regulate the thermal decomposition temperature, thereby improving the high-temperature storage performance and mechanical safety performance of the electrochemical device.

[0043] The kind of modified melamine salt is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the modified melamine salt includes, but is not limited to, at least one of modified melamine phosphate, modified melamine cyanurate or modified melamine phthalate. It should be noted that "Δt" in the present application refers to the difference between the endothermic temperature of the same kind of melamine salt after modification and the endothermic temperature of the unmodified melamine salt. Exemplarily, in some embodiments, Δt refers to the difference between the endothermic temperature of the modified melamine phosphate and the endothermic temperature of the unmodified melamine phosphate.

[0044] In an embodiment of the present application, 15℃≤Δt≤60℃. Exemplarily, Δt can be 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃ or a range consisting of any two of the above values. By adjusting the value of Δt within the above range, the modified melamine salt can have better high-temperature storage performance and mechanical safety performance.

[0045] The adjustment method of Δt is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the value of Δt can be adjusted by changing the kind and / or mass percentage of the molecular modifier introduced during the synthesis of the modified melamine salt, or by introducing the molecular modifier in different stages of the synthesis of the modified melamine salt. Generally, the kind and / or mass percentage of the molecular modifier is different, Δt is different. For example, as the mass percentage of the molecular modifier increases, Δt increases.

[0046] In an embodiment of the present application, the solubility of the modified melamine salt in the test electrolyte is s1, and s1<0.1g / g. Exemplarily, the value of s1 can be 0.01g / g, 0.02g / g, 0.03g / g, 0.04g / g, 0.05g / g, 0.06g / g, 0.07g / g, 0.08g / g, 0.09g / g or a range consisting of any two of the above values. By adjusting the solubility s1 of the modified melamine salt in the test electrolyte within the above range, the dissolved modified melamine salt in the test electrolyte can be reduced, the stability of the coating composition can be improved, and thus the high-temperature storage performance and mechanical safety performance of the electrochemical device can be improved.

[0047] In the present application, the preparation method of the test electrolyte can include but is not limited to the following steps: mixing vinyl carbonate, propylene carbonate (PC) and diethyl carbonate (DEC) in a mass ratio of (15% to 25%):(25% to 35%):(55% to 65%) as a base solvent, mixing lithium salt LiPF6, carboxylic acid ester and fluoroethylene carbonate into the base solvent, stirring uniformly to obtain the test electrolyte. Among them, the mass percentage of lithium salt LiPF6 based on the mass of the test electrolyte can be 10% to 20%, the mass percentage of carboxylic acid ester and fluoroethylene carbonate can be 2% to 15% respectively, and the balance is the base solvent. The above-mentioned carboxylic acid ester includes but is not limited to at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone or capro lactone.

[0048] In an embodiment of the present application, the solubility of the modified melamine salt in the test electrolyte is s1, s1≤0.02g / g. Illustratively, the value of s1 can be 0.001g / g, 0.005g / g, 0.01g / g, 0.015g / g, 0.02g / g or a range composed of any two of the above values. By adjusting the solubility s1 of the modified melamine salt in the test electrolyte within the above range, the dissolved modified melamine salt in the test electrolyte is further reduced, the stability of the coating composition is improved, and the high-temperature storage performance and mechanical safety performance of the electrochemical device are further improved.

[0049] The present application does not have special restrictions on the adjustment method of the solubility of the modified melamine salt in the test electrolyte, as long as the purpose of the present application can be achieved. For example, it can be achieved by adjusting at least one of the reaction temperature, the reaction time or the cleaning and drying process in the synthesis process of the modified melamine salt.

[0050] In an embodiment of the present application, the modified melamine salt has a thermal weight loss mass residue rate w characterized by a thermogravimetric curve of 1% to 35%. Illustratively, the value of w can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, or a range between any two of the aforementioned values. The unmodified melamine salt will decompose and sublimate at a temperature greater than or equal to 250°C, and the modified melamine salt will carbonize and remain on the positive electrode sheet and / or the separator after being treated at a temperature greater than or equal to 250°C. By adjusting the thermal weight loss mass residue rate w of the modified melamine salt within the aforementioned range, the thermal response onset temperature and response rate of the modified melamine salt can be improved, so that when the electrochemical device generates heat rapidly, the modified melamine salt decomposes upon heating, absorbs heat to reduce the temperature, generates gas to dilute active oxygen, and reduces the likelihood of thermal runaway of the electrochemical device. At the same time, the product of the carbonized modified melamine salt can maintain the coating structure and reduce the likelihood of further contact between the positive electrode sheet and the negative electrode sheet to cause a short circuit. Thus, the high-temperature storage performance and mechanical safety performance of the electrochemical device are improved.

[0051] In an embodiment of the present application, 4.56%≤w≤33%. Illustratively, the value of w can be 4.56%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, or a range between any two of the aforementioned values. By adjusting the thermal weight loss mass residue rate w of the modified melamine salt within the aforementioned range, the thermal stability of the modified melamine salt can be further improved, thereby further improving the high-temperature storage performance and mechanical safety performance of the electrochemical device.

[0052] The present application does not have a particular limitation on the manner of adjusting the thermal weight loss mass residue rate w of the modified melamine salt, as long as the purpose of the present application can be achieved. For example, it can be achieved by changing at least one of the type or mass percentage content of the molecular modifier introduced during the synthesis of the modified melamine salt. Generally, the type and / or mass percentage content of the molecular modifier is different, and w is different.

[0053] In one embodiment of the present application, the particle size of the modified melamine salt is Dv50, 0.1 μm≤Dv50≤3.0 μm. Illustratively, the value of Dv50 can be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3.0 μm, or a range between any two of the aforementioned values. By adjusting the particle size Dv50 of the modified melamine salt within the aforementioned range, the particle size of the coating composition can be moderate, and the thickness and uniformity of the coating formed by the coating composition can be improved, thereby improving the high-temperature storage performance and mechanical safety performance of the electrochemical device.

[0054] In one embodiment of the present application, 0.3 μm≤Dv50≤1.5 μm. Illustratively, Dv50 can be 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, or a range between any two of the aforementioned values. By adjusting the value of the particle size Dv50 of the modified melamine salt within the aforementioned range, the thickness and uniformity of the coating formed by the coating composition can be further improved, thereby further improving the high-temperature storage performance and mechanical safety performance of the electrochemical device.

[0055] The present application does not have a particular limitation on the method of adjusting the particle size Dv50 of the modified melamine salt, as long as the purpose of the present application can be achieved. For example, the adjustment can be achieved by sieving or crushing.

[0056] In the present application, the particle size Dv50 of the modified melamine salt refers to the particle size at which the cumulative volume of the modified melamine salt particles reaches 50% from the small particle size side in the particle size distribution on a volume basis.

[0057] In one embodiment of the present application, the mass percentage of the modified melamine salt in the coating composition is a, and 50%≤a≤99%. Illustratively, a can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, or a range between any two of the aforementioned values. By adjusting the mass percentage of the modified melamine salt to be within the aforementioned range, the modified melamine salt in the coating composition can have a suitable mass, and the movement of lithium ions and electrons in the positive electrode sheet can be better limited when problems such as overheating or impact occur. In this way, the current flow can be difficult, and the effect of reducing heat generation can be achieved, thereby improving the high-temperature storage performance and mechanical safety performance of the electrochemical device.

[0058] In one embodiment of the present application, 70%≤a≤95%. Illustratively, a can be 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, or a range between any two of the aforementioned values. By adjusting the mass percentage of the modified melamine salt to be within the range of the present application, the modified melamine salt in the coating composition can have a suitable mass, and the movement of lithium ions and electrons in the positive electrode sheet can be further limited when problems such as overheating or impact occur, making the current flow difficult, and the effect of reducing heat generation can be achieved, thereby further improving the high-temperature storage performance and mechanical safety performance of the electrochemical device.

