A secondary battery and its preparation method and application

Abstract

The present invention provides a secondary battery and a preparation method and application thereof, wherein the secondary battery comprises a positive electrode sheet and a negative electrode sheet, and the N / P ratio of the secondary battery satisfies: N / P≥θ N / θ P , where the θ P is the positive electrode first effect, the θ N The N / P of the secondary battery of the present invention meets a specific lower limit, which is not limited to being greater than 1, but is combined with the positive and negative electrode first effects, so that the secondary battery can maximize the energy density while ensuring safety.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries and relates to a secondary battery and a preparation method and application thereof. Background Art

[0002] The working principle of sodium-ion batteries is similar to that of lithium-ion batteries. With the rapid advancement of the industrialization of sodium-ion batteries, it is expected to promote the further development of electric vehicles and energy storage systems.

[0003] As we all know, the core of secondary batteries lies in the cell design. In the cell design, N / P (the ratio of negative electrode capacity to positive electrode capacity) will directly affect the energy density, cycle life and safety performance of the secondary battery. Therefore, the reasonable N / P formula design is very important. The calculation formula of N / P ratio is: N / P=negative electrode active material gram capacity×negative electrode surface density×negative electrode active material content ratio÷(positive electrode active material gram capacity×positive electrode surface density×positive electrode active material content ratio). In design, N / P>1 is generally adopted, that is, the negative electrode capacity is appropriately excessive to avoid the risk of lithium / sodium precipitation on the negative electrode surface of the secondary battery; however, too much excess negative electrode capacity will cause the battery to over-consume the lithium / sodium ions embedded in the negative electrode during the first charge and discharge, resulting in a decrease in the battery energy density. Therefore, when using different positive and negative electrode materials for cell design, it is very meaningful to determine the reasonable range of N / P ratio on the basis of ensuring that lithium / sodium ions do not precipitate lithium / sodium and are used normally.

[0004] Based on the above research, it is necessary to provide a secondary battery whose N / P ratio meets a specific range and can maximize the energy density of the battery cell while ensuring the safety of the battery cell design. Summary of the invention

[0005] The object of the present invention is to provide a secondary battery and a preparation method and application thereof, wherein the N / P value of the secondary battery meets a specific lower limit, which can not only guide the secondary battery to reasonably and effectively improve the energy density of the battery cell according to the N / P while ensuring safety, but also enable the secondary battery to have a higher energy density while ensuring safety.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a secondary battery, the secondary battery comprising a positive electrode sheet and a negative electrode sheet, and the N / P of the secondary battery satisfies:

[0008] N / P ≥ θ N / θ P , where the θ P is the positive electrode first effect, the θ N It is the negative electrode first effect.

[0009] N / P≥θ of the secondary battery of the present invention N / θ P On the basis of ensuring that the secondary battery does not precipitate sodium or lithium, the lower limit of the N / P ratio is accurately designed in combination with the primary effect of the positive and negative electrodes, breaking the mindset that N / P must be greater than 1, and maximizing the energy density of the battery cell. Therefore, the secondary battery of the present invention can have the maximum energy density on the basis of safety; and the lower limit of N / P of the present invention is not limited by the type of positive and negative electrode materials, etc., and has high universality.

[0010] The above-mentioned N / P lower limit derivation process of the present invention (the method for determining the N / P lower limit) is as follows: when θ P >θ N When θ N / θ P When ≤N / P<1, the battery cell will not have sodium / lithium precipitation; when θ P =θ N When N / P ≥ θ N / θ P =1, the battery cell will not have lithium / sodium deposition; when θ P <θ N When N / P≥θ N / θ P When θ>1, the cell will not have lithium / sodium precipitation. Therefore, the lower limit of the N / P ratio is derived, that is, N / P≥θ N / θ P .

[0011] Preferably, when N / P>1, N / P≥θ N / θ P >1.

[0012] Preferably, when N / P<1, θ N / θ P ≤N / P<1.

[0013] Preferably, when N / P=1, N / P≥θ N / θ P =1.

[0014] The present invention provides a lower limit for the N / P ratio, where N / P ≥ θ N / θ P>1 (N / P>1) provides a benchmark for the N / P value of battery cell design, ensuring the safety of battery cell design; θ N / θ P ≤N / P<1 (N / P<1) can effectively improve the energy density of the battery cell by adjusting the N / P ratio without changing the preparation process.

