CN115995550A - Positive electrode active material and application thereof - Google Patents
Positive electrode active material and application thereof Download PDFInfo
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- CN115995550A CN115995550A CN202211075101.6A CN202211075101A CN115995550A CN 115995550 A CN115995550 A CN 115995550A CN 202211075101 A CN202211075101 A CN 202211075101A CN 115995550 A CN115995550 A CN 115995550A
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Abstract
The invention provides a positive electrode active material and application thereof. The positive electrode active material of the present invention includes a metal oxide having a molecular formula shown in formula 1; in an X-ray diffraction pattern, the lithium metal oxide is a Cmca space group of a cubic crystal system and has 002 peaks with 2 theta of 17.9-18.1 degrees and 131 peaks with 2 theta of 67.0-67.5 degrees; li (Li) n‑y Na y Co 1‑a M a O 2 In the formula 1, n is more than or equal to 0.6 and less than or equal to 0.8, y is more than or equal to 0 and less than or equal to 0.05, and a is more than or equal to 0 and less than or equal to 0.2; the molar content ratio m1 of the Li element to the Na element satisfies: m1 is more than or equal to 12 and less than or equal to 80; wherein M is a doping element. The special composition and crystal phase structure of the positive electrode active material are favorable for improving the specific capacity and cycle performance of the battery, and the battery can still be excellent in performance under high-pressure conditions.
Description
Technical Field
The invention relates to a pole piece material, in particular to a positive electrode active material and application thereof, and belongs to the technical field of secondary batteries.
Background
With the development and progress of lithium ion battery technology, the capacity of lithium ion batteries is increasingly required. In the composition of the lithium ion battery, the high and low of the positive electrode active material capacity plays a vital role in the capacity of the lithium ion battery.
In order to increase the capacity of lithium ion batteries, the most commonly used method is to increase the charge-discharge voltage. However, with the increase of voltage, the positive electrode active material has a collapse phenomenon of a crystal structure, so that a series of problems such as rapid capacity decay and great reduction of cycle performance of the battery are caused.
Therefore, developing a lithium ion battery positive electrode active material with high specific capacity and good cycle performance is a technical problem to be solved in the field.
Disclosure of Invention
The invention provides a positive electrode active material, which has a special composition and a crystal phase structure, is favorable for improving the specific capacity and the cycle performance of a battery, and can still make the battery perform excellent especially under high pressure conditions.
The invention provides a positive plate which comprises the positive active material, thereby being beneficial to improving the relevant electrical performance of a battery.
The invention also provides a lithium ion battery which comprises the positive plate, so that the lithium ion battery has excellent performance in specific capacity and cycle performance.
The invention provides a positive electrode active material, wherein the positive electrode active material comprises lithium metal oxide, and the lithium metal oxide has a molecular formula shown in a formula 1;
in an X-ray diffraction pattern, the lithium metal oxide is a Cmca space group of a cubic crystal system and has 002 peaks with 2 theta of 17.9-18.1 degrees and 131 peaks with 2 theta of 67.0-67.5 degrees;
Li n-y Na y Co 1-a M a O 2 1 (1)
In the formula 1, n is more than or equal to 0.6 and less than or equal to 0.8, y is more than or equal to 0 and less than or equal to 0.05, and a is more than or equal to 0 and less than or equal to 0.2;
the molar content ratio m1 of the Li element to the Na element satisfies: m1 is more than or equal to 12 and less than or equal to 80;
wherein M is a doping element.
The positive electrode active material as described above, wherein the lithium metal oxide has a molecular formula shown in formula 2;
Li n-y Na y Co 1-a1-a2 M1 a1 M2 a2 O 2 2, 2
In the formula 2, a1 is more than 0 and less than or equal to 0.1, a2 is more than or equal to 0 and less than or equal to 0.1, a1+a2=a;
wherein M1 is selected from at least one of Te, W, al, B, P and K; m2 is a doping element different from M1.
The positive electrode active material as described above, wherein the positive electrode active material is composed of base particles including the lithium metal oxide and a coating layer covering at least part of the surface of the base particles.
The positive electrode active material as described above, wherein when the cutoff voltage is 3.0 to 3.6V and the SOC is zero, n is 0.7.ltoreq.n.ltoreq.1.0, and the molar content ratio m2 of Li element to Na element satisfies: m2 is more than or equal to 16 and less than or equal to 93.
The positive electrode active material as described above, wherein m2-m1 > 3.
The positive electrode active material as described above, wherein the median particle diameter of the positive electrode active material is 12 μm to 20 μm.
The invention provides a positive plate, wherein the positive plate comprises the positive active material.
The positive plate, wherein the positive plate comprises a current collector, a safety layer and a positive active layer;
the safety layer is clamped between the current collector and the positive electrode active layer, and the positive electrode active layer comprises the positive electrode active material.