[0059] In one embodiment of the present application, the binder includes at least one of polyacrylic acid, polyacrylate, polyvinylidene fluoride, styrene butadiene rubber, sodium carboxymethyl cellulose, polyvinyl alcohol, polyimide, or aluminum hydroxide sol. By adjusting the type of binder to be within the range of the present application, the adhesion between the coating composition and the positive current collector can be improved, the degree of peeling of the coating composition and the positive current collector during cycling can be reduced, the interface contact resistance during cycling can be improved, and the high-temperature storage performance and mechanical safety performance of the electrochemical device can be improved.

[0060] The mass percentage of the binder in the coating composition is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the mass percentage of the binder can be 1% to 10% based on the mass of the coating composition.

[0061] In one embodiment of the present application, the coating composition further comprises a ceramic compound. The kind of the ceramic compound is not particularly limited in the present application as long as the object of the present application can be achieved. For example, the ceramic compound can include at least one of inorganic fast ion conductor, magnesium hydroxide, aluminum hydroxide, silicon dioxide, aluminum oxide, or boehmite. Among them, the inorganic fast ion conductor can include at least one of lithium titanium aluminum phosphate (Li 1+a Al a Ti 2-a (PO4)3, 0.1≤a≤0.5, abbreviated as LATP), lithium lanthanum titanium oxide (Li 3b La (2 / 3-b) TiO3, 0.03≤b≤0.167, abbreviated as LLTO), or lithium lanthanum zirconium oxide (Li7La3Zr2O 12 , abbreviated as LLZO). The kind of the ceramic compound is not particularly limited in the present application as long as the object of the present application can be achieved. For example, the mass percentage content of the ceramic compound is 0% to 50% based on the mass of the coating composition.

[0062] In one embodiment of the present application, the coating composition further comprises a wetting agent. The kind of the wetting agent is not particularly limited in the present application, and a conventional wetting agent known in the art can be used as long as the object of the present application can be achieved. The content of the wetting agent is not particularly limited in the present application as long as the object of the present application can be achieved. For example, the mass percentage content of the wetting agent is 0% to 2% based on the mass of the coating composition.

[0063] In one embodiment of the present application, the modified melamine salt is obtained by introducing a molecular modifier containing a plurality of hydroxyl groups or a plurality of amino groups in the process of reacting melamine with inorganic acid or organic acid. It should be noted that the "plurality" of the above-mentioned refers to 2 or more hydroxyl groups or amino groups. The number of hydroxyl groups and amino groups in the molecular modifier is not particularly limited in the present application as long as the object of the present application can be achieved. For example, the number of hydroxyl or amino functional groups can be 2 to 4. By introducing the molecular modifier in the process of hydrogen bonding self-assembly of melamine with inorganic acid or organic acid, the molecular modifier participates in the hydrogen bonding self-assembly process of melamine salt, destroys its planar regularity at the supramolecular level, interferes with the formation of uniform large planar hydrogen bonding network, and thus reduces the melting temperature. The preparation method of the modified melamine salt is within the scope of the present application, which can make the modified melamine salt have a heat absorption temperature difference within the scope of the present application compared with the unmodified melamine salt, thereby improving the high-temperature storage performance and mechanical safety performance of the electrochemical device.

[0064] The method for preparing the coating composition is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, in some embodiments, the method for preparing the coating composition comprises, but is not limited to, the following steps: (1) preparation of modified melamine salt: obtained by introducing a molecular modifier during the reaction of melamine with inorganic or organic acid. (2) preparation of coating composition: in a dispersion tank, the above-mentioned modified melamine salt, binder and ceramic compound are added, a solvent is added, and the mixture is uniformly dispersed to obtain the coating composition. The type of solvent in the above-mentioned step (2) is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the solvent includes, but is not limited to, N-methyl pyrrolidone (NMP) or deionized water.

[0065] In an embodiment of the present application, the molecular modifier includes a small molecule compound, a polyhydroxy high molecular polymer, and the polyhydroxy high molecular polymer includes at least one of polyvinyl alcohol (HO(CHCHO) n H), polyethylene glycol (HO(CH2CH2O) n H), or a polymerized polyol. The polyvinyl alcohol has a degree of polymerization n, which is divided into ultrahigh degree of polymerization (molecular weight 250,000 to 300,000), high degree of polymerization (molecular weight 170,000 to 220,000), medium degree of polymerization (molecular weight 120,000 to 150,000), and low degree of polymerization (molecular weight 25,000 to 35,000). The relative molecular mass of the polyethylene glycol is 200 to 6000, which can be used as a fusion promoter. The type of polymerized polyol is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the polymerized polyol can be at least one of polypropylene glycol (H(C3H6O) n OH) having a molecular weight of 400 to 2000 or glycerol homopolymer (HO(CH2OHCHCH2O) n H) having a molecular weight of 200 to 1500. By adjusting the type of molecular modifier within the above-mentioned range, the modified melamine salt can have different endothermic temperatures, thereby improving the high-temperature storage performance and mechanical safety performance of the electrochemical device.

[0066] In an embodiment of the present application, the molecular modifier includes a polyhydroxy compound or a polyamino compound. The polyhydroxy compound includes at least one of ethylene glycol, propylene glycol, glycerol, butanediol, hexanediol, pentaerythritol, ethylenediaminetetraacetic acid, trimethylol ethane, xylitol or sorbitol. The polyamino compound includes at least one of ethylenediamine or hexamethylenetetramine. By adjusting the type of molecular modifier within the above-mentioned range, the modified melamine salt can have different endothermic temperatures, thereby improving the high-temperature storage performance and mechanical safety performance of the electrochemical device.

[0067] In one embodiment of the present application, the inorganic acid comprises at least one of phosphoric acid, pyrophosphoric acid or boric acid, and the organic acid comprises at least one of cyanuric acid, phthalic acid, oxalic acid, phytic acid or 2-carboxyethyl phenyl phosphinic acid. By regulating the type of inorganic acid or organic acid in the above range during the molecular modification process, the modified melamine salt can have different endothermic temperatures, thereby improving the high-temperature storage performance and mechanical safety performance of the electrochemical device.

[0068] In one embodiment of the present application, the mass percentage content of the molecular modifier is b, 0.1%≤b≤15.0%, based on the total mass of the modified melamine salt. Illustratively, the value of b can be 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, 10.5%, 11.0%, 11.5%, 12.0%, 12.5%, 13.0%, 14.5%, 15.0% or a range consisting of any two of the above values. By regulating the value of the mass percentage content b of the molecular modifier in the above range, the molecular modifier has a suitable amount, and during the synthesis of the modified melamine salt, the probability of the molecular modifier destroying the structure of the melamine salt is low, the molecular modifier bonds with the melamine salt molecule, the reaction is complete, and the probability of the molecular modifier existing as a pure substance in the reaction system is reduced. In this way, the modified melamine salt prepared has a suitable difference in endothermic temperature compared to the same type of unmodified melamine salt. Thus, the high-temperature storage performance and mechanical safety performance of the electrochemical device can be improved.

[0069] In one embodiment of the present application, 0.5%≤b≤5.0%. Illustratively, the value of b can be 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0% or a range consisting of any two of the above values. By regulating the value of the mass percentage content b of the molecular modifier in the above range, the molecular modifier can further react completely with the melamine salt, and the probability of the molecular modifier existing as a pure substance in the reaction system is reduced. In this way, the modified melamine salt prepared has a suitable difference in endothermic temperature compared to the same type of unmodified melamine salt. Thus, the high-temperature storage performance and mechanical safety performance of the electrochemical device can be further improved.

[0070] In one embodiment of this application, the absolute value of the pH difference between the modified melamine salt and the binder is m, where 0 ≤ m ≤ 5.0. Exemplarily, the value of m can be 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, or a range of any two of the above values. By controlling the absolute value m of the pH difference between the modified melamine salt and the binder within the above range, the pH difference between the binder and the modified melamine salt can be reduced. This reduces the possibility of agglomeration of the binder and modified melamine salt into large particles during the mixing process due to acid-base imbalance, ensuring uniform dispersion of the binder. This reduces problems such as missed coating, clogging, and excessive thickness during coating, and improves the lithium ion and electron transport capacity in the coating composition, thereby enhancing the high-temperature storage performance and mechanical safety performance of the electrochemical device.