[0015] Preferably, the secondary battery comprises a lithium ion battery or a sodium ion battery.

[0016] Preferably, the secondary battery satisfies C P ≤C N , wherein the C P is the total capacity of the positive electrode for the first charge to remove lithium / sodium, the C N It is the total lithium / sodium insertion capacity of the negative electrode after the first charge.

[0017] The secondary battery of the present invention may be a lithium ion battery or a sodium ion battery; the “ / ” in “lithium / sodium” of the present invention means “or”. For example, when the secondary battery is a lithium ion battery, C P is the total capacity of the positive electrode for the first charge and de-lithiation, C N is the total capacity of lithium embedded in the negative electrode when it is charged for the first time. When the secondary battery is a sodium ion battery, C P is the total capacity of the positive electrode for first charge and sodium removal, C N It is the total sodium insertion capacity of the negative electrode during the first charge.

[0018] The premise of the above lower limit derivation process of the present invention is that C P ≤C N Based on the fact that when C P <C N When C P =C N When the positive electrode is charged for the first time, the lithium / sodium ions released from the positive electrode can be completely embedded in the negative electrode. P ≤C N , it can be ensured that the battery cell does not precipitate lithium / sodium, and on this basis, the lower limit can ensure safety.

[0019] Preferably, the C P =Positive electrode coating surface density × positive electrode active material ratio × positive electrode first charge lithium / sodium desorption gram capacity.

[0020] Preferably, the C N =Negative electrode coating surface density × negative electrode active material ratio × negative electrode first charge lithium / sodium insertion gram capacity.

[0021] Second aspect, the present invention provides a method for preparing a secondary battery as described in the first aspect, the preparation method comprising the following steps:

[0022] Assemble the positive electrode sheet, negative electrode sheet and separator into an electric core, and then inject electrolyte, package, formation and grading to obtain the secondary battery.

[0023] Preferably, the method for preparing the positive electrode sheet includes: mixing a positive electrode active material, a first conductive agent, a first binder and a solvent to prepare a positive electrode active paste, coating the positive electrode active paste on a positive electrode current collector, and obtaining the positive electrode sheet after drying, rolling and punching.

[0024] Preferably, the positive electrode active material of the secondary battery when it is a lithium-ion battery includes any one or a combination of at least two of lithium cobaltate, lithium iron phosphate, lithium manganese iron phosphate, lithium manganate, ternary material lithium nickel cobalt manganate or lithium nickel cobalt aluminate;

[0025] Preferably, the positive electrode active material of the secondary battery when it is a sodium-ion battery includes any one or a combination of at least two of transition metal layered transition metal oxides, tunnel-type transition metal oxides, Prussian blue compounds or polyanion-type compounds. Exemplarily, the structural general formula of the layered transition metal oxide can be represented by Na x1 M1O2, where 0 < x1 ≤ 1, and the position of the transition metal M1 can be occupied by different transition metal ions (such as Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, Ir, Ru, etc.) or alkaline earth metal ions (such as Li, Na, Mg, etc.). Specifically, the layered transition metal oxides include Na 0.67 Ni 0.33 Mn 0.67 O2, Na 0.67 Mn 0.67 Ni 0.33 Mg 0.1 O2, NaNi 0.5 Mn 0.5 O2, NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, NaCu 0.22 Fe 0.30 Mn 0.48 O2 and other materials, and the structural general formula of the tunnel-type transition metal oxide is represented by Na x2 M2O2, where 0 < x2 < 0.5, and M2 includes at least one of Mn and Al. Specifically, the tunnel-type transition metal oxides include Na 0.44 MnO2, Na 0.44 Mn 0.95 Al 0.05 O2 and other materials.

[0026] The chemical formula of the Prussian blue compound includes Na2Fe(CN)6, Na2MnFe(CN)6, Na 0.84 Ni[Fe(CN)6] 0.71 and other materials; the polyanionic compounds include Na3V2(PO4)3, NaVPO4F, Na3V2(PO4)2F3 and other materials.

[0027] Preferably, the first binder comprises PVDF (polyvinylidene fluoride).