The positive electrode sheet as described above, wherein the positive electrode active layer has a compacted density of 3.5g/cm or more 3 。
The invention provides a lithium ion battery, wherein the lithium ion battery comprises the positive plate.
The positive electrode active material has a special crystal phase structure and chemical composition, after the positive electrode active material is applied to a battery, the cycle performance and gram capacity of the battery are remarkably improved, and even under the high-pressure condition of 4.5V and above, the battery using the positive electrode active material can still keep excellent performance of related electric performance, and the problem of structural collapse caused by poor pressure resistance of the positive electrode active material is avoided.
Drawings
Fig. 1 is a schematic view of a portion of a negative electrode sheet of a lithium ion battery according to an embodiment of the invention;
fig. 2 is an SEM image of the positive electrode active material in example 1 of the present invention;
fig. 3 is an SEM image of the positive electrode active material in comparative example 1 of the present invention;
fig. 4 is an XRD pattern of the positive electrode active material in example 1 of the present invention.
Reference numerals illustrate:
20: a negative electrode active layer;
30: a lithium material layer;
101: and a negative electrode current collector.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the technical solutions in the embodiments of the present invention will be clearly and completely described in the following in conjunction with the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The first aspect of the present invention provides a positive electrode active material including a lithium metal oxide having a molecular formula shown in formula 1;
in an X-ray diffraction pattern, the lithium metal oxide is a Cmca space group of a cubic crystal system and has 002 peaks with 2 theta of 17.9-18.1 degrees and 131 peaks with 2 theta of 67.0-67.5 degrees;
Li n-y Na y Co 1-a M a O 2 1 (1)
In the formula 1, n is more than or equal to 0.6 and less than or equal to 0.8, y is more than or equal to 0 and less than or equal to 0.05, and a is more than or equal to 0 and less than or equal to 0.2;
the molar content ratio m1 of the Li element to the Na element satisfies: m1 is more than or equal to 12 and less than or equal to 80;
wherein M is a doping element.
The lithium metal oxide of the present invention includes at least cobalt, lithium, and sodium. Further, it may be doped with M, and the present invention is not limited to a specific choice of M, and may be a doping element common in the art. For example, at least one of W, mg, ti, mn, al, te, ni, nb, zr, la, F, ce, sr, Y, K, B and P elements.
The present invention does not restrict y, m1 and a too much within the above-defined ranges.
For example, in formula 1, y is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026, 0.028, 0.03, 0.04, or 0.05; m1 is 12, 13, 15, 20, 40, 50, 65, 78 or 80; a is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026, 0.028, 0.030, 0.032, 0.034, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09 or 0.095.
It is emphasized that the above definition of n refers to the molar amount of lithium per unit mole of lithium metal oxide in the positive electrode active material that has not undergone any charge-discharge treatment. The above definition of m1 refers to the ratio of the molar content of Li element to the molar content of Na element per unit mole of lithium metal oxide in the positive electrode active material that has not undergone any charge-discharge treatment, and further, m1 is 22 to 73.
It can be understood that when the positive electrode active material is applied to a lithium ion battery to perform any charge and discharge treatment, the molar amount of lithium per unit mole of lithium metal oxide is different under different charge and discharge mechanisms and charge and discharge nodes, and the ratio of the molar content of Li element to the molar content of Na element per unit mole of lithium metal oxide is also different.
According to the scheme provided by the invention, compared with other positive electrode active materials, after the positive electrode active material comprising the lithium metal oxide is applied to a lithium ion battery, the specific capacity and the cycle performance of the lithium ion battery are obviously improved, and the electric performance of the lithium ion battery is not deteriorated even under the high-voltage working condition. The inventors analyzed based on this phenomenon, and considered that it is possible to: when the molar content ratio of the Li element to the Na element is in a certain range, the lithium metal oxide has a more perfect T2 structure, and part of the sodium element has a supporting function in the structure, so that the lithium metal can promote the lithium ion deintercalation efficiency in Cmca space group of a cubic system, and promote the improvement of the cycle performance and specific capacity of the lithium ion battery.
Further, the inventors found that by classifying doping elements in lithium metal oxides, the performance of the positive electrode active material can be further improved. In some embodiments of the invention, the lithium metal oxide has a formula shown in formula 2;
Li n-y Na y Co 1-a1-a2 M1 a1 M2 a2 O 2 2, 2
In the formula 2, a1 is more than 0 and less than or equal to 0.1, a2 is more than or equal to 0 and less than or equal to 0.1, a1+a2=a;
wherein M1 is selected from at least one of Te, W, al, B, P and K; m2 is a doping element different from M1.
It is understood that the lithium metal oxide of the present invention has a molecular formula shown in formula 2, and specifically, includes at least oxides of cobalt, lithium, sodium, and M1. Further, it may be doped with M2 different from M1, and the present invention is not limited to a specific choice of M2, and may be a doping element common in the art. For example, at least one of Mg, ti, mn, al, te, ni, nb, zr, la, F, ce, sr, Y, K, B and P elements may be used.