[0071] In one embodiment of this application, 0 ≤ m ≤ 2.5. Exemplarily, the value of m can be 0, 0.5, 1.0, 1.5, 2.0, 2.5, or a range consisting of any two of the above values. By controlling the absolute value m of the pH difference between the modified melamine salt and the binder within the above range, the pH difference between the binder and the modified melamine salt can be further reduced. This further reduces the agglomeration of the binder and modified melamine salt into large particles during the mixing process due to acid-base imbalance, reducing the possibility of problems such as missed coating, clogging, and excessive thickness caused by large particles during coating. Simultaneously, it reduces the possibility of lithium ion and electron transport being hindered by large particles. This further improves the high-temperature storage performance and mechanical safety performance of the electrochemical device.

[0072] This application does not impose any particular restrictions on the method of controlling the absolute value m of the pH difference, as long as it achieves the purpose of this application. For example, it can be achieved by mixing the same modified melamine salt with different types of binders or by mixing the same binder with modified melamine salts of different pH values.

[0073] A second aspect of this application provides an electrochemical device comprising the coating composition of any of the foregoing embodiments, thereby providing the electrochemical device with good high-temperature storage performance and mechanical safety performance.

[0074] In one embodiment of the present application, the electrochemical device further comprises a positive electrode sheet and a separator, and the coating composition is disposed on a surface of the separator facing the positive electrode sheet and / or at least one surface of the positive electrode sheet. For example, in some embodiments, the coating composition can be disposed on one surface of the separator facing the positive electrode sheet along the thickness direction of the separator. In other embodiments, the coating composition is disposed on one surface of the separator facing the positive electrode sheet along the thickness direction of the separator, and the coating composition is also disposed on one surface of the positive electrode sheet along the thickness direction of the positive electrode sheet. In still other embodiments, the coating composition is disposed on one surface of the separator facing the positive electrode sheet along the thickness direction of the separator, and the coating composition is also disposed on both surfaces of the positive electrode sheet along the thickness direction of the positive electrode sheet. It should be noted that the "surface" herein can be the entire area of the surface of the positive electrode sheet or the separator, or can be a partial area of the surface of the positive electrode sheet or the separator, and the present application is not particularly limited as long as the purpose of the present application can be achieved.

[0075] In the present application, the positive electrode tab includes a positive current collector and a positive material layer disposed on at least one surface of the positive current collector. The "positive material layer disposed on at least one surface of the positive current collector" means that the positive material layer can be disposed on one surface of the positive current collector along the thickness direction of the positive current collector, or can be disposed on two surfaces of the positive current collector along the thickness direction of the positive current collector. It should be noted that the "surface" herein can be the entire area of the surface of the positive current collector, or can be part of the area of the surface of the positive current collector, which is not particularly limited in the present application as long as the purpose of the present application can be achieved. The positive current collector is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, it can include an aluminum foil, an aluminum alloy foil, or a composite current collector (for example, an aluminum-carbon composite current collector), etc. The positive material layer includes a positive active material, which is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, the positive active material can include but is not limited to at least one of nickel-cobalt-manganese lithium phosphate (for example, NCM811, NCM622, NCM523, NCM111), nickel-cobalt-aluminum lithium phosphate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobaltate (LiCoO2), lithium manganate, lithium manganese iron phosphate, or lithium titanate. The positive material layer can further include a conductive agent and a positive binder, which are not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, the conductive agent can include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials, or conductive polymers, and the conductive carbon black can include but is not limited to at least one of acetylene black or ketjen black. The above-mentioned carbon nanotubes can include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers can include but are not limited to vapor-grown carbon fibers (VGCF) and / or nanometer carbon fibers. The above-mentioned metal materials can include but are not limited to metal powder and / or metal fibers, and specifically, the metal can include but is not limited to at least one of copper, nickel, aluminum, or silver. The above-mentioned conductive polymer can include but is not limited to at least one of polyphenylene derivative, polyaniline, polythiophene, polyacetylene, or polypyrrole. The positive binder can include but is not limited to at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, butadiene-styrene rubber, or polyvinylidene fluoride. The thickness of the positive current collector and the positive material layer is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the thickness of the positive current collector is 5 μm to 20 μm, and the thickness of the positive material layer is 30 μm to 120 μm. Optionally, the positive electrode tab can further include a conductive layer, which is located between the positive current collector and the positive material layer. The composition of the conductive layer is not particularly limited and can be a commonly used conductive layer in the art. The conductive layer includes a conductive agent and a positive binder.The conductive agent in the conductive layer and the positive electrode binder are not particularly limited in the present application, and for example, can be at least one of the above-described conductive agent and the above-described positive electrode binder.

[0076] The separator is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, in an embodiment of the present application, the material of the separator can include, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) based on polypropylene (PP), polyester (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of the separator can include at least one of a woven film, a non-woven film, a microporous film, a composite film, a calendered film, or a spunlaced film.

[0077] In an embodiment of the present application, the separator can include a base material and a surface treatment layer. The base material can be a non-woven fabric or a composite film having a porous structure, and the material of the base material can include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used. Optionally, a surface treatment layer is provided on at least one surface of the base material, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. In some embodiments of the present application, the inorganic layer includes inorganic particles and a separator binder. The inorganic particles are not particularly limited in the present application, and for example, can include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The separator binder is not particularly limited in the present application, and for example, can be at least one of the above-described positive electrode binder. In some embodiments of the present application, the polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene). In the present application, the thickness of the separator is not particularly limited, as long as the object of the present application can be achieved.

[0078] The preparation method of the positive electrode sheet is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, in some embodiments, the two surfaces of the positive electrode sheet are provided with the coating composition, and the preparation method of the positive electrode sheet can include but is not limited to the following steps: (1) preparation of the semi-finished positive electrode sheet: the positive electrode active material, the conductive agent, and the positive electrode binder are added into N-methyl pyrrolidone, stirred and mixed uniformly to form a positive electrode slurry, the positive electrode slurry is uniformly coated on one side surface of the positive electrode current collector, and then dried, and then the above steps are repeated on the other side surface of the positive electrode current collector to obtain a semi-finished positive electrode sheet coated with positive electrode material layers on both sides. (2) Preparation of the positive electrode sheet: the coating composition is coated on the surface of the positive electrode material layer away from the positive electrode current collector on one side of the semi-finished positive electrode sheet by gravure roll transfer coating, and then the above steps are repeated on the surface of the positive electrode material layer away from the positive electrode current collector on the other side of the semi-finished positive electrode sheet, and then dried to obtain the positive electrode sheet. For example, in other embodiments, only one surface of the positive electrode sheet is provided with the coating composition, and the preparation method of the positive electrode sheet can include but is not limited to the following steps: (1) preparation of the semi-finished positive electrode sheet: the positive electrode active material, the conductive agent, and the positive electrode binder are added into N-methyl pyrrolidone, stirred and mixed uniformly to form a positive electrode slurry, the positive electrode slurry is uniformly coated on one side surface of the positive electrode current collector, and then dried, and then the above steps are repeated on the other side surface of the positive electrode current collector to obtain a semi-finished positive electrode sheet coated with positive electrode material layers on both sides. (2) Preparation of the positive electrode sheet: select any one side of the above semi-finished positive electrode sheet coated with positive electrode material layers on both sides, and coat the coating composition on the side surface of the positive electrode material layer away from the positive electrode current collector by gravure roll transfer coating, and then dried to obtain the positive electrode sheet. For example, in still other embodiments, the preparation method of the positive electrode sheet can include but is not limited to the following steps: the positive electrode active material, the conductive agent, and the positive electrode binder are added into N-methyl pyrrolidone, stirred and mixed uniformly to form a positive electrode slurry, the positive electrode slurry is uniformly coated on one side surface of the positive electrode current collector, and then dried, and then the above steps are repeated on the other side surface of the positive electrode current collector to obtain a positive electrode sheet coated with positive electrode material layers on both sides.