[0028] Preferably, the first conductive agent comprises any one of carbon black, activated carbon, carbon nanotubes, Ketjen black, graphene or acetylene black, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of carbon black and activated carbon, or a combination of carbon nanotubes and Ketjen black.

[0029] Preferably, the thickness of the positive electrode current collector is 6-20 μm, for example, 6 μm, 10 μm, 15 μm or 20 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable. The positive electrode current collector includes aluminum foil and / or carbon-coated aluminum foil.

[0030] Preferably, the method for preparing the negative electrode sheet comprises: mixing a negative electrode active material, a second conductive agent, a second binder and a solvent to prepare a negative electrode active slurry, coating the negative electrode active slurry on a negative electrode collector, and obtaining the negative electrode sheet after drying, rolling and punching.

[0031] Preferably, when the secondary battery is a lithium-ion battery, the negative electrode active material includes any one of graphite, amorphous carbon, silicon-based negative electrode material or titanium-based material, or a combination of at least two thereof; illustratively, the graphite includes natural graphite, artificial graphite, composite graphite, mesophase carbon microspheres, etc., the amorphous carbon includes hard carbon and soft carbon, the silicon-based negative electrode material includes silicon-oxygen negative electrode material, silicon-carbon negative electrode material, etc., and the titanium-based material includes lithium titanate.

[0032] Preferably, when the secondary battery is a sodium ion battery, the negative electrode active material includes any one or a combination of at least two of carbon-based materials, alloy materials, metal oxides, metal sulfides, titanium-based materials or organic materials. A typical but non-limiting combination includes a combination of carbon-based materials and alloy materials; illustratively, the carbon-based material includes amorphous carbon such as hard carbon, soft carbon or composite carbon, the alloy material includes Sn, Sb, Ge or SnSb, etc., the metal oxide includes Fe2O3, CuO, CoO, MoO3 or NiCo2O4, etc., the metal sulfide includes MoS2 or SnS, etc., the titanium-based material includes TiO2 and / or NaTi2(PO4)3, and the organic material includes carbonyl compounds, Schiff base compounds, organic free radical compounds or organic sulfides, etc.

[0033] Preferably, the second binder comprises styrene-butadiene copolymer and / or polyacrylic acid.

[0034] Preferably, the second conductive agent comprises any one of carbon black, activated carbon, carbon nanotubes, Ketjen black, graphene or acetylene black, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of carbon black and activated carbon, or a combination of carbon nanotubes and Ketjen black.

[0035] Preferably, the negative electrode active slurry further includes a dispersant, and the dispersant includes carboxymethyl cellulose and / or polyacrylic acid.

[0036] Preferably, the thickness of the negative electrode current collector is 4-15 μm, for example, it can be 5 μm, 10 μm or 15 μm. When the secondary battery is a lithium ion battery, the negative electrode current collector includes copper foil and / or carbon-coated copper foil. When the secondary battery is a sodium ion battery, the negative electrode current collector includes any one of copper foil, aluminum foil, carbon-coated copper foil or carbon-coated aluminum foil.

[0037] Preferably, the solvents used to prepare the positive electrode active slurry and the negative electrode active slurry independently include water or NMP (N-methylpyrrolidone).

[0038] Preferably, when die-cutting the positive and negative electrode sheets, the length and width of the negative electrode after die-cutting are 1-4 mm larger than the length and width of the positive electrode after die-cutting, for example, 1 mm, 2 mm, 3 mm or 4 mm, but not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] In a third aspect, the present invention provides an electronic device, wherein the electronic device comprises the secondary battery as described in the first aspect.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] The present invention explores the lower limit of the N / P ratio range of secondary batteries, combines the relationship between the first effects of positive and negative electrodes, and can quickly and scientifically adjust the N / P ratio of positive and negative electrodes when different positive and negative electrode materials are used for battery cell design. On the basis of ensuring the safety of battery cell design, the energy density of the battery can be improved to the greatest extent. DETAILED DESCRIPTION

[0042] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0043] Example 1

[0044] This embodiment provides a sodium ion battery, which satisfies: N / P≥θ N / θ P >1 and C P ≤C N , where the θ P is the positive electrode first effect, the θ N The first effect of negative electrode, C P is the total capacity of the positive electrode for first charge and removal of sodium, the C N The total sodium insertion capacity of the negative electrode during the first charge;