The present invention does not restrict y, a1 and a2 excessively within the above-defined ranges.
For example, in formula 2, y is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026, 0.028, 0.03, 0.04, or 0.05; a1 is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026, 0.028, 0.030, 0.032, 0.034, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, or 0.095; a2 is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026, 0.028, 0.030, 0.032, 0.034, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, or 0.095.
In the invention, after the positive electrode active material comprising the lithium metal oxide of the formula 2 is applied to the lithium ion battery, the specific capacity and the cycle performance of the lithium ion battery can be further improved, so that the lithium ion battery can not be deteriorated for a longer time under the high-voltage working condition. The inventors analyzed based on this phenomenon, and considered that it is possible to: on one hand, the doping of M1 is beneficial to supporting the structure of the lithium metal oxide, so that the structural stability of the lithium metal oxide is improved to a certain extent, and therefore, the lithium metal oxide with stable structure is more beneficial to improving the efficiency of lithium ion deintercalation and improving the cycle performance and specific capacity of a lithium ion battery in normal pressure or high pressure working environment; on the other hand, the lithium metal oxide with the crystal characteristics has a more perfect lamellar crystal phase structure, so that the occurrence of mixed discharge phenomenon in the crystal phase can be reduced or inhibited, further, the smooth deintercalation of lithium ions can be realized, and a plurality of small charge-discharge platforms are displayed in the high-voltage charge-discharge process.
In addition to the positive acceleration of the battery's related electrical properties by the lithium metal oxide described above, the performance of the battery is further improved when the coating layer is coated on at least a portion of the surface of the lithium metal oxide. By providing the coating layer, the positive electrode active material has a core-shell structure including a core of lithium metal oxide and a coating layer covering the core. The coating layer helps to reduce or inhibit side reactions of lithium metal oxide and electrolyte, and even when the battery is operated in a high-pressure environment, a stable interface can be formed between the positive electrode active material and the electrolyte, and the cycle performance of the battery is improved by avoiding transition dissolution of metal ions in the positive electrode active ions and avoiding a liquid shortage phenomenon. Meanwhile, the inhibition or reduction of side reaction can also reduce the gas yield in the battery, thereby ensuring the safety performance of the battery.
The invention is not limited to the choice of the material of the coating layer, as long as it can inhibit side reactions and ensure normal migration of lithium ions. In order to further improve the lithium ion conductivity, the coating layer can be made of carbon-containing compounds, fast ion conductors and other materials.
As described above, in the lithium metal oxide which has not undergone any charge-discharge treatment, n is between 0.6 and 0.8, and the molar content ratio m1 of Li element to Na element is between 12 and 80. When the number of charge and discharge cycles is less than 10 after the positive electrode sheet including the positive electrode active material and the lithium metal negative electrode sheet are assembled into a battery and then charged and discharged, n of the lithium metal oxide is between 0.7 and 1.0 and the molar content ratio m2 of the Li element to the Na element is between 16 and 93 when the remaining capacity SOC of the battery is 0 (i.e., in a fully discharged state) and the discharge cut-off voltage is 3.0 to 3.6V. In particular, the composition of the lithium metal oxide is changed after the lithium metal oxide is subjected to charge and discharge application, and particularly the molar quantity of lithium ions is obviously improved. The reason is that the lithium metal oxide having the above crystal structure has a partial vacancy, so that when the lithium metal oxide is applied to charge and discharge, the vacancy can receive lithium atoms from a lithium anode, and the molar quantity of lithium ions is further improved compared with that before the application of charge and discharge. This feature contributes to further improvement in cycle performance and specific capacity of the battery.
Further, when the difference between m2 and m1 is greater than 3, the battery has more excellent specific capacity.
In particular, when the remaining capacity SOC of the battery is 0 (i.e., at the time of full discharge to 3.0V) and the discharge cutoff voltage is 3.0 to 3.6V, n of the lithium metal oxide is between 0.7 and 1.0, the molar content ratio m2 of Li element to Na element is between 26 and 93, and the difference between m2 and m1 is greater than 3, the battery has more excellent cycle performance and specific capacity.
The positive electrode active material can be in a single crystal morphology or a polycrystalline morphology, and the specific morphology is related to the selection and proportion of doping elements. In particular, when polycrystalline in morphology, it is spherical or spheroidal in shape; when in a single crystal morphology, it may be whisker-like, platelet-like, or any other irregular shape.
Further, the median particle diameter of the positive electrode active material of the present invention is 12 to 20 μm, for example, 3 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm. The inventors found that when the median particle diameter of the positive electrode active material satisfies the above requirements, on the one hand, its corresponding specific surface area can satisfy the deintercalation of more lithium ions; on the other hand, the agglomeration phenomenon between the positive electrode active materials is effectively controlled, so that the positive electrode active materials can be stably dispersed in the slurry in the pulping process.