[0079] The mass ratio of the positive electrode active material, the conductive agent, and the positive electrode binder is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the mass ratio of the positive electrode active material, the conductive agent, and the positive electrode binder can be (95 to 98):(1 to 5):(1 to 3). The solid content of the positive electrode slurry is not particularly limited in the present application, as long as the purpose of the present application can be achieved. The drying temperature is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the drying temperature can be 90°C to 130°C.

[0080] The preparation method of the separator is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, in some embodiments, the separator is provided with a coating composition on the surface thereof facing the positive electrode tab, and the preparation method of the separator can include, but is not limited to, the following steps: preparing a substrate, transferring and coating the coating composition onto the surface of the substrate facing the positive electrode tab by means of gravure roll transfer coating, and drying in an oven at 45-60°C to obtain the separator. The above-mentioned substrate can also be obtained by purchase.

[0081] In the present application, the electrochemical device further comprises a negative electrode tab, which comprises a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The "negative electrode material layer provided on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be provided on one surface of the negative electrode current collector along the thickness direction thereof, or can be provided on two surfaces of the negative electrode current collector along the thickness direction thereof. It should be noted that the "surface" herein can be the entire area of the surface of the negative electrode current collector, or can be a partial area of the surface of the negative electrode current collector, which is not particularly limited in the present application, as long as the purpose of the present application can be achieved. The negative electrode current collector is not particularly limited in the present application, as long as the purpose of the present application can be achieved, for example, it can comprise a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam or a composite current collector, exemplarily, the composite current collector can be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc. The negative electrode material layer comprises a negative electrode active material, which is not particularly limited in the present application, as long as the purpose of the present application can be achieved, for example, the negative electrode active material can comprise, but is not limited to, natural graphite, artificial graphite, mesocarbon microbeads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured Li4Ti5O12, etc. 12Li-Al alloy. In some embodiments of the present application, the negative material layer can further include a conductive agent and a negative binder, and the present application does not particularly limit the kinds of the conductive agent and the negative binder as long as the purpose of the present application can be achieved, for example, at least one of the above-mentioned conductive agent and the above-mentioned positive binder. The present application does not particularly limit the mass ratio of the negative active material, the conductive agent, and the negative binder in the negative material layer, and a person skilled in the art can select according to the actual needs as long as the purpose of the present application can be achieved. The present application does not particularly limit the thickness of the negative material layer as long as the purpose of the present application can be achieved, for example, the thickness of the single-sided negative material layer is 30 μm to 120 μm. The present application does not particularly limit the thickness of the negative current collector as long as the purpose of the present application can be achieved, for example, the thickness of the negative current collector is 4 μm to 15 μm. Optionally, the negative electrode sheet can further include a conductive layer between the negative current collector and the negative material layer. The present application does not particularly limit the composition of the conductive layer, which can be a commonly used conductive layer in the art. For example, the conductive layer includes a conductive agent and a negative binder. The present application does not particularly limit the conductive agent and the negative binder in the conductive layer, which can be at least one of the above-mentioned conductive agent and the above-mentioned negative binder.

[0082] In the present application, the electrochemical device further includes an electrolyte including a lithium salt and a non-aqueous solvent. The present application does not particularly limit the lithium salt as long as the purpose of the present application can be achieved. For example, the lithium salt can include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. The present application does not particularly limit the content of the lithium salt in the electrolyte as long as the purpose of the present application can be achieved. In the present application, the non-aqueous solvent includes ethylene carbonate, a carboxylic ester compound, and a fluoroethylene carbonate (FEC) compound. The above-mentioned carboxylic ester compound can include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone, or caprolactone. The present application does not particularly limit the content of the non-aqueous solvent in the electrolyte as long as the purpose of the present application can be achieved.

[0083] The electrochemical device of the present application further includes a packaging bag for containing the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte, and other components in the electrochemical device known in the art, and the present application does not limit the above-mentioned other components. The present application does not particularly limit the packaging bag, which can be a commonly known packaging bag in the art as long as the purpose of the present application can be achieved.

[0084] The kind of the electrochemical device according to the present application is not particularly limited, and it can include any device in which an electrochemical reaction occurs. In the present application, the electrochemical device can include, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery (lithium ion polymer battery), and the like.

[0085] The preparation process of the electrochemical device according to the present application is well known to those skilled in the art, and the present application is not particularly limited, for example, the preparation process of the electrochemical device can include, but is not limited to, the following steps: stacking the separator, the positive electrode sheet, the separator, and the negative electrode sheet in order, and winding, folding, or the like as needed to obtain an electrode assembly in a wound structure, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag and sealing it to obtain an electrochemical device. Alternatively, the separator, the positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, and then the four corners of the entire stacked structure are fixed with adhesive tape to obtain an electrode assembly in a stacked structure, the electrode assembly is placed in a packaging bag, an electrolyte is injected into the packaging bag and sealed to obtain an electrochemical device. In addition, a current overprotection element, a guide plate, or the like can also be placed in the packaging bag as needed to prevent the pressure inside the electrochemical device from rising and overcharging and discharging.

[0086] The third aspect of the present application provides an electronic device comprising the electrochemical device according to any one of the preceding embodiments. Therefore, the electronic device has good high-temperature storage performance and mechanical safety performance.

[0087] The kind of the electronic device according to the present application is not particularly limited, and it can be any electronic device known in the art. In some embodiments of the present application, the electronic device can include, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a head-mounted stereo headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, a power tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor, and the like.

[0088] Examples

[0089] Hereinafter, examples and comparative examples are given to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods.

[0090] Test methods and apparatus:

[0091] Heat absorption temperature test:

[0092] After the lithium ion battery is discharged at 0.1C constant current to 3.0V, the lithium ion battery is disassembled to obtain the positive electrode sheet with the coating. The positive electrode sheet is cleaned with N-methyl pyrrolidone to separate the modified melamine salt from the positive electrode sheet, and the modified melamine salt is obtained by filtering and drying at 85°C. The endothermic temperature of the modified melamine salt is measured by a differential scanning calorimeter. The endothermic temperature of the unmodified melamine salt can be obtained by directly purchasing the same type of unmodified melamine salt and measuring it by the differential scanning calorimeter. Δt is the difference between the endothermic temperatures of the unmodified melamine salt and the modified melamine salt.

[0093] It should be noted that the "coating" described above refers to a coating containing a coating composition, and "coating" appearing hereinafter also refers to a coating containing a coating composition.

[0094] Thermogravimetric mass residual rate test:

[0095] After the lithium ion battery is discharged at 0.1C constant current to 3.0V, the lithium ion battery is disassembled to obtain the positive electrode sheet with the coating. The coating is scraped off to obtain a coating powder. The obtained coating powder is soaked and cleaned with NMP solution for 2 to 3 times to remove residual lithium salt and adhesive layer, and then placed in a vacuum oven at 80°C for drying to remove the solvent. 5mg to 15mg of the powder is spread on the crucible of the thermogravimetric analyzer, and the mass change of the sample is continuously measured by a balance during the programmed temperature process. The test temperature range is room temperature to 600°C. The test atmosphere is set in nitrogen (N2) atmosphere.

[0096] Scanning electron microscope test:

[0097] After the lithium ion battery is discharged at 0.1C constant current to 3.0V, the lithium ion battery is disassembled to obtain the positive electrode sheet with the coating, and the length and width are 20mm×20mm. NMP solution is added dropwise to the surface of the positive electrode sheet with the coating to clean the lithium salt, and then the positive electrode sheet is dried in an 80°C air oven. The positive electrode sheet is cut to obtain a test sample with a size of 5mm×5mm, which is attached to a conductive tape, and then subjected to gold spraying treatment. The morphology photo is obtained by using a Zeiss analytical scanning electron microscope.