[0045] N / P=1.073, θ N =90%,θ P =87%,θ N / θ P =1.035; C P = positive electrode coating surface density × positive electrode active material ratio × positive electrode first charge sodium removal gram capacity = 350g / m 2 ×95%×130mAh / g =43225mAh / m 2 , C N = negative electrode coating surface density × negative electrode active material ratio × negative electrode first charge sodium embedding gram capacity = 160g / m 2 ×95%×295mAh / g=44840mAh / m 2 ;

[0046] The preparation method of the sodium ion battery comprises the following steps:

[0047] (1) NaNi 0.35 Fe 0.2 Mg 0.05 Mn 0.4O2, PVDF and conductive carbon black were dispersed in NMP at a mass ratio of 9.5:0.2:0.3 to prepare a positive electrode active slurry, and then the positive electrode active slurry was coated on an aluminum foil with a thickness of 8 μm, and the positive electrode sheet was obtained after drying, rolling and punching. The double-sided surface density of the positive electrode sheet was 350 g / m 2 The compaction density of the positive electrode is 3.1g / cm 3 , the length of the positive electrode sheet is 80mm and the width is 40mm;

[0048] (2) Hard carbon, styrene-butadiene copolymer, carboxymethyl cellulose and conductive carbon black were dispersed in water at a mass ratio of 9.5:0.15:0.15:0.2 to prepare a negative electrode active slurry, and then the negative electrode active slurry was coated on a copper foil with a thickness of 5 μm, and dried, rolled and punched to obtain a negative electrode sheet, wherein the double-sided surface density of the negative electrode sheet was 160 g / m 2 The compaction density of the negative electrode is 0.95g / cm 3 ;

[0049] The length of the negative electrode sheet after die-cutting is 82 mm and the width is 42 mm, both of which are 2 mm larger than the length and width of the positive electrode sheet after die-cutting;

[0050] (3) 15 positive electrode sheets of step (1) and 16 negative electrode sheets of step (2) are selected and assembled with a separator into a laminated soft-pack battery cell by laminating, an electrolyte is injected into the battery cell and the battery cell is packaged, and the sodium ion battery after injection is subjected to formation and capacity separation treatment to obtain a sodium ion battery;

[0051] In the sodium ion battery prepared above, the capacity of the positive electrode of the sodium ion battery cell after the first sodium removal is 2074.8 mAh, and the maximum first sodium embedding capacity of the negative electrode is 2152.3 mAh. Therefore, in theory, the negative electrode can fully accept the sodium ions released from the positive electrode; there is no risk of sodium precipitation.

[0052] Example 2

[0053] This embodiment provides a sodium ion battery, which satisfies: θ N / θ P ≤N / P<1 and C P ≤C N , where the θ P is the positive electrode first effect, the θ N The first effect of negative electrode, C P is the total capacity of the positive electrode for first charge and removal of sodium, the C N The total sodium insertion capacity of the negative electrode during the first charge;

[0054] N / P=0.965, θ N=85%,θ P =90%,θ N / θ P =0.945;

[0055] C P = positive electrode coating surface density × positive electrode active material ratio × positive electrode first charge sodium removal gram capacity = 340g / m 2 ×95%×125mAh / g =40375mAh / m 2 , C N = negative electrode coating surface density × negative electrode active material ratio × negative electrode first charge sodium embedding gram capacity = 155g / m 2 ×95%×280mAh / g =41230mAh / m 2 ;

[0056] The preparation method of the sodium ion battery comprises the following steps:

[0057] (1) NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, PVDF and conductive carbon black were dispersed in NMP at a mass ratio of 9.5:0.2:0.3 to prepare a positive electrode active slurry, and then the positive electrode active slurry was coated on an aluminum foil with a thickness of 20 μm, and a positive electrode sheet was obtained after drying, rolling and punching. The double-sided surface density of the positive electrode sheet was 340 g / m 2 The compaction density of the positive electrode is 3.2g / cm 3 , the length of the positive electrode sheet is 80mm and the width is 40mm;