The inventor finds that by further limiting the doping element content and the element type parameters of the lithium metal oxide, a plurality of small discharging platforms in the charging and discharging process show excellent discharging capacity.
It is apparent that the first-stage discharge capacity ratio and the second-stage discharge capacity ratio are excellent in the discharge treatment in the high-pressure environment. Therefore, the positive electrode active material including the lithium metal oxide of the present invention has high pressure resistance, so that the specific capacity of the battery can be increased by subjecting it to a pressure boosting treatment.
The present invention is not limited to the above-described method for preparing a lithium metal oxide, and in one embodiment, the lithium metal oxide of the present invention may be prepared by a method in which a sodium metal oxide represented by formula 1a is mixed with a lithium compound and subjected to ion treatment.
Na x Co 1-a M a O 2 1a
In the formula 1a, x is more than 0.68 and less than 0.74, and a is more than 0 and less than or equal to 0.2.
The ion exchange treatment is a heat treatment process, and specifically refers to a heat treatment of mixing sodium metal oxide and lithium compound and then carrying out heat treatment for not more than 10 hours at 80-300 ℃. After the ion exchange treatment, the system after the ion exchange is washed and dried to finally obtain the lithium metal oxide. Wherein the drying temperature is 80-180 ℃ and the drying time is at least 10h. The apparatus for performing the ion exchange treatment and the drying apparatus are not limited, and for example, the apparatus for performing the ion exchange treatment may be a closed vessel apparatus having a closed function and stirring ability, such as a wet coating reaction apparatus, a coprecipitation reaction apparatus, etc.; the drying apparatus may be a forced air oven, a vacuum drying oven, a rotary kiln, a tray dryer, an oven, or the like.
The above lithium compound may be a lithium source compound commonly used in the art, such as at least one of lithium carbonate, lithium chloride, lithium bromide, lithium iodide, lithium nitrate, lithium hydroxide, lithium fluoride. In the ion exchange treatment, the mass ratio of the lithium compound to the sodium metal oxide is not less than 1:1, preferably (1-3): 1.
further, when it is desired to prepare a positive electrode active material having a coating layer covering the outside of lithium metal oxide, it is necessary to add a coating layer raw material in addition to the raw materials including sodium metal oxide and lithium compound in the ion exchange treatment.
For the sodium metal compound shown in formula 1a, exemplary, it can be prepared by a method comprising the following processes:
at least mixing cobalt source and sodium source according to target proportion, and calcining to obtain sodium metal compound shown in formula 1 a.
Specifically, the calcination treatment is performed at 700 to 900 ℃ for 8 to 50 hours under an oxygen or air atmosphere. The equipment for calcination treatment can be, for example, high-temperature sintering equipment such as muffle furnace, tunnel furnace, roller kiln furnace, tube furnace and the like.
Preferably, the lithium metal oxide of the present invention may also be prepared by a method of mixing a sodium metal oxide represented by formula 1a with a lithium compound and performing an ion treatment.
Na x Co 1-a1-a2 M1 a1 M2 a2 O 2 2a
In the formula 2, a1 is more than 0 and less than or equal to 0.1, a2 is more than or equal to 0 and less than or equal to 0.1, and a1+a2=a.
For example, the sodium metal compound represented by formula 2a may be obtained by mixing the M1 source, the M2 source, the cobalt source, and the sodium source in the target ratio and then performing the calcination treatment.
The mixing of the above sources may be performed by a high-speed mixing apparatus, a sand milling apparatus, a ball milling apparatus, a coulter mixing apparatus, an inclined mixing apparatus, etc., and it should be noted that if a sand milling apparatus, a ball milling apparatus, and a solvent (water, ethanol, or other solvent medium) is added during the ball milling or sand milling, the mixed system needs to be dried after the mixing process is completed. Generally, the mixing time is not more than 4 hours.
The invention is not limited to the specific choice of cobalt source, sodium source, M1 source and M2 source. Illustratively, the cobalt source is selected from one or more of cobalt hydroxide, tricobalt tetraoxide, doped tricobalt tetraoxide, cobaltous oxide, cobalt oxyhydroxide, cobalt nitrate, cobalt sulfate, and the like; the sodium source is selected from one or more of sodium carbonate, sodium nitrate, sodium hydroxide, sodium bicarbonate, sodium sulfate and the like; the M1 source may be an oxide of M1, and when M1 is W, the M1 source is, for example, tungstic acid and/or sodium tungstate, etc.; when M1 is Te, the M1 source is, for example, telluric acid and/or sodium tellurate or the like; when M1 is Al, the M1 source is, for example, one or more of aluminum sulfate, aluminum nitrate, aluminum hydroxide, and the like; when M1 is B, the source of M1 is, for example, boric acid and/or sodium borate, etc.; when M1 is P, the source of M1 is, for example, phosphoric acid and/or sodium phosphate, etc.; when M1 is K, the source of M1 is, for example, one or more of potassium carbonate, potassium nitrate, potassium hydroxide, potassium bicarbonate, potassium sulfate, and the like; examples of the source of M2 may be an oxide of M2, such as one or more of basic magnesium carbonate, magnesium hydroxide, zirconium oxide, yttrium oxide, lanthanum fluoride, nickel oxide, niobium oxide, and the like.