[0098] Modified melamine salt content test:

[0099] After the lithium ion battery is discharged at 0.1C constant current to 3.0V, the lithium ion battery is disassembled to obtain the positive electrode sheet with the coating. The positive electrode sheet is cleaned with N-methyl pyrrolidone to separate the modified melamine salt from the positive electrode sheet, and a suspension containing the coating is obtained. Half of the suspension is filtered and dried at 85°C, and the weight of the modified melamine salt M1 is measured. The other half is not filtered and dried at 85°C, and the weight of the coating composition M2 is measured. The mass percentage of melamine salt in the coating composition = M1 / M2×100%.

[0100] Particle size test:

[0101] After the lithium ion battery is discharged at 0.1C constant current to 3.0V, the lithium ion battery is disassembled to obtain the positive electrode sheet with coating. The positive electrode sheet is cleaned with N-methyl pyrrolidone to separate the modified melamine salt from the positive electrode sheet, and the modified melamine salt is obtained by filtering and drying at 85°C. The modified melamine salt powder is dispersed in deionized water or alcohol, and sodium hexametaphosphate dispersant is added, and ultrasonic stirring is performed for 10 min. The modified melamine salt is tested by using a Malvern particle size tester (model MasterSizer 2000) to obtain the particle size Dv50 of the modified melamine salt.

[0102] Solubility test:

[0103] Preparation of test electrolyte: ethylene carbonate, propylene carbonate (PC) and diethyl carbonate (DEC) are mixed in a mass ratio of 1:3:6 as a base solvent, lithium salt LiPF6, ethyl acetate and fluoroethylene carbonate are mixed and added to the base solvent, and stirred uniformly to obtain the test electrolyte. Among them, based on the mass of the test electrolyte, the mass percentage of lithium salt LiPF6 is 15%, the mass percentage of ethyl acetate is 5%, the mass percentage of fluoroethylene carbonate is 5%, and the balance is the base solvent.

[0104] After the lithium ion battery is discharged at 0.1C constant current to 3.0V, the lithium ion battery is disassembled to obtain the positive electrode sheet with coating. The positive electrode sheet is cleaned with N-methyl pyrrolidone to separate the modified melamine salt from the positive electrode sheet, and the modified melamine salt is obtained by filtering and drying at 85°C.

[0105] Take the modified melamine salt, the weight is 0.5g, put it in 5g test electrolyte, store at 85°C for 1h, filter the modified melamine salt, and dry to obtain the weight of the modified melamine salt W. The solubility calculation formula is s1(g / g)=(0.5-W) / W / 5.

[0106] High temperature storage performance test:

[0107] In an environment of about 25°C, the lithium ion battery is charged at a constant current of 0.5C to a voltage of about 4.5V, and charged at a constant voltage of 4.5V until the current is less than 0.05C, so that the lithium ion battery is in a full charge state of 4.25V. The thickness of the lithium ion battery is tested. Then the lithium ion battery in the full charge state is placed in an oven at about 85°C for about 24h, and then the thickness after storage is tested. The high temperature storage expansion rate of the lithium ion battery is calculated by the following formula:

[0108] High temperature storage expansion rate (%) = ((thickness after storage-thickness before storage) / thickness before storage) x 100%.

[0109] Passing rate test of impact test:

[0110] The lithium ion battery was placed at 25°C for 15 min to reach a constant temperature state, and was charged at 1C constant current to a voltage of 4.5V, and was charged at 4.5V constant voltage to a current of 0.05C.

[0111] In a 25°C test environment, the lithium ion battery was placed on the test table with the side with the cell code information facing up. A 15.8mm diameter rod was placed in the center of the wide face of the lithium ion battery, with the rod perpendicular to the long axis of the lithium ion battery. A 9.1±0.1kg weight was dropped vertically from a height of 610±25mm in a free state, and fell on the intersection of the rod and the lithium ion battery. The passing criteria were: no fire, no explosion.

[0112] Each example and comparative example was tested with 20 lithium ion batteries, and the passing rate (%) of the impact test = the number of passes / 20 x 100%.

[0113] Compression test:

[0114] The lithium ion battery was placed at 25°C for 15 min to reach a constant temperature state, and was charged at 1C constant current to a voltage of 4.5V, and was charged at 4.5V constant voltage to a current of 0.05C.

[0115] In a 25°C test environment, the lithium ion battery was placed on the test table, and a blunt nail with a diameter of 6mm was used to test at a pressure rate of 300N / min, starting from the head step of the lithium ion battery at a position 10±1mm from the upper edge of the main body, until the lithium ion battery exploded or caught fire, and the compression pressure (N) at that time was recorded.

[0116] Example 1-1

[0117] Preparation of coating composition

[0118] (1) Preparation of modified melamine polyphosphate: 2000ml of deionized water was added to a 5L reaction vessel, heated to 85°C, and 200g of melamine (C3N6H6) was added under stirring at 300rpm. After the melamine was highly dispersed, stirring was continued for 30min to obtain a highly dispersed melamine precursor solution. 98g of pre-milled phosphoric acid powder and 4g of glycerol were added, and the temperature was controlled at 85°C. The solution was stirred rapidly at 500rpm for 15min, and then 100g of phosphoric acid powder was added. The reaction was carried out at 95°C for 30min. After the reaction was cooled to room temperature, the filtrate was filtered, and the filter cake was washed twice with an equal amount of 79°C deionized water. The modified melamine polyphosphate was spray-dried and dried to obtain a white powder solid.

[0119] (2) Preparation of coating composition 1: In a 20L dispersion tank, 3kg of the above modified melamine polyphosphate and 0.3kg of polyvinylidene fluoride binder were added, with a mass ratio of 10:1, a total of 3.3kg, 11.7kg of N-methyl pyrrolidone (NMP) solvent was added, and uniformly dispersed and mixed to obtain coating composition 1.

[0120] (3) Preparation of coating composition 2: In a 20L dispersion tank, 3kg of the above modified melamine polyphosphate and 0.3kg of polyacrylic acid binder were added, with a mass ratio of 10:1, a total of 3.3kg, 11.7kg of deionized water was added, and uniformly dispersed and mixed to obtain coating composition 2.

[0121] <Preparation of positive electrode sheet>

[0122] The positive electrode active material lithium cobaltate, the conductive agent conductive carbon black (Super P), and the binder polyvinylidene fluoride (PVDF, weight average molecular weight Mw=530000) were added to N-methyl pyrrolidone (NMP) in a mass ratio of 96:2.5:1.5, stirred uniformly to form a positive electrode slurry with a solid content of 70wt%. The positive electrode slurry was uniformly coated on one side of the positive electrode current collector aluminum foil, dried at 85°C, and then the above steps were repeated on the other side of the aluminum foil to obtain a semi-finished positive electrode sheet with positive electrode material layers coated on both sides. After cold pressing and cutting, a semi-finished positive electrode sheet with a size of 74mm×867mm was obtained. The coating composition 1 was transferred and coated onto the surface of the positive electrode material layer of the semi-finished positive electrode sheet away from the positive electrode current collector using a gravure roll, and then the above steps were repeated on the surface of the positive electrode material layer of the semi-finished positive electrode sheet away from the positive electrode current collector, and dried in an oven at 85°C to obtain a positive electrode sheet. The coating weight of the coating composition on both sides of the positive electrode sheet was 6mg / 5000mm 2 .

[0123] <Preparation of separator>

[0124] The substrate was a polyethylene polymer microporous membrane (from Ennew Material Technology Co., Ltd.) with a thickness of 5μm and a porosity of 55%. The coating composition 2 was transferred and coated onto the surface of the substrate facing the positive electrode sheet using a gravure roll, and dried in an oven at 55°C to obtain a separator. The coating weight of the coating composition on the substrate was 10mg / 5000mm 2 .