[0058] (2) Soft carbon, styrene-butadiene copolymer, carboxymethyl cellulose and conductive carbon black were dispersed in water at a mass ratio of 9.5:0.15:0.15:0.2 to prepare a negative electrode active slurry, and then the negative electrode active slurry was coated on a copper foil with a thickness of 15 μm, and then dried, rolled and punched to obtain a negative electrode sheet, wherein the double-sided surface density of the negative electrode sheet was 155 g / m 2 The compaction density of the negative electrode is 1.05g / cm 3 ;

[0059] The length of the negative electrode sheet after die-cutting is 84 mm and the width is 44 mm, both of which are 4 mm larger than the length and width of the positive electrode sheet after die-cutting;

[0060] (3) 15 positive electrode sheets of step (1) and 16 negative electrode sheets of step (2) are selected and assembled with a separator into a laminated soft-pack battery cell by laminating, an electrolyte is injected into the battery cell and the battery cell is packaged, and the sodium ion battery after injection is subjected to formation and capacity separation treatment to obtain a sodium ion battery;

[0061] In the sodium ion battery prepared above, the capacity of the positive electrode of the sodium ion battery cell for the first charge is 1938 mAh, and the maximum initial sodium embedding capacity of the negative electrode is 1979 mAh. Therefore, in theory, the negative electrode can fully accept the sodium ions released from the positive electrode; there is no risk of sodium precipitation.

[0062] Example 3

[0063] This embodiment provides a lithium ion battery, which satisfies: θ N / θ P ≤N / P<1 and C P ≤C N , where the θ P is the positive electrode first effect, the θ N The first effect of negative electrode, C P is the total capacity of the positive electrode for the first charge and de-lithiation, the C N The total lithium insertion capacity of the negative electrode after the first charge;

[0064] N / P=0.990, θ N =92%,θ P =95%,θ N / θ P =0.969;

[0065] C P = positive electrode coating surface density × positive electrode active material ratio × positive electrode first charge lithium removal gram capacity = 310g / m 2 ×95%×150mAh / g =44175mAh / m 2 , C N = Negative electrode coating surface density × Negative electrode active material ratio × Negative electrode first charge lithium embedded capacity = 135g / m 2 ×95%×352mAh / g =45144mAh / m 2 ;

[0066] The preparation method of the lithium ion battery comprises the following steps:

[0067] (1) LiFePO4, PVDF and conductive carbon black were dispersed in NMP at a mass ratio of 9.5:0.2:0.3 to prepare a positive electrode active slurry, and then the positive electrode active slurry was coated on an aluminum foil with a thickness of 13 μm. The positive electrode sheet was obtained by drying, rolling and punching. The double-sided surface density of the positive electrode sheet was 310 g / m 2 The compaction density of the positive electrode is 2.3g / cm 3 , the length of the positive electrode sheet is 80mm and the width is 40mm;

[0068] (2) Graphite, styrene-butadiene copolymer, carboxymethyl cellulose and conductive carbon black were dispersed in water at a mass ratio of 9.5:0.15:0.15:0.2 to prepare a negative electrode active slurry, and then the negative electrode active slurry was coated on a copper foil with a thickness of 15 μm, and dried, rolled and punched to obtain a negative electrode sheet, wherein the double-sided surface density of the negative electrode sheet was 135 g / m 2 The compaction density of the negative electrode is 1.5g / cm 3 ;

[0069] The length of the negative electrode sheet after die-cutting is 84 mm and the width is 44 mm, both of which are 4 mm larger than the length and width of the positive electrode sheet after die-cutting;

[0070] (4) 15 positive electrode sheets of step (1) and 16 negative electrode sheets of step (2) are selected and assembled with a separator into a laminated soft-pack battery cell by laminating, an electrolyte is injected into the battery cell and the battery cell is packaged, and the lithium-ion battery after injection is subjected to formation and capacity separation treatment to obtain a lithium-ion battery;

[0071] In the lithium-ion battery prepared above, the capacity of the positive electrode of the lithium-ion battery cell for the first charge is 2120.5 mAh, and the maximum initial lithium embedding capacity of the negative electrode is 2166.9 mAh. Theoretically, the negative electrode can fully accept the lithium ions released from the positive electrode; there is no risk of lithium plating.