A second aspect of the present invention provides a positive electrode sheet comprising the positive electrode active material according to the first aspect.
Based on the characteristics of the positive electrode active material of the first aspect, the positive electrode sheet of the present invention contributes to improvement of cycle performance and specific capacity of a lithium ion battery.
In one embodiment, the positive electrode sheet of the present invention includes a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector, the positive electrode active layer including the aforementioned positive electrode active material.
It can be understood that the positive electrode active layer includes a conductive agent and a binder in addition to the positive electrode active material. Illustratively, the positive electrode active layer includes 70 to 99wt% of a positive electrode active material, 0.5 to 15wt% of a conductive agent, and 0.5 to 15wt% of a binder, and further includes 80 to 98wt% of a positive electrode active material, 1 to 10wt% of a conductive agent, and 1 to 10wt% of a binder, in terms of mass%.
The choice of the conductive agent and binder is not particularly limited and may be conventional in the art. For example, the conductive agent is at least one selected from conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, single-walled carbon nanotube, multi-arm carbon nanotube, and carbon fiber, and the binder is at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and lithium Polyacrylate (PAALi).
Further, in order to enhance the safety performance, a safety layer may be further provided between the positive electrode active layer and the current collector. The material of the security layer is typically a non-conductive security material, such as iron-containing compounds (e.g., lithium iron phosphate, lithium phosphate, etc.), aluminum-containing compounds (e.g., ceramic alumina), etc. Of course, the security layer also includes a binder, and the ratio of binder to security material may be further determined according to specific needs.
In some embodiments of the invention, the positive electrode active layer has a compacted density of 3.5g/cm or more 3 In this case, the cycle performance and specific capacity of the battery can be further improved.
The third aspect of the present invention also provides a lithium ion battery comprising the positive electrode sheet described above, and thus exhibiting outstanding cycle performance and specific capacity.
According to the invention, the lithium ion battery further comprises a negative plate, a diaphragm and an electrolyte.
Illustratively, the electrolyte is a conventional electrolyte known in the art including a lithium salt and a solvent containing ethylene carbonate (abbreviated EC), diethyl carbonate (abbreviated DEC), propylene carbonate (abbreviated PC), fluoroethylene carbonate (abbreviated FEC). Further, the electrolyte further comprises an additive shown in the formula T, wherein the mass percentage of the additive in the electrolyte is 0.1-10 percent.
The negative electrode sheet may be, for example, a lithium metal-rich negative electrode sheet, which may be, for example, a lithium foil or a negative electrode sheet as shown in fig. 1. Specifically, the anode sheet in fig. 1 includes an anode current collector 101, an anode active layer 20, and a lithium material layer 30, which are stacked. The negative electrode sheet in fig. 1 is provided on both sides, but it is needless to say that the negative electrode active layer 20 and the lithium material layer 30 may be provided on only one side of the negative electrode current collector. The lithium material layer is, for example, a lithium foil, and further, the surface density of the metal lithium in the lithium material layer is 0.09mg/cm 2-3.5 mg/cm2; the anode active layer includes an anode active material, a conductive agent, and a binder.
In one embodiment, the negative electrode active layer comprises, by mass, 70-99% of a negative electrode active material, 0.5-15% of a conductive agent, and 0.5-15% of a binder, and further comprises 80-98% of a negative electrode active material, 1-10% of a conductive agent, and 1-10% of a binder. Wherein the negative electrode active material is selected from one or more of artificial graphite, natural graphite, hard carbon, mesophase carbon microsphere, lithium titanate, silicon carbon and silicon oxide.
The membrane is illustratively a polypropylene-based material, or a rubberized membrane coated with ceramic on one or both sides on the basis thereof.
The lithium ion battery is suitable for a high-voltage system, and particularly, under the condition that the lithium ion button battery comprising the positive plate is more than or equal to 4.55V (relative to lithium), the gram capacity of the positive plate is more than or equal to 225mAh/g, and the positive plate has excellent cycle performance at the same time of more than or equal to 4.50V (corresponding to the negative plate).
Therefore, the lithium ion battery with good cycling stability and high gram capacity at higher voltage of 4.50V and the like can meet the use requirement of light and thin high-end digital products.
The technical scheme of the invention will be further explained below with reference to specific examples.