[0125] <Preparation of negative electrode sheet>

[0126] The negative active material artificial graphite, thickening agent sodium carboxymethyl cellulose (CMC) and binder styrene-butadiene rubber (SBR) were added into deionized water in a mass ratio of 96:2:2, and stirred uniformly to form a negative electrode slurry with a solid content of 50wt%. The negative electrode slurry was uniformly coated on one side surface of the negative electrode current collector copper foil, dried, and then the above steps were repeated on the other side surface of the copper foil to obtain a negative electrode sheet coated with a negative electrode active layer on both sides. After cold pressing and cutting, a negative electrode sheet with a specification of 74mm x 867mm was obtained.

[0127] <Preparation of electrolyte>

[0128] In an argon atmosphere glove box with a water content of less than 10ppm, ethylene carbonate, ethyl acetate and fluoroethylene carbonate (FEC) were uniformly mixed in a mass ratio of 55:30:15 to obtain a base solvent, and lithium salt LiPF6 was added and stirred uniformly to obtain an electrolyte. Among them, the mass percentage of lithium salt LiPF6 based on the total mass of the electrolyte is 12.5%, and the balance is the base solvent.

[0129] <Preparation of lithium ion battery>

[0130] The prepared separator, positive electrode sheet, separator, negative electrode sheet were stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to obtain a laminated electrode assembly. After welding the positive electrode tab and the negative electrode tab, the electrode assembly was placed in a packaging bag of aluminum plastic film, heat sealed around, leaving a liquid injection port, and the above electrolyte was injected. After vacuum packaging, standing, formation, degassing and other processes, a lithium ion battery was obtained.

[0131] Example 1-2

[0132] <Preparation of coating composition>

[0133] (1) Preparation of modified melamine cyanurate: 2000ml deionized water was added to a 5L reaction vessel, heated to 85℃, and 200g melamine (C3N6H6) was added under stirring at 300rpm. After the melamine was highly dispersed, continuous stirring was carried out for 30min to obtain a highly dispersed melamine precursor solution. 163g of pre-milled cyanuric acid powder and 4g of glycerol were added, and the temperature was controlled at 85℃. Rapid stirring was carried out at 500rpm for 15min, and then 163g of cyanuric acid powder was added. The reaction was carried out at 95℃ for 30min. After the reaction was cooled to room temperature, the reaction mixture was filtered, the filter cake was washed twice with an equal amount of 79℃ deionized water, and the modified melamine cyanurate was obtained as a white powder solid after spray granulation and drying.

[0134] In (2) and (3), except that the modified melamine polyphosphate was replaced by modified melamine cyanurate, the rest was the same as Example 1-1.

[0135] The preparation of the positive electrode sheet, the preparation of the negative electrode sheet, the preparation of the separator, the preparation of the electrolyte, and the preparation of the lithium ion battery are the same as in Example 1-1.

[0136] Examples 1-3 to 1-9

[0137] The rest is the same as Example 1-2 except that Δt is adjusted according to Table 1. Among them, the adjustment of Δt is realized by adjusting the addition amount of the molecular modifier during the preparation of the coating composition.

[0138] Examples 1-10 to 1-13

[0139] The rest is the same as Example 1-2 except that s1 is adjusted according to Table 1. Among them, the adjustment of s1 is realized by adjusting the reaction temperature of melamine and the molecular modifier during the preparation of the coating composition.

[0140] Examples 1-14 to 1-20

[0141] The rest is the same as Example 1-1 except that the particle size Dv50 of the modified melamine salt is adjusted according to Table 1.

[0142] Example 1-21

[0143] The rest is the same as Example 1-1 except that the coating composition 1 is prepared according to the following steps.

[0144] Preparation of the coating composition

[0145] Preparation of the coating composition 1: In a 20L dispersion tank, 1.485kg of the above modified melamine polyphosphate, 0.16kg of polyvinylidene fluoride binder and 1.685kg of LATP (Li 1.4 Al 0.4 Ti 1.6 (PO4)3) powder with a mass ratio of 45:5:50, a total of 3.33kg, 11.7kg of N-methyl pyrrolidone solvent is added, and uniformly dispersed and mixed to obtain the coating composition 1.

[0146] Examples 1-22 to 1-24

[0147] The rest is the same as Example 1-19 except that the mass percentage content a of the modified melamine salt is adjusted according to Table 1.

[0148] Among them, with the change of the mass percentage content a of the modified melamine salt, the mass percentage content of the binder remains unchanged, and the LATP (Li 1.4 Al 0.4 Ti 1.6The mass percentage of the modified melamine salt is changed, and the mass percentage of the binder is changed accordingly, and the sum of the mass percentages of the modified melamine salt and the binder is 100%.

[0149] Examples 1-25 to 1-28

[0150] The rest is the same as Example 1-1, except that the mass percentage of the modified melamine salt a is adjusted according to Table 1.

[0151] The mass percentage of the modified melamine salt is changed, and the mass percentage of the binder is changed accordingly, and the sum of the mass percentages of the modified melamine salt and the binder is 100%.

[0152] Example 1-29

[0153] The rest is the same as Example 1-1, except that the positive electrode sheet and the separator are prepared according to the following steps.

[0154] <Preparation of the positive electrode sheet>

[0155] The positive electrode active material lithium cobaltate, the conductive agent conductive carbon black (Super P), and the binder polyvinylidene fluoride (PVDF, weight average molecular weight Mw=530000) are added to N-methyl pyrrolidone (NMP) at a mass ratio of 96:2.5:1.5, stirred uniformly to form a positive electrode slurry with a solid content of 70wt%, and the positive electrode slurry is uniformly coated on one side of the positive electrode current collector aluminum foil, dried at 85°C, and then the above steps are repeated on the other side of the aluminum foil to obtain a semi-finished positive electrode sheet coated with a positive electrode material layer on both sides. After cold pressing and cutting, a semi-finished positive electrode sheet with a specification of 74mm×867mm is obtained. The coating composition 1 is transferred and coated onto the surface of the positive electrode material layer on one side of the semi-finished positive electrode sheet away from the positive electrode current collector by means of a gravure roll, and dried in an oven at 85°C to obtain a positive electrode sheet. The coating weight of the coating composition on one side of the positive electrode sheet is 6mg / 5000mm 2 .

[0156] <Preparation of the separator>

[0157] The base material is a polyethylene polymer microporous membrane (from Ennew Material Technology Co., Ltd.) with a thickness of 5μm and a porosity of 55%.

[0158] Example 1-30

[0159] The rest is the same as Example 1-1, except that the positive electrode sheet is prepared according to the following steps.

[0160] <Preparation of the positive electrode sheet>

[0161] The positive electrode active material lithium cobaltate, the conductive agent conductive carbon black (Super P), and the binder polyvinylidene fluoride (PVDF, weight average molecular weight Mw=530000) were added into N-methyl pyrrolidone (NMP) in a mass ratio of 96:2.5:1.5, stirred uniformly to form a positive electrode slurry with a solid content of 70wt%, and the positive electrode slurry was uniformly coated on one side surface of the positive electrode current collector aluminum foil, dried at 85°C, and then the above steps were repeated on the other side surface of the aluminum foil to obtain a semi-finished positive electrode sheet coated with a positive electrode material layer on both sides. After cold pressing and cutting, a positive electrode sheet with a specification of 74mm×867mm was obtained.

[0162] Examples 2-1 to 2-3

[0163] The rest was the same as Example 1-1 except that the type of molecular modifier was adjusted according to Table 2.

[0164] Example 2-4

[0165] The rest was the same as Example 1-1 except that the type of binder was adjusted according to Table 2.

[0166] Examples 2-5 to 2-10

[0167] The rest was the same as Example 1-1 except that the mass percentage content b of the molecular modifier was adjusted according to Table 2.

[0168] Wherein, when the mass percentage content b of the molecular modifier changes, the mass percentage content of the inorganic or organic acid and the mass percentage content of the melamine change accordingly, and the functional group molar ratio of the inorganic or organic acid and the melamine remains unchanged at 101:79. The sum of the mass percentage contents of the inorganic or organic acid, the melamine, and the molecular modifier is 100%.