[0072] Comparative Example 1

[0073] This comparative example provides a sodium ion battery, which satisfies: N / P<θ N / θ P , where the θ P is the positive electrode first effect, the θ N The first effect of negative electrode, C P is the total capacity of the positive electrode for first charge and removal of sodium, the C N The total sodium insertion capacity of the negative electrode during the first charge;

[0074] N / P=0.902, θ N =85%,θ P =90%,θ N / θ P =0.945;

[0075] C P = positive electrode coating surface density × positive electrode active material ratio × positive electrode first sodium removal gram capacity = 340g / m 2 ×95%×125mAh / g =40375mAh / m 2 , C N= Negative electrode coating surface density × Negative electrode active material ratio × Negative electrode first charge sodium embedding gram capacity = 145g / m 2 ×95%×280mAh / g =38570mAh / m 2 , through theoretical calculations, it is found that C P >C N , which does not conform to the present invention P ≤C N This basic requirement theoretically raises safety issues regarding sodium precipitation.

[0076] The preparation method of the sodium ion battery comprises the following steps:

[0077] (1) NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, PVDF and conductive carbon black were dispersed in NMP at a mass ratio of 9.5:0.2:0.3 to prepare a positive electrode active slurry, and then the positive electrode active slurry was coated on an aluminum foil with a thickness of 8 μm, and the positive electrode sheet was obtained after drying, rolling and punching. The double-sided surface density of the positive electrode sheet was 340 g / m 2 The compaction density of the positive electrode is 3.2g / cm 3 , the length of the positive electrode sheet is 80mm and the width is 40mm;

[0078] (2) Hard carbon, styrene-butadiene copolymer, carboxymethyl cellulose and conductive carbon black were dispersed in water at a mass ratio of 9.5:0.15:0.15:0.2 to prepare a negative electrode active slurry, and then the negative electrode active slurry was coated on a copper foil with a thickness of 5 μm, and dried, rolled and punched to obtain a negative electrode sheet, wherein the double-sided surface density of the negative electrode sheet was 145 g / m 2 The compaction density of the negative electrode is 1.05g / cm 3 ;

[0079] The length of the negative electrode sheet after die-cutting is 84 cm and the width is 44 cm, both of which are 4 mm larger than the length and width of the positive electrode sheet after die-cutting;

[0080] (3) 15 positive electrode sheets of step (1) and 16 negative electrode sheets of step (2) are selected and assembled with a separator into a laminated soft-pack battery cell by laminating, an electrolyte is injected into the battery cell and the battery cell is packaged, and the sodium ion battery after injection is subjected to formation and capacity separation treatment to obtain a sodium ion battery;

[0081] In the sodium ion battery prepared above, the capacity of the positive electrode of the sodium ion battery cell for the first charge is 1938 mAh, and the maximum sodium embedding capacity of the negative electrode for the first time is 1851.4 mAh. The negative electrode cannot completely accept the sodium ions released from the positive electrode, and the problem of sodium precipitation occurs. Compared with the N / P=0.965 of Example 2, the N / P=0.902 of this comparative example increases with the NP ratio being lower than θ N / θ P =0.945; the battery has a safety problem of sodium precipitation.

[0082] The positive electrode first charge sodium removal / lithium gram capacity, the negative electrode first charge sodium insertion / lithium gram capacity and the positive and negative electrode first efficiency (θ P ,θ N ), are obtained by assembling 2032 button half-cells for actual testing, and the specific testing methods are as follows (it should be noted that all the "positive electrode first charge sodium removal / lithium gram capacity, negative electrode first charge sodium insertion / lithium gram capacity and positive and negative electrode first efficiency" in the present invention can be obtained by the following testing method. Specifically, it is only necessary to use the following battery assembly method and testing method for the positive electrode sheet or negative electrode sheet made in practice to obtain the result):

[0083] (1) For sodium-ion batteries

[0084] Positive electrode: the positive electrode sheet prepared in step (1) of the above Examples 1-2 and Comparative Example 1 is cut into circular electrode sheets with a diameter of 12 mm using a slicer for later use;

[0085] Battery assembly: Dry and weigh the electrode sheets, and then assemble the battery in the glove box. The battery shell type is CR2032, the battery electrodes will be processed pure sodium sheets and round positive plates, the battery separator will be glass fiber (Whatman, GF / C), and the electrolyte will be 1 mol / L NaPF6, EC and DEC with a volume ratio of 1:1. The glove box needs to be protected by high-purity argon gas, and ensure that H2O < 0.01 ppm and O2 < 0.01 ppm.