Example 1
The positive electrode active material of this example was prepared as follows:
(1) Weighing 36.56g of sodium carbonate powder and 291.05g of cobalt nitrate hexahydrate powder, putting the sodium carbonate powder and the cobalt nitrate hexahydrate powder into high-speed mixing equipment, setting a mixing program, mixing at 300rpm for 3 minutes, mixing at 500rpm for 5 minutes, mixing at 1000rpm for 10 minutes, taking out the mixture, and considering that the mixture is uniform after confirming that no white sodium carbonate small white spots exist in the mixture;
(2) Taking about 30g of uniformly mixed mixture, uniformly filling the mixture into a ceramic crucible, performing high-temperature sintering by using a well-type muffle furnace with equipment model of VBF-1200X, performing constant-temperature sintering for 10 hours when the temperature of the mixture is raised to 750 ℃ at a temperature of 5 ℃/min, taking out a sample after naturally cooling to normal temperature after sintering, and detecting by an inductively coupled plasma spectroscope (ICP) to obtain sodium metal oxide Na 0.69 CoO 2 ；
(3) Firstly weighing 10.49g of lithium hydroxide monohydrate and 17.24g of lithium nitrate particles in a reaction vessel, respectively adding two lithium compounds into the reaction vessel, and weighing 10g of Na synthesized in the step (2) 0.69 CoO 2 Pouring the mixture into a reaction vessel, and performing primary mixing and ion exchange at 280 ℃ for 0.5h to obtain a crude product;
(4) And (3) carrying out suction filtration and washing on the crude product by using deionized water for 3 times, and drying at 90 ℃ for 8 hours to obtain a sample No. 1A.
The detection analysis was performed on # 1 using ICP, and the specific results are shown in Table 1.
Example 2
The preparation method of the positive electrode active material of this example is basically the same as that of example 1, except that:
in the step (3), ion exchange is carried out for 1.2 hours at 260 ℃ to obtain a crude product; after the treatment of the step (4), a sample 2A#Li is obtained 0.70 Na 0.025 CoO 2 。
Example 3
The preparation method of the positive electrode active material of this example is basically the same as that of example 1, except that:
in the step (3), ion exchange is carried out for 3.4 hours at the temperature of 95 ℃ to obtain a crude product; after the treatment of the step (4), a sample 3A#Li is obtained 0.72 Na 0.023 CoO 2 。
Example 4
The preparation method of the positive electrode active material of this example is basically the same as that of example 1, except that:
in the step (3), ion exchange is carried out for 3.0h at 105 ℃ to obtain a crude product; after the treatment of the step (4), a sample 4A#Li is obtained 0.73 Na 0.017 CoO 2 。
Example 5
The preparation method of the positive electrode active material of this example is basically the same as that of example 1, except that:
the step (1) is as follows: putting 36.56g of sodium carbonate powder, 0.21g of potassium carbonate powder, 282.31g of cobalt nitrate hexahydrate powder and 1.21g of nano magnesium oxide powder into high-speed mixing equipment, setting a mixing program, mixing at 300rpm for 3 minutes, mixing at 500rpm for 5 minutes, mixing at 1000rpm for 10 minutes, taking out the mixture, and recognizing that white sodium carbonate small white spots exist in the mixture and mixing uniformly;
the sodium metal oxide obtained in the step (2) is Na 0.69 K 0.003 Co 0.97 Mg 0.03 O 2 ；
After the treatment of the step (4), a sample 5A#Li is obtained 0.71 Na 0.02 K 0.003 Co 0.97 Mg 0.03 O 2 。
Example 6
The preparation method of the positive electrode active material of this example is basically the same as that of example 5, except that:
in the step (3), ion exchange is carried out for 2.8 hours at the temperature of 100 ℃ to obtain a crude product; after the treatment of the step (4), a sample 6A#Li is obtained 0.72 Na 0.021 K 0.003 Co 0.97 Mg 0.03 O 2 。
Example 7
The preparation method of the positive electrode active material of this example is basically the same as that of example 5, except that:
in the step (3), ion exchange is carried out for 1.5 hours at 260 ℃ to obtain a crude product; after the treatment of the step (4), a sample 7A#Li is obtained 0.73 Na 0.017 K 0.003 Co 0.97 Mg 0.03 O 2 。
Comparative example 1
The positive electrode active material of this comparative example was prepared in substantially the same manner as in example 1, except that:
in the step (3), ion exchange is carried out for 24 hours at the temperature of 75 ℃ to obtain a crude product; after the treatment of the step (4), a sample 1a#Li is obtained 0.50 Na 0.48 CoO 2 。
Comparative example 2
The positive electrode active material of this comparative example was prepared in substantially the same manner as in example 1, except that:
in the step (3), ion exchange is carried out for 24 hours at 90 ℃ to obtain a crude product; after the treatment of the step (4), a sample 2a#Li is obtained 0.89 Na 0.005 CoO 2 。
Comparative example 3
The positive electrode active material of this comparative example was prepared in substantially the same manner as in example 5, except that:
in the step (3), ion exchange is carried out for 0.1h at 280 ℃ to obtain a crude product; after the treatment of the step (4), a sample 3a#Li is obtained 0.3 9 Na 0.60 K 0.003 Co 0.97 Mg 0.03 O 2 。
Comparative example 4
The positive electrode active material of this comparative example was prepared in substantially the same manner as in example 5, except that:
in the step (3), ion exchange is carried out for 30 hours at the temperature of 85 ℃ to obtain a crude product; after the treatment of the step (4), a sample 4a#Li is obtained 0.86 Na 0.006 K 0.003 Co 0.97 Mg 0.03 O 2 。
Comparative example 5
The positive electrode active material of this comparative example was prepared in substantially the same manner as in example 5, except that:
in the step (3), the mixture is separated at 280 DEG CSub-exchanging for 0.35h to obtain a crude product; after the treatment of the step (4), a sample 5a#Li is obtained 0.69 Na 0.06 K 0.003 Co 0.97 Mg 0.03 O 2 。
Comparative example 6
The positive electrode active material of this comparative example was prepared in substantially the same manner as in example 1, except that:
in the step (3), ion exchange is carried out for 15 hours at 280 ℃ to obtain a crude product; after the treatment of the step (4), a sample 6a#Li is obtained 0.93 Na 0.03 CoO 2 。
Test example 1
1) The morphology of the positive electrode active materials of example 1 and comparative example 1 was tested using SEM, respectively, and as shown in fig. 2 and 3, the positive electrode active material of example 1 had a large dispersion of particle diameters, and lithium ions were able to be more sufficiently extracted, contributing to improvement of specific capacity and cycle performance of the battery.
2) XRD diffractions were performed on all the products of examples and comparative examples, and the results are shown in table 2.
Fig. 4 is an XRD pattern of the positive electrode active material in example 1 of the present invention. As can be seen from fig. 4, the positive electrode active material in example 1 of the present invention has one characteristic peak at 18.06 ° and one characteristic peak at 67.43562 °.
Test example 2
After the products of all examples and comparative examples were fabricated as positive electrode sheets, they were assembled with a negative electrode sheet, an electrolyte and a separator in the following manner to obtain lithium ion batteries. The method comprises the following steps:
1) The positive electrode active materials in examples and comparative examples were mixed with conductive carbon black and PVDF in a weight ratio of 96% to 2% respectively, and dispersed to obtain positive electrode slurry. Coating the slurry on an aluminum foil current collector, and rolling to prepare a positive plate;
2) Artificial graphite, styrene diene rubber (SBR), sodium carboxymethylcellulose and conductive carbon black are mixed according to the weight ratio of 94% to 3% to 2% to 1%, and the mixture is dispersed in water, and then mixed by double planetary so as to obtain the cathode slurry. Coating the slurry on a copper current collector, and then rolling and drying;
then a lithium material layer is overlapped on the surface of the anode active layer in a rolling mode, wherein the lithium material layer is a lithium foil, and the area density of metal lithium is 1.0mg/cm 2 Finally, the negative plate containing lithium metal is obtained.
3) And then assembling the positive plate, the negative plate and the diaphragm into a lithium ion battery, and injecting a non-aqueous electrolyte.
Wherein the electrolyte is a conventional electrolyte known in the art, and is represented by ethylene carbonate (abbreviated as EC): diethyl carbonate (abbreviated as DEC): propylene carbonate (abbreviated PC) =2: 5:3, adding fluoroethylene carbonate (abbreviated as FEC) accounting for 5 percent of the total mass of the electrolyte, and adding lithium hexafluorophosphate (abbreviated as LiPF) accounting for 13 percent of the total mass of the electrolyte 6 ) And the additive is shown in the formula T, wherein the content of the additive accounts for 2% of the total content of the electrolyte. The capacity retention rate of each lithium ion battery is tested, and the specific test method comprises the following steps: the discharge capacity at the first cycle and the discharge capacity at 500 th cycle were measured at 25℃by constant-current charging to 4.50V at a charge rate of 1C, constant-voltage charging to 4.50V at a charge rate of 0.05C, and discharging to 3.0V at a discharge rate of 1C, and repeating 500 times of this charge-discharge cycles, and the capacity retention after 500 cycles was obtained according to the following formula, and the results are shown in Table 2.
Capacity retention rate q= (discharge capacity at 500 th cycle)/(discharge capacity at first cycle) ×100%
Test example 3
After the products of all examples and comparative examples were fabricated as positive electrode sheets, they were assembled with a negative electrode sheet, an electrolyte and a separator in the following manner to obtain a button cell. The method comprises the following steps:
the positive electrode active materials in examples and comparative examples were mixed with conductive carbon black (SP) and PVDF, respectively, in a weight ratio of 80% to 10%, and dispersed to obtain positive electrode pastes. Coating the slurry on an aluminum foil current collector, rolling to prepare a positive plate, then drying and weighing the positive plate by using a film with a small wafer with the punching diameter of 12mm, and then assembling the positive plate into a button cell by using a 2025 button cell shell and a Li metal wafer as a negative electrode in a glove box under an Ar protective atmosphere together with conventional high-voltage lithium cobaltate electrolyte.