[0169] Examples 2-11 to 2-16

[0170] The rest was the same as Example 1-1 except that the absolute value m of the pH difference of the modified melamine salt and the binder was adjusted according to Table 2. Wherein, the change of the absolute value m of the pH difference can be achieved by mixing the same type of modified melamine salt with different types of binders.

[0171] Comparative Example 1

[0172] The rest was the same as Example 1-1 except that the positive electrode sheet and the separator were prepared according to the following steps.

[0173] <Preparation of the positive electrode sheet>

[0174] The positive electrode active material lithium cobaltate, the conductive agent conductive carbon black (Super P), and the binder polyvinylidene fluoride (PVDF, weight average molecular weight Mw=530000) were added into N-methyl pyrrolidone (NMP) in a mass ratio of 96:2.5:1.5, stirred uniformly to form a positive electrode slurry with a solid content of 70wt%, the positive electrode slurry was uniformly coated on one side surface of the positive electrode current collector aluminum foil, dried at 85°C, and then the above steps were repeated on the other side surface of the aluminum foil to obtain a semi-finished positive electrode sheet coated with a positive electrode material layer on both sides, and then a positive electrode sheet with a specification of 74mm×867mm was obtained after cold pressing and cutting.

[0175] <Preparation of the separator>

[0176] The base material was a polyethylene microporous film (from Ennew Material Technology Co., Ltd.) with a thickness of 5μm and a porosity of 55%.

[0177] Comparative Example 2

[0178] Except for the preparation of the positive electrode sheet according to the following steps, the rest was the same as Example 1-2.

[0179] <Preparation of the positive electrode sheet>

[0180] 2000ml of deionized water was added to a 5L reaction vessel, heated to 85°C, and 200g of melamine (C3N6H6) was added under stirring at 300rpm, and after it was highly dispersed, the stirring was continued for 30min to obtain a highly dispersed melamine precursor solution. 98g of pre-milled cyanuric acid powder was added, the temperature was controlled at 85°C, and the stirring was fast at 500rpm for 15min, and then 100g of cyanuric acid powder was added, and the reaction was carried out at 95°C for 30min. After the reaction was cooled to room temperature, it was filtered, the filter cake was washed twice with an equal weight of 79°C deionized water, and the white powder solid melamine cyanurate was obtained by spray granulation and drying.

[0181] The positive electrode active material lithium cobaltate, the conductive agent conductive carbon black (Super P), and the binder polyvinylidene fluoride (PVDF, weight average molecular weight Mw=530000) were added into N-methyl pyrrolidone (NMP) in a mass ratio of 96:2.5:1.5, stirred uniformly to form a positive electrode slurry with a solid content of 70wt%, the positive electrode slurry was uniformly coated on one side surface of the positive electrode current collector aluminum foil, dried at 85°C, and then the above steps were repeated on the other side surface of the aluminum foil to obtain a semi-finished positive electrode sheet coated with a positive electrode material layer on both sides, and then a positive electrode sheet with a specification of 74mm×867mm was obtained after cold pressing and cutting.

[0182] In a 20L dispersion tank, 3kg of modified melamine cyanurate, 0.3kg of polyvinylidene fluoride binder, with a mass ratio of 10:1, a total of 3.3kg, 11.7kg of N-methyl pyrrolidone (NMP) was added, and uniformly dispersed and mixed to obtain a coating slurry. The slurry was transferred and coated on the surface of the positive material layer away from the positive current collector on both sides of the semi-finished positive electrode sheet by means of a gravure roll, and dried in an oven. The coating weight of the coating composition on both sides of the positive electrode sheet was 6mg / 5000mm 2 .

[0183] Comparative Example 3

[0184] Except for adjusting the type of modified melamine salt and the endothermic temperature difference Δt according to Table 1, the rest is the same as Examples 1-2. Among them, the adjustment of Δt is realized by adjusting the addition amount of molecular modifier during the preparation of the coating composition.

[0185] The preparation parameters and performance parameters of each example and comparative example are shown in Table 1 and Table 2.

[0186] Table 1

[0187]

[0188] Note: " / " in Table 1 indicates the absence of the corresponding preparation parameter or substance; "a" in Examples 1-1 to 1-29 and Comparative Example 3 in Table 1 is the mass percentage content of modified melamine salt in coating composition 1; "a" in Example 1-30 is the mass percentage content of modified melamine salt in coating composition 2.

[0189] As can be seen from Examples 1-1 to 1-30 and Comparative Examples 1 to 3, the lithium ion battery of the present application contains modified melamine salt, and the endothermic temperature difference Δt of the modified melamine salt and the unmodified melamine salt is controlled in the range of 5℃≤Δt≤100℃, which can make the lithium ion battery have a lower high-temperature storage expansion rate, while having a higher impact test pass rate and extrusion pressure, indicating that the lithium ion battery of the present application has good high-temperature storage performance and mechanical safety performance. The secondary battery of the comparative example does not contain modified melamine salt or the endothermic temperature difference Δt of the modified melamine salt and the unmodified melamine salt is not in the range of 5℃≤Δt≤100℃, the lithium ion battery of the comparative example has a higher high-temperature storage expansion rate, while having a lower impact test pass rate and extrusion pressure, indicating that the lithium ion battery of the comparative example has poor high-temperature storage performance and safety performance.

[0190] The endothermic temperature difference Δt of the modified melamine salt and the unmodified melamine salt generally affects the high-temperature storage performance and mechanical safety performance of the lithium ion battery. As can be seen from Examples 1-2 to 1-9, Comparative Example 2 and Comparative Example 3, when the endothermic temperature difference Δt of the modified melamine salt and the unmodified melamine salt is controlled within the range of the present application, the lithium ion battery has a lower high-temperature storage expansion rate, and at the same time has a higher impact test pass rate and extrusion pressure, indicating that the lithium ion battery provided by the present application has good high-temperature storage performance and mechanical safety performance.

[0191] The solubility s1 of the modified melamine salt in the test electrolyte generally affects the high-temperature storage performance and mechanical safety performance of the lithium ion battery. As can be seen from Examples 1-2, 1-10 to 1-13, when the solubility s1 of the modified melamine salt in the test electrolyte is controlled within the range of the present application, the lithium ion battery has a lower high-temperature storage expansion rate, and at the same time has a higher impact test pass rate and extrusion pressure, indicating that the lithium ion battery provided by the present application has good high-temperature storage performance and mechanical safety performance.

[0192] The thermal weight loss mass residual rate w of the modified melamine salt generally affects the high-temperature storage performance and mechanical safety performance of the lithium ion battery. As can be seen from Examples 1-1 to 1-9, when the thermal weight loss mass residual rate w of the modified melamine salt characterized on the TG curve is controlled within the range of the present application, the lithium ion battery has a lower high-temperature storage expansion rate, and at the same time has a higher impact test pass rate and extrusion pressure, indicating that the lithium ion battery provided by the present application has good high-temperature storage performance and mechanical safety performance.

[0193] The particle size Dv50 of the modified melamine salt generally affects the high-temperature storage performance and mechanical safety performance of the lithium ion battery. As can be seen from Examples 1-1, 1-14 to 1-20, when the particle size Dv50 of the modified melamine salt is controlled within the range of the present application, the lithium ion battery has a lower high-temperature storage expansion rate, and at the same time has a higher impact test pass rate and extrusion pressure, indicating that the lithium ion battery provided by the present application has good high-temperature storage performance and mechanical safety performance.

[0194] The mass percentage content a of the modified melamine salt based on the mass of the coating composition generally affects the high-temperature storage performance and mechanical safety performance of the lithium ion battery. As can be seen from Examples 1-1, 1-21 to 1-28, when the mass percentage content a of the modified melamine salt is controlled within the range of the present application, the lithium ion battery has a lower high-temperature storage expansion rate, and at the same time has a higher impact test pass rate and extrusion pressure, indicating that the lithium ion battery provided by the present application has good high-temperature storage performance and mechanical safety performance.