[0086] Related data test: The present invention adopts the blue electric test system CT2001A for testing. The positive electrode materials of Example 1, Example 2 and Comparative Example 1 of the present invention adopt the charge and discharge voltage window of 2.0-4.0V, and the charge and discharge current adopts 0.1C. The value of the first charge and discharge sodium gram capacity of the charge and discharge is the "positive electrode first charge and discharge sodium gram capacity" mentioned in the present invention. The "positive electrode first efficiency θ P = First discharge sodium embedding capacity in grams after power off / First charge sodium removal capacity in grams after power off"

[0087] Negative electrode: The negative electrode sheet prepared in step (2) of the above Examples 1-2 and Comparative Example 1 is cut into circular electrode sheets with a diameter of 12 mm using a slicer for later use.

[0088] Battery assembly: The electrode sheets are dried and weighed, and then the battery is assembled in a glove box. The battery shell type selected is CR2032, the battery electrodes will use processed pure sodium sheets and round negative electrodes, the battery separator will use glass fiber (Whatman, GF / C), and the electrolyte will use 1 mol / L NaPF6 / EC+DEC (volume ratio is 1:1). The glove box needs to be protected by high-purity argon gas, and ensure that H2O<0.01ppm and O2<0.01ppm.

[0089] Related data test: The present invention adopts the blue electric test system CT2001A for testing. The negative electrode materials of Example 1, Example 2 and Comparative Example 1 of the present invention have a charge and discharge voltage window of 0-2.0V and a charge and discharge current of 0.1C. The value of the first discharge sodium embedding capacity of the negative electrode mentioned in the present invention is the "first charge sodium embedding capacity of the negative electrode". The "first effective θ N = The first charge and discharge sodium removal capacity in grams / the first discharge and discharge sodium embedding capacity in grams.

[0090] (2) For lithium-ion batteries

[0091] Positive electrode: The positive electrode sheet prepared in step (1) of Example 3 above is cut into circular electrode sheets with a diameter of 12 mm using a slicer for later use.

[0092] Battery assembly: Dry and weigh the electrode sheets, and then assemble the battery in the glove box. The battery shell type is CR2032, the battery electrodes will be processed pure lithium sheets and round positive plates, the battery diaphragm will be PP diaphragm, and the electrolyte will be 1mol / L LiPF6 / EC+DEC (volume ratio is 1:1). The glove box needs to be protected by high-purity argon gas, and ensure that H2O<0.01ppm and O2<0.01ppm.

[0093] Related data test: The present invention adopts the blue electric test system CT2001A for testing. The positive electrode material of Example 3 of the present invention adopts the charge and discharge voltage window of 2.0-3.65V and the charge and discharge current adopts 0.1C. The value of the first charge sodium removal gram capacity of the buckled power is the "positive electrode first charge lithium removal gram capacity" mentioned in the present invention. The "positive electrode first effective θ P =Lithium-embedded capacity for the first discharge after power-off / Lithium-removed capacity for the first charge after power-off".

[0094] Negative electrode: The negative electrode sheet prepared in step (2) of Example 3 above is cut into circular electrode sheets with a diameter of 12 mm using a slicer for later use.

[0095] Battery assembly: Dry and weigh the electrode sheets, and then assemble the battery in the glove box. The battery shell type is CR2032, the battery electrodes will be processed pure lithium sheets and round negative electrodes, the battery diaphragm will be PP diaphragm, and the electrolyte will be 1mol / L LiPF6 / EC+DEC (volume ratio is 1:1). The glove box needs to be protected by high-purity argon gas, and ensure that H2O<0.01ppm and O2<0.01ppm.

[0096] Related data test: The present invention adopts the blue electric test system CT2001A for testing. The negative electrode material of Example 3 of the present invention has a charge and discharge voltage window of 0.001V-2.0V in buckle charging, and a charge and discharge current of 0.1C. The value of the first discharge lithium embedded capacity of buckle charging is the "negative electrode first charge lithium embedded capacity" mentioned in the present invention. The "negative electrode first effective θ N =Lithium-free capacity of the first charge after power off / Lithium-embedded capacity of the first discharge after power off".