And (3) after standing the obtained button cells for 4 hours in a conventional environment, testing the first charge and discharge capacity, wherein the testing conditions are as follows: after 0.1C was charged to 4.55V and constant voltage charged to 0.025C was turned off, the mixture was allowed to stand for 3 minutes, and then 0.1C was discharged to 3.0V. In the discharging process, the first discharging full electric quantity C0 and the first charging capacity are recorded respectively, and the first efficiency is calculated. The results are shown in Table 2.
Test example 4:
the lithium ion battery in test example 2 was discharged to 3.0V at a current of 1/10 of the rated capacity, the voltage was found to be 3.0 to 3.6V by testing, then the lithium ion battery was disassembled, the positive electrode sheet was taken out, immersed in dimethyl carbonate (DMC) for 3 hours, dried in the air, baked in a muffle furnace at 300 ℃ for 3 hours, and then sample powder was obtained after sieving with a 200-mesh sieve, and the content of each element in the sample powder was tested by ICP, and the test results are shown in table 2.
TABLE 1
TABLE 2
From tables 1 and 2, it can be seen that:
1. according to the examples and comparative examples, different preparation parameters such as reaction temperature, reaction time, raw material selection difference, etc., have a certain influence on the composition and crystal structure of the lithium metal oxide, and ultimately affect the relevant performance of the lithium ion battery. In particular, it is necessary to strictly control the synthesis conditions so as to obtain a pure-phase positive electrode active material.
2. As can be seen from table 2, the positive electrode active material prepared in the embodiment of the present invention has more excellent gram capacity and cycle performance when applied to a lithium ion battery.
3. As can be seen from examples 1 to 4 and examples 5 to 7, the cathode active material having the doping element is substantially unchanged in gram capacity and significantly enhanced in cycle performance when applied to a lithium ion battery, as compared with the cathode active material having no doping element.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.
Claims (10)
1. A positive electrode active material, characterized in that the positive electrode active material comprises a lithium metal oxide having a molecular formula shown in formula 1;
in an X-ray diffraction pattern, the lithium metal oxide is a Cmca space group of a cubic crystal system and has 002 peaks with 2 theta of 17.9-18.1 degrees and 131 peaks with 2 theta of 67.0-67.5 degrees;
Li n-y Na y Co 1-a M a O 2 1 (1)
In the formula 1, n is more than or equal to 0.6 and less than or equal to 0.8, y is more than or equal to 0 and less than or equal to 0.05, and a is more than or equal to 0 and less than or equal to 0.2;
the molar content ratio m1 of the Li element to the Na element satisfies: m1 is more than or equal to 12 and less than or equal to 80;
wherein M is a doping element.
2. The positive electrode active material according to claim 1, wherein the lithium metal oxide has a molecular formula represented by formula 2;
Li n-y Na y Co 1-a1-a2 M1 a1 M2 a2 O 2 2, 2
In the formula 2, a1 is more than 0 and less than or equal to 0.1, a2 is more than or equal to 0 and less than or equal to 0.1, a1+a2=a;
wherein M1 is selected from at least one of Te, W, al, B, P and K; m2 is a doping element different from M1.
3. The positive electrode active material according to claim 1 or 2, characterized in that the positive electrode active material is composed of a base particle including the lithium metal oxide and a coating layer covering at least a part of the surface of the base particle.
4. The positive electrode active material according to claim 1 or 2, wherein when the cutoff voltage is 3.0 to 3.6V and the SOC is zero, 0.7.ltoreq.n.ltoreq.1.0, and the molar content ratio m2 of Li element to Na element satisfies: m2 is more than or equal to 16 and less than or equal to 93.
5. The positive electrode active material according to claim 4, wherein m2-m1 > 3.
6. The positive electrode active material according to claim 1 or 2, wherein the positive electrode active material has a median particle diameter of 12 μm to 20 μm.
7. A positive electrode sheet, characterized in that the positive electrode sheet comprises the positive electrode active material according to any one of claims 1 to 6.
8. The positive electrode sheet according to claim 7, wherein the positive electrode sheet includes a current collector, a safety layer, and a positive electrode active layer;
the safety layer is clamped between the current collector and the positive electrode active layer, and the positive electrode active layer comprises the positive electrode active material.
9. The positive electrode sheet according to claim 8, wherein the positive electrode active layer has a compacted density of 3.5g/cm or more 3 。
10. A lithium ion battery comprising the positive electrode sheet according to any one of claims 7 to 9.
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