[0195] The setting position of the coating composition generally affects the high-temperature storage performance and mechanical safety performance of the lithium ion battery. As can be seen from Example 1-1, Example 1-29 and Example 1-30, when the setting position of the coating composition is regulated within the scope of the present application, the lithium ion battery can have a lower high-temperature storage expansion rate, while having a higher impact test pass rate and extrusion pressure, indicating that the lithium ion battery provided by the present application has good high-temperature storage performance and mechanical safety performance.

[0196] Figure 1 The DSC curve of the modified melamine cyanurate of Example 1-2 of the present application can be seen that the peak temperature of the modified melamine cyanurate of Example 1-2 is 403℃; Figure 2 The DSC curve of the unmodified melamine cyanurate in Comparative Example 2 of the present application can be seen that the peak temperature of the unmodified melamine cyanurate is 443℃; therefore, by comparing the peak temperatures of the two, the difference Δt of the endothermic temperatures of the two is 40℃. Figure 3 The TG curve of the modified melamine cyanurate of Example 1-2 of the present application can be seen that the thermal weight loss mass residual rate of the modified melamine cyanurate is 14.97%. Figure 4 The TG curve of the unmodified melamine cyanurate in Comparative Example 2 of the present application can be seen that the thermal weight loss mass residual rate of the unmodified melamine cyanurate is 0%. Figure 5 The scanning electron microscope photo of the unmodified melamine cyanurate of Comparative Example 2 of the present application can be seen from Figure 5 It can be seen that there is no carbonization area in the unmodified melamine cyanurate. Figure 6 The scanning electron microscope photo of the modified melamine cyanurate of Example 1-2 of the present application can be seen from Figure 6 It can be seen that the modified melamine cyanurate appears a carbonization area, and the product after carbonization can maintain the coating structure, reducing the possibility of further contact short circuit between the positive electrode sheet and the negative electrode sheet. Figure 7 The scanning electron microscope photo of the modified melamine cyanurate of Example 1-4 of the present application can be seen from Figure 7 It can be seen that the modified melamine cyanurate appears a carbonization area, and compared with Figure 6 , the particle size of the product after carbonization is smaller, indicating that the thermal weight loss mass residual rate is smaller.

[0197] Table 2

[0198]

[0199] When the modified melamine salt is prepared by introducing a molecular modifier during the reaction of melamine with an inorganic acid or an organic acid, the type of the molecular modifier generally affects the high-temperature storage performance and mechanical safety performance of the lithium ion battery. As can be seen from Example 1-1, Example 2-1 to Example 2-3, when the type of the molecular modifier is regulated within the scope of the present application, the lithium ion battery can have a lower high-temperature storage expansion rate, while having a higher impact test pass rate and extrusion pressure, indicating that the lithium ion battery provided by the present application has good high-temperature storage performance and mechanical safety performance.

[0200] The coating composition includes the modified melamine salt and a binder, and the type of the binder generally affects the high-temperature storage performance and mechanical safety performance of the lithium ion battery. As can be seen from Example 1-1 and Example 2-4, when the type of the binder in the coating composition is regulated within the scope of the present application, the lithium ion battery can have a lower high-temperature storage expansion rate, while having a higher impact test pass rate and extrusion pressure, indicating that the lithium ion battery provided by the present application has good high-temperature storage performance and mechanical safety performance.

[0201] Based on the total mass of the modified melamine salt, the mass percentage content b of the molecular modifier generally affects the high-temperature storage performance and mechanical safety performance of the lithium ion battery. As can be seen from Example 1-1, Example 2-5 to Example 2-10, by regulating the mass percentage content b of the molecular modifier within the scope of the present application, the lithium ion battery can have a lower high-temperature storage expansion rate, while having a higher impact test pass rate and extrusion pressure, indicating that the lithium ion battery of the present application has good high-temperature storage performance and mechanical safety performance.

[0202] The absolute value m of the pH difference between the modified melamine salt and the binder generally affects the high-temperature storage performance and mechanical safety performance of the lithium ion battery. As can be seen from Example 2-1, Example 2-11 to Example 2-16, by regulating the absolute value m of the pH difference between the modified melamine salt and the binder within the scope of the present application, the lithium ion battery can have a lower high-temperature storage expansion rate, while having a higher impact test pass rate and extrusion pressure, indicating that the lithium ion battery of the present application has good high-temperature storage performance and mechanical safety performance.

[0203] It should be noted that in this document, the terms "comprising", "including", or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or inherent to such a process, method, article or device.

[0204] The various embodiments in the specification are described in a related manner, and the same or similar parts between the various embodiments can be referred to each other, and each embodiment focuses on the difference from other embodiments.

[0205] The above only describes the preferred embodiments of the present application, and is not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An electrochemical device comprising a coating composition, said coating composition comprising a modified melamine salt and a binder, wherein, The endothermic temperature of the modified melamine salt, as characterized by differential scanning calorimetry, is lower than that of the unmodified melamine salt, with a difference of Δt℃, where 35≤Δt≤60. The solubility of the modified melamine salt in the test electrolyte is s1 g / g, where s1 < 0.

1. The test electrolyte is composed of lithium hexafluorophosphate, ethyl acetate, fluoroethylene carbonate, ethylene carbonate, propylene carbonate, and diethyl carbonate. Based on the total mass of the test electrolyte, the mass percentage of lithium hexafluorophosphate is 15%, the mass percentage of ethyl acetate is 5%, the mass percentage of fluoroethylene carbonate is 5%, and the mass ratio of ethylene carbonate, propylene carbonate, and diethyl carbonate is 1:3:

6. Based on the mass of the coating composition, the mass percentage of the modified melamine salt is a%, satisfying 70 ≤ a ≤ 95%; The modified melamine salt is obtained by introducing a molecular modifier during the reaction of melamine with inorganic or organic acids; The molecular modifier includes at least one of polyvinyl alcohol and polyethylene glycol; or, The molecular modifier includes at least one of ethylene glycol, propylene glycol, glycerol, butanediol, hexanediol, ethylenediaminetetraacetic acid, trimethylolethane, xylitol, or sorbitol; or, The molecular modifier includes at least one of ethylenediamine or hexamethylenetetramine.

2. The electrochemical device according to claim 1, wherein, s1≤0.02。 3. The electrochemical device according to claim 1, wherein, The residual mass of the modified melamine salt, as characterized by thermal weight loss on the thermogravimetric curve, is w%, 1≤w≤35.

4. The electrochemical device according to claim 3, wherein, 4.56≤w≤33。 5. The electrochemical device according to claim 1, wherein, The modified melamine salt has a particle size of Dv50μm, satisfying 0.1≤Dv50≤3.

0.

6. The electrochemical device according to claim 5, wherein, 0.3≤Dv50≤1.

5.

7. The electrochemical device according to claim 1, wherein, The adhesive includes at least one of polyacrylic acid, polyacrylate, polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyvinyl alcohol, polyimide, or aluminum hydroxide sol.

8. The electrochemical device according to claim 1, wherein, The inorganic acid includes at least one of phosphoric acid, pyrophosphate, or boric acid; the organic acid includes at least one of cyanuric acid, phthalic acid, oxalic acid, phytic acid, or 2-carboxyethylphenylphosphonic acid.

9. The electrochemical device according to claim 1, wherein, Based on the total mass of the modified melamine salt, the mass percentage of the molecular modifier is b%, satisfying 0.1 ≤ b ≤ 15.

0.

10. The electrochemical device according to claim 9, wherein, 0.5≤b≤5.0。 11. The electrochemical device according to claim 1, wherein, The absolute value of the pH difference between the modified melamine salt and the adhesive is m, which satisfies 0 ≤ m ≤ 5.

0.

12. The electrochemical device according to claim 11, wherein, 0≤m≤2.5。 13. The electrochemical device according to any one of claims 1 to 12, wherein the electrochemical device comprises a positive electrode and a separator, wherein, The coating composition is disposed on the surface of the diaphragm facing the positive electrode and / or at least one surface of the positive electrode.

14. An electronic device, wherein, The electronic device includes the electrochemical device according to any one of claims 1 to 13.

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