[0097] Fully charged disassembly to observe lithium / sodium precipitation test: For the sodium ion batteries described in Example 1, Example 2 and Comparative Example 1 of the present invention, after the capacity is divided, constant current charging is performed at 0.33C, and the charging cut-off voltage is 4.0V. The lithium ion battery described in Example 3 of the present invention is charged at 0.33C after the capacity is divided, and the charging cut-off voltage is 3.65V. After obtaining the fully charged batteries of the above embodiments and comparative examples, they are disassembled in the disassembly room, and the sodium / lithium precipitation of the negative electrode sheet is observed. The sodium / lithium precipitation situation is shown in Table 1.

[0098] Table 1

[0099]

[0100] From Table 1 we can see that:

[0101] From the comparison between the embodiment and the comparative example, it can be seen that θ N / θ P As the lower limit of N / P, the secondary battery satisfies N / P and θ N / θ P When the relationship is established, the energy density can be improved to the greatest extent while ensuring safety. Therefore, the lower limit of the N / P interval of the present invention can provide guidance for battery design, and the lower limit is only related to the first effect of the positive and negative electrodes, and is not limited by the types of positive and negative electrode materials, and has high universality.

[0102] In summary, the present invention provides a secondary battery and a preparation method and application thereof, wherein the N / P value of the secondary battery meets a specific lower limit and is not limited to being greater than 1, so that the secondary battery can maximize the energy density of the battery cell while ensuring safety.

[0103] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A secondary battery, characterized in that: The secondary battery comprises a positive electrode sheet and a negative electrode sheet, and the N / P of the secondary battery satisfies: N / P>θ N / θ P , where the θ P is the positive electrode first effect, the θ N It is the first effect of negative electrode; The θ N / θ P As the lower limit of N / P; When N / P>1, N / P>θ N / θ P >1; When N / P<1, θ N / θ P <N / P<1; When N / P=1, N / P>θ N / θ P ; The secondary battery satisfies C P <C N , wherein the C P is the total capacity of the positive electrode for the first charge to remove lithium / sodium, the C N The total capacity of lithium / sodium intercalation for the first charge of the negative electrode; The CP=positive electrode coating surface density×positive electrode active material ratio×positive electrode first charge lithium removal / sodium gram capacity; the CN=negative electrode coating surface density×negative electrode active material ratio×negative electrode first charge lithium insertion / sodium gram capacity.

2. The secondary battery according to claim 1, characterized in that: The secondary battery includes a lithium ion battery or a sodium ion battery.

3. A method for preparing a secondary battery as claimed in claim 1 or 2, characterized in that: The preparation method comprises the following steps: The positive electrode sheet, the negative electrode sheet and the separator are assembled into a battery cell, and then liquid is injected, packaged, formed and capacity divided to obtain the secondary battery.

4. The preparation method according to claim 3, characterized in that: The method for preparing the positive electrode sheet comprises: mixing a positive electrode active material, a first conductive agent, a first binder and a solvent to prepare a positive electrode active slurry, coating the positive electrode active slurry on a positive electrode collector, and drying, rolling and punching to obtain the positive electrode sheet.

5. The preparation method according to claim 3 or 4, characterized in that: When the secondary battery is a lithium-ion battery, the positive electrode active material includes any one of lithium cobalt oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, ternary material lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide, or a combination of at least two thereof; When the secondary battery is a sodium ion battery, the positive electrode active material includes any one of transition metal layered oxides, tunnel-type transition metal oxides, Prussian blue compounds or polyanion compounds, or a combination of at least two thereof.

6. The preparation method according to claim 3 or 4, characterized in that: The method for preparing the negative electrode sheet comprises: mixing a negative electrode active material, a second conductive agent, a second binder and a solvent to prepare a negative electrode active slurry, coating the negative electrode active slurry on a negative electrode current collector, drying, rolling and punching to obtain the negative electrode sheet; When the secondary battery is a lithium-ion battery, the negative electrode active material includes any one of graphite, amorphous carbon, silicon-based negative electrode material or titanium-based material, or a combination of at least two thereof; When the secondary battery is a sodium ion battery, the negative electrode active material includes any one of carbon-based materials, alloy materials, metal oxides, metal sulfides, titanium-based materials or organic materials, or a combination of at least two of them.

7. An electronic device, characterized in that: The electronic device includes the secondary battery according to claim 1 or 2.